Standard Transmissions

Standard Transmissions
Chapter 15 Standard Transmissions

Objectives (1 of 3) Identify the types of gears used in truck transmissions. Interpret the language used to describe gear trains and calculate gear pitch and gear ratios. Explain the relationship between speed and torque from input to output in different gear arrangements.

Objectives (2 of 3) Identify the major components in a typical transmission including input and output shafts, mainshaft and countershaft gears, and shift mechanisms. Describe the shift mechanisms used in heavy-duty truck transmissions.

Objectives (3 of 3) Outline the role of main and auxiliary (compound) gear sections in a typical transmission, and trace the powerflow from input to output in different ratios. Describe the operating principles of range shift and splitter shift air systems. Define the roles of transfer cases and PTOs in heavy-duty truck operation.

Gears A gear can be used in any of the following roles:
The shaft can drive the gear. The gear can drive the shaft. The gear can be left free to turn on the shaft (it idles). Sets of gears can be arranged to do the following: Multiply torque and decrease speed Increase speed and decrease torque Transfer torque and speed unchanged GEARS Gears are used in a transmission to transmit rotational motion or torque. They are usually mounted on shafts. Gears positioned on parallel shafts with their teeth in mesh transmit rotating motion from one shaft to another. A gear can be used in any of the following roles: The shaft can drive the gear. The gear can drive the shaft. The gear can be left free to turn on the shaft (it idles). Sets of gears can be arranged to do the following: Multiply torque and decrease speed Increase speed and decrease torque Transfer torque and speed unchanged Any study of transmissions requires some knowledge of gear terminology. Here are some of the common gear terms you should be familiar with: Drive Gear (Input). A drive gear or driving gear is one that drives another gear or causes another gear to turn. Driven Gear (Output). A driven gear is one that is driven by a drive gear or a shaft. Rotation and Direction of Rotation. Rotation is the term we use to describe anything that turns

Gear Design (1 of 2) GEAR DESIGN
You should be familiar with the some basic gear geometry because it is required when performing gear train adjustments and failure analysis. Figure 15–2 shows some of the terms used to describe gear tooth geometry; you should reference this in the following explanations. Gear pitch refers to the number of teeth per given unit of pitch diameter. You can determine gear pitch by dividing the total number of teeth in a gear by the gear’s pitch diameter. Pitch diameter is the root-to-root diameter between teeth across the face of a gear. For example, if a gear has 36 teeth and a 6-inch pitch diameter, it has a gear pitch of 6 (Figure 15–3). Gears must have the same pitch in order to operate together. A 5-pitch gear will mesh only with another 5-pitch gear, a 6-pitch only with a 6-pitch, and so on. The teeth of a pair of mating gears, while in mesh, pass through the stages of contact (Figure 15–4) that we can describe as coming into mesh, full mesh, and coming out of mesh. Coming into mesh occurs at the initial contact of the dedendum (lower tooth section closer to the root) on the driving gear with the addendum (upper tooth section closer to the apex) of the driven gear. At this point of torque transfer, tooth loading (LT) is relatively light since most tooth loading is sustained by gear teeth that are in full mesh. As the gears rotate, contact between intermeshing teeth progresses in a sliding action. Sliding velocity decreases until it zeros when the contact points reach the intersection of their common pitch lines. At full mesh, when the two teeth meet at their common or operating pitch line, there is only a rolling motion, no sliding action. However, at this stage, tooth loading is at its greatest. Coming out of mesh, the two mating teeth again move in a sliding action, essentially the opposite of the initial contact stage. Each gear tooth profile has a theoretical perfect shape. Each manufacturer determines acceptable tolerances for the gears they use in their assemblies, as shown in Figure 15–5. Actual tooth profile can fall anywhere within the tolerance window. A gear tooth must be parallel with the centerline of its shaft—again within a specified tolerance window. This tolerance window is illustrated in Figure 15–6. This tolerance window makes it possible to mate gears with minor variations without causing operational failures. Some manufactured transmission mainshaft gearing is crowned, as shown in Figure 15–7. Crowning is a slight curvature machined from end to end on a mainshaft gear tooth. Crowning prevents highly concentrated contact loads that could result in tooth surface damage.

Gear Design (2 of 2) You should be familiar with the some basic gear geometry because it is required when performing gear train adjustments and failure analysis. Figure 15–2 shows some of the terms used to describe gear tooth geometry; you should reference this in the following explanations. Gear pitch refers to the number of teeth per given unit of pitch diameter. You can determine gear pitch by dividing the total number of teeth in a gear by the gear’s pitch diameter. Pitch diameter is the root-to-root diameter between teeth across the face of a gear. For example, if a gear has 36 teeth and a 6-inch pitch diameter, it has a gear pitch of 6 (Figure 15–3). Gears must have the same pitch in order to operate together. A 5-pitch gear will mesh only with another 5-pitch gear, a 6-pitch only with a 6-pitch, and so on. The teeth of a pair of mating gears, while in mesh, pass through the stages of contact (Figure 15–4) that we can describe as coming into mesh, full mesh, and coming out of mesh. Coming into mesh occurs at the initial contact of the dedendum (lower tooth section closer to the root) on the driving gear with the addendum (upper tooth section closer to the apex) of the driven gear. At this point of torque transfer, tooth loading (LT) is relatively light since most tooth loading is sustained by gear teeth that are in full mesh. As the gears rotate, contact between intermeshing teeth progresses in a sliding action. Sliding velocity decreases until it zeros when the contact points reach the intersection of their common pitch lines. At full mesh, when the two teeth meet at their common or operating pitch line, there is only a rolling motion, no sliding action. However, at this stage, tooth loading is at its greatest. Coming out of mesh, the two mating teeth again move in a sliding action, essentially the opposite of the initial contact stage. Each gear tooth profile has a theoretical perfect shape. Each manufacturer determines acceptable tolerances for the gears they use in their assemblies, as shown in Figure 15–5. Actual tooth profile can fall anywhere within the tolerance window. A gear tooth must be parallel with the centerline of its shaft—again within a specified tolerance window. This tolerance window is illustrated in Figure 15–6. This tolerance window makes it possible to mate gears with minor variations without causing operational failures. Some manufactured transmission mainshaft gearing is crowned, as shown in Figure 15–7. Crowning is a slight curvature machined from end to end on a mainshaft gear tooth. Crowning prevents highly concentrated contact loads that could result in tooth surface damage.

Gear Ratios GEAR RATIOS
As we stated earlier in this chapter, only gears with matching pitch can be meshed. When in mesh, the relative speed of the meshed gears depends on the ratio of the number of teeth on the driving (input) gear to the number of teeth on the driven (output) gear. In Figure 15–8, the two gears shown in A are the same size and have the same number of teeth. Because both gears are the same size, the speed of both gears has to be equal so that a direct drive, reverse ratio results. If the objective was to produce direct drive but maintain the same direction of rotation, a third gear of the same size and number of teeth would be required. In Figure 15–8B, a small drive (input) gear turns a larger driven (output) gear. Because the driving gear has fewer teeth than the gear it is driving, the speed of the driven (output) gear must be slower than that of the input gear. This drive arrangement produces a reduction ratio, because the output speed is reduced. When the driving gear has more teeth than the driven gear (as shown in Figure 15–8C), the output speed of the driven gear increases. Whenever output speed exceeds input speed, it is commonly referred to as overdrive. The relative speed of two meshed gears can always be calculated by comparing the size and speed of each. Multiply the number of teeth of one gear by the speed of that gear, and divide that number by the number of teeth on the other gear. For example, if we wanted to calculate the speed of a driven gear with 75 teeth when the driving gear has 45 teeth and is rotating at 200 rpm we would use the following formula: Building the known data into this equation gives us: (note that the values on top of each line are divided by those below the line) n this way, an input speed of 200 rpm is reduced to an output speed of 120 rpm. The relationship between input and output speeds is expressed as gear ratio. Gear ratio can be calculated in a number of ways depending on the known data. One method is to divide the speed of the driving (input) gear by the speed of the driven (output) gear or shaft. So using the above example we have: Gear ratio can also be calculated by dividing the number of teeth on the driven gear by the number of teeth on the driving gear. Again, using our above data, the equation would be: n both cases, we produced the same result, telling us that to produce one full rotation of the driven or output gear we have to turn the driving or input gear 1.66 times.

Speed Versus Torque SPEED VERSUS TORQUE
Torque is rotational force or effort. Anything that rotates requires torque to make it turn. Torque is calculated by multiplying the applied force by its distance from the centerline of rotation. An example of this simple law of physics is demonstrated whenever a torque wrench is used. Figure 15–9 shows us that when a force of 10 pounds is applied perpendicular to the centerline of a bolt at a distance 1 foot from the centerline, 10 pound-feet of torque is generated at the centerline of rotation. The torque wrench acts as a lever to apply this force. Meshed gears use this same leverage principle to transfer torque. If two gears in mesh have the same number of teeth, they will rotate at the same speed, and the input gear will transfer an equal amount of torque to the output gear (Figure 15–10A). We have already determined that when a driven gear is larger than its driving gear, output speed decreases. But how is torque affected? Figure 15–10B illustrates a small gear with 12 teeth driving a large gear with 24 teeth. This results in a gear ratio of 2:1, with the output speed being half of the input speed. In this example, torque at the input shaft of the driving gear is 10 pound-feet. The distance from the centerline of this input shaft to the gear teeth is 1 foot. This means the driving gear transfers 10 pounds of force to the teeth of the larger driven gear. The distance between the teeth of the driven gear and the centerline of its output shaft is 2 feet. This means that torque at the output shaft is: 10 pounds (force) x 2 feet (distance) = 20 lb.-ft In this instance, torque has doubled. The torque increase from a driving gear to a driven gear is directly proportional to the speed decrease. When speed is halved, torque doubles. If we go back and take a look at the results of the first equation, we calculated a gear ratio of 1.66:1, meaning that the output gear rotates 1.66 times slower than the input gear. But in reducing the output speed, output torque has increased by a ratio of 1.66 times. So if we say that torque at the input gear input is 100 pound-feet, then the gear reduction increases output torque by 1.66 times: Output torque = 1.66 x 100 pound-feet = 166 lb.-ft Most of the gearing in standard transmission gearing is speed reducing/torque increasing. In some transmissions, the top gear produces a 1:1 ratio where speed and torque are transferred directly from the input to the output shaft. In this case, engine flywheel and transmission output shaft rpms would be equal. In some transmissions, the top gear or gears are overdrive gear combinations, resulting in a speed increasing/ torque-reducing relationship between input and output. We express overdrive gear ratios using a decimal point, so if a gear ratio were said to be 0.85:1, to rotate the output shaft through one revolution the input shaft would only have to turn 0.85 times. Output speed would therefore be times greater (1.00 divided by 0.85) than input speed. However, if you recall what we said about the relationship between speed and torque, we know that output torque is reduced to 0.85 of input torque. So if input speed is 100 rpm and input torque is 100 pound-feet, the output values can be calculated to be rpm and 85 pound-feet torque.

Idler Gears An idler gear may be used to transfer torque without changing the direction of rotation. Idler gears are also used to provide reverse gearing. If two idler gears are used, the driven gear will rotate in the opposite direction of the drive gear. Idler gears can also transfer power in place of a chain drive or belt drive. Idler gears do not affect the relative speeds of either the drive or driven gears. IDLER GEARS An idler gear is often placed between a drive gear and a driven gear to act as an intermediary to transfer torque without changing the rotational direction or gear ratio of the gear set. (Figure 15–11). This allows the driven gear to rotate in the same direction as the drive gear. Idler gears are used in reverse gearing. If two idler gears are used, the driven gear will rotate in the direction opposite to that of the drive gear. Idler gears can also serve as a transfer medium between the drive and driven gears in place of a chain drive or belt drive. Idler gears are designed to not affect the relative speeds of either the drive or driven gears.

Spur Gears Teeth are cut straight, parallel to the shaft.
Only one tooth is in full contact at any given moment. Spur gear teeth minimize the possibility of popping out of gear. For this reason, spur gears are often used in the reverse gear train. A disadvantage of spur gears is noise. At higher turning speeds, their clicking noise becomes a constant whine. Figure 15–12 here TYPES OF GEARS Different types of gears are used in transmission assemblies. The following types are commonly used. Spur Gears The spur gear is the simplest gear design used in manual transmissions. As shown in Figure 15–12, spur gear teeth are cut straight, parallel to the gear shaft. During operation, enmeshed spur gears have only one tooth in full contact at any given moment. The straight-tooth design is an advantage of a spur gear. Straight teeth minimize the possibility of popping out of gear, a critical consideration during acceleration, deceleration, and reverse operation. For this reason, spur gears are often used in the reverse gear train. A disadvantage of spur gears is noise, specifically a clicking noise that occurs as teeth come into contact with each other. At higher turning speeds, the clicking noise becomes a constant whine. Helical gears are quieter and, because of this, are often used in preference to spur gears to eliminate gear whine.

Helical Gears Teeth are cut at an angle. (helical to the axis of rotation) Two or more teeth may be in mesh at the same time providing more evenly distributed load. They are useful in applications requiring high torque to transfer loads. They perform more quietly than spur gears because they mesh with mating gears with a wiping action. The main disadvantage of helical gears is the longitudinal thrust they create during operation. Shop Talk When a small gear is meshed with a larger gear, as shown in Figure 15–12, the smaller gear is often called a pinion or pinion gear, regardless of its tooth design. A helical gear has teeth that are cut at an angle—that is, they are helical to the gear axis of rotation (Figure 15–13). This allows two or more teeth to be in mesh at the same time. Helical gears permit the tooth load to be evenly distributed and are used in applications requiring high torque transfer loads. In addition, helical gears perform more quietly than spur gears because they create a wiping action as they come into and out of mesh with mating gears. The main disadvantage of helical gears is the longitudinal thrust they create in operation. As torque transfers from one gear to its mating gear, fore or aft thrust is created on each shaft. This fore or aft force is known as axial thrust force; it has to be absorbed by thrust washers, other transmission gears, shafts, and, ultimately, the transmission housing. Helical gears can have either right- or left-handed geometry, depending on the direction of the spiral when viewed face-on. When designed to mesh, helical gears must be mounted on parallel shafts, with one gear using right-handed geometry and its mate using left-handed geometry. Two helical gears manufactured with helices in the same-direction spiral cannot mesh in a parallel-mounted arrangement. Both helical and spur gears are commonly used in heavy-duty truck transmission gearing.

Gear Train Configurations
Twin-countershaft transmissions deliver torque equally to two countershafts with each gear set carrying only half of the load. Torque path travels through the countershaft(s) until it reaches the selected gearing. This gearing routes the torque path back to the mainshaft and from there to any auxiliary gearing present. GEAR TRAIN CONFIGURATIONS A truck standard transmission usually consists of a mainshaft and one, two, or three countershafts. These shafts are mounted parallel to one another. Torque from the engine is transmitted from a transmission input shaft at the front of the transmission through gearing to the countershaft(s). This torque path travels through the countershaft(s) until it reaches the selected gearing. This gearing routes the torque path into the transmission mainshaft and from there out to a compound (auxiliary gearing) and the driveline components. Single- ountershaft transmissions are used in a few heavy-duty applications but are more common in medium-duty trucks. Most heavy-duty trucks use a double- or twin-countershaft design (Figure 15–14). In a twin-countershaft transmission, torque delivered to the transmission input shaft is divided equally between two shafts. This means that each countershaft gear set carries only half the load of a similar gear set used on a single-countershaft design.

Sliding Gear Shift Gears on the mainshaft are moved until they mesh with the desired gear on the countershaft. Spur-cut sliding gears are needed. Shifting is unsynchronized; grinding and gear clash are a problem. Sliding gears are prone to gear chipping and fracture. Currently, the only gear ratios using sliding gears are first and reverse. SLIDING GEAR SHIFT A transmission that uses a sliding gearshift mechanism has a mainshaft and a countershaft supported parallel to each other. To change from one speed/torque range to another, gears on the mainshaft are moved longitudinally until they engage the desired gear on the countershaft. To effect this movement, spur-cut sliding gears are used: these have a shift collar integral with the gear. When the driver makes a shift, a shift fork or yoke engages with a collar on the gear and slides it on the mainshaft until it is brought into mesh with a mating gear on the countershaft. Some older heavy-duty truck transmissions used this type of sliding gear shift arrangement for all speed ranges. However, this type of shifting is unsynchronized, and it was a problem for drivers to precisely match the speed of meshing gears. As a result, grinding and gear clash were a problem especially with inexperienced drivers. Sliding gear shift mechanisms resulted in transmissions prone to rapid wear, gear teeth chipping, and fracture. In modern standard truck transmissions, the only gear ratios that generally use spur-type sliding gears are first and reverse. The other gears in the transmission use some form of sliding clutch collar or synchronizer to engage each gear range. In addition, all non-sliding gears are in constant mesh with their mating countershaft gears. Figure 15–16 illustrates a five speed single-countershaft truck transmission that uses a combination of sliding gear and collar shift mechanisms to change ratios.

First Gear (1 of 3) When the shift fork or yoke is moved by the gearshift lever in the cab, it slides the collar and gear either to the front or rear of the transmission housing. Sliding it forward (to the left) engages the first and reverse sliding gear on the mainshaft with the first gear on the countershaft. First Gear Using the callout numbers in Figure 15–16, we will walk you through how shifts are made in this simple transmission. You should be able to identify callout 18 as the first and reverse sliding gear and callout 17 is its integral shift collar. When the shift fork or yoke (this is not shown, but it engages with the shift collar 17) is moved by the gearshift lever in the cab, it slides the collar and gear either to the front or rear of the transmission housing. Sliding it forward (to the left) engages the first and reverse sliding gear on the mainshaft with the first gear (callout 15) on the countershaft. This results in directing powerflow through the first gear as shown in Figure 15–17. The torque path is as follows: It flows from the engine flywheel through the clutch plate splines to the transmission input shaft, then (2) through the input shaft gear (5) to the countershaft-driven gear (6). Powerflow is then transmitted through the countershaft to the first gear (15) and up to the first and reverse sliding gear (18) on the mainshaft (16). Because the first and reverse sliding gear is splined to the mainshaft, powerflow is directed through the mainshaft and out to the vehicle driveline.

First Gear (2 of 3) This results in directing powerflow through the first gear as shown. The torque path is as follows: It flows from the engine flywheel through the clutch plate splines to the transmission input shaft, then (2) through the input shaft gear (5) to the countershaft-driven gear (6). First Gear Using the callout numbers in Figure 15–16, we will walk you through how shifts are made in this simple transmission. You should be able to identify callout 18 as the first and reverse sliding gear and callout 17 is its integral shift collar. When the shift fork or yoke (this is not shown, but it engages with the shift collar 17) is moved by the gearshift lever in the cab, it slides the collar and gear either to the front or rear of the transmission housing. Sliding it forward (to the left) engages the first and reverse sliding gear on the mainshaft with the first gear (callout 15) on the countershaft. This results in directing powerflow through the first gear as shown in Figure 15–17. The torque path is as follows: It flows from the engine flywheel through the clutch plate splines to the transmission input shaft, then (2) through the input shaft gear (5) to the countershaft-driven gear (6). Powerflow is then transmitted through the countershaft to the first gear (15) and up to the first and reverse sliding gear (18) on the mainshaft (16). Because the first and reverse sliding gear is splined to the mainshaft, powerflow is directed through the mainshaft and out to the vehicle driveline.

First Gear (3 of 3) Powerflow is then transmitted through the countershaft to the first gear (15) and up to the first and reverse sliding gear (18) on the mainshaft (16). Because the first and reverse sliding gear is splined to the mainshaft, powerflow is directed through the mainshaft and out to the vehicle driveline. First Gear Using the callout numbers in Figure 15–16, we will walk you through how shifts are made in this simple transmission. You should be able to identify callout 18 as the first and reverse sliding gear and callout 17 is its integral shift collar. When the shift fork or yoke (this is not shown, but it engages with the shift collar 17) is moved by the gearshift lever in the cab, it slides the collar and gear either to the front or rear of the transmission housing. Sliding it forward (to the left) engages the first and reverse sliding gear on the mainshaft with the first gear (callout 15) on the countershaft. This results in directing powerflow through the first gear as shown in Figure 15–17. The torque path is as follows: It flows from the engine flywheel through the clutch plate splines to the transmission input shaft, then (2) through the input shaft gear (5) to the countershaft-driven gear (6). Powerflow is then transmitted through the countershaft to the first gear (15) and up to the first and reverse sliding gear (18) on the mainshaft (16). Because the first and reverse sliding gear is splined to the mainshaft, powerflow is directed through the mainshaft and out to the vehicle driveline.

Reverse Gear The shift fork forces the first and reverse sliding gear backward until it engages with the reverse idler gear. The reverse idler gear allows the first and reverse sliding gear to rotate in the same direction as the reverse gear (20) on the countershaft. Powerflow now runs from the input shaft (2) to the input shaft gear (5) and countershaft-driven gear (6), then down the countershaft to gears 20 and 21. From the first/reverse sliding gear (18), torque is transferred to the mainshaft (16) and out to the driveline. Reverse Gear When reverse is selected, the shift lever is moved from neutral to reverse. The shift fork forces the first and reverse sliding gear backward (to the right) until it engages with the reverse idler gear (21). The reverse idler gear is required to allow the first and reverse sliding gear to rotate in the same direction as the reverse gear (20) on the countershaft. Powerflow (Figure 15– 8) now runs from the input shaft (2) to the input shaft gear (5) and countershaft-driven gear (6), then down the countershaft to gears 20 and 21. From the first/reverse sliding gear (18), torque is transferred to the mainshaft (16) and out to the driveline.

Collar Shift (1 of 7) In a collar-shifting arrangement, all gears on the countershaft are fixed to the countershaft. The mainshaft gears are free to freewheel (float) and do so around either a bearing or bushing. The mainshaft gears are in constant mesh with their mating countershaft gears. COLLAR SHIFT We can now take a closer look at collar-shift operation in the basic transmission first shown in Figure 15–16. This transmission uses collar shifting to control the engagement of second, third, fourth, and fifth gears. In a collar-shifting arrangement, all gears on the countershaft are fixed to the countershaft. On the other hand, the mainshaft gears are free to freewheel (float) and do so around either a bearing or bushing. These bearings or bushings are positioned on a nonsplined section of mainshaft. The mainshaft gears are in constant mesh with their mating countershaft gears. This means they turn at all times. Study the neutral power flow path of the five-speed transmission as shown in Figure 15–16. The input shaft (2) rotates at engine speed any time the clutch is engaged. The input shaft gear (5) is integral with the input (clutch) shaft, so it has to rotate with it. The input shaft gear meshes with the countershaft-driven gear (6), so it, the countershaft, and all the gears fixed to the countershaft also have to rotate. The countershaft gears transfer torque to their mating gears on the mainshaft. But mainshaft gears 8, 11, and 13 all freewheel on the mainshaft on bearings or bushings. Because they are freewheeling, they cannot

Collar Shift (2 of 7) The input shaft (2) rotates at engine speed any time the clutch is engaged. The input shaft gear (5) is integral with the input (clutch) shaft, so it has to rotate with it. The input shaft gear meshes with the countershaft-driven gear (6), the countershaft, and all the gears fixed to the countershaft also have to rotate. The countershaft gears transfer torque to their mating gears on the mainshaft. COLLAR SHIFT We can now take a closer look at collar-shift operation in the basic transmission first shown in Figure 15–16. This transmission uses collar shifting to control the engagement of second, third, fourth, and fifth gears. In a collar-shifting arrangement, all gears on the countershaft are fixed to the countershaft. On the other hand, the mainshaft gears are free to freewheel (float) and do so around either a bearing or bushing. These bearings or bushings are positioned on a nonsplined section of mainshaft. The mainshaft gears are in constant mesh with their mating countershaft gears. This means they turn at all times. Study the neutral power flow path of the five-speed transmission as shown in Figure 15–16. The input shaft (2) rotates at engine speed any time the clutch is engaged. The input shaft gear (5) is integral with the input (clutch) shaft, so it has to rotate with it. The input shaft gear meshes with the countershaft-driven gear (6), so it, the countershaft, and all the gears fixed to the countershaft also have to rotate. The countershaft gears transfer torque to their mating gears on the mainshaft. But mainshaft gears 8, 11, and 13 all freewheel on the mainshaft on bearings or bushings. Because they are freewheeling, they cannot

Collar Shift (3 of 7) But mainshaft gears 8, 11, and 13 all freewheel on the mainshaft. Because they are freewheeling, they cannot transmit torque to the mainshaft, so it does not turn. This means nothing is output to the driveline. To enable torque transfer to the mainshaft, one of the freewheeling mainshaft gears must be locked to it. COLLAR SHIFT We can now take a closer look at collar-shift operation in the basic transmission first shown in Figure 15–16. This transmission uses collar shifting to control the engagement of second, third, fourth, and fifth gears. In a collar-shifting arrangement, all gears on the countershaft are fixed to the countershaft. On the other hand, the mainshaft gears are free to freewheel (float) and do so around either a bearing or bushing. These bearings or bushings are positioned on a nonsplined section of mainshaft. The mainshaft gears are in constant mesh with their mating countershaft gears. This means they turn at all times. Study the neutral power flow path of the five-speed transmission as shown in Figure 15–16. The input shaft (2) rotates at engine speed any time the clutch is engaged. The input shaft gear (5) is integral with the input (clutch) shaft, so it has to rotate with it. The input shaft gear meshes with the countershaft-driven gear (6), so it, the countershaft, and all the gears fixed to the countershaft also have to rotate. The countershaft gears transfer torque to their mating gears on the mainshaft. But mainshaft gears 8, 11, and 13 all freewheel on the mainshaft on bearings or bushings. Because they are freewheeling, they cannot transmit torque to the mainshaft, so it does not turn. This means nothing is output to the driveline. To enable torque transfer to the mainshaft, one of the freewheeling mainshaft gears must be locked to it. This can be accomplished in a number of ways and one method uses a shift collar and shift gear. The shift gear is internally splined to the mainshaft at all times. The shift collar is splined to the shift gear. In Figure 15–19, you can see that the main gears have a short, toothed hub. The teeth on the main gear hub align with the teeth on the shift gear. The internal teeth of the shift collar mesh with the external teeth of the shift gear and hub. When a given speed range is not engaged, the shift collar simply rides on the shift gear. When the driver

Collar Shift (4 of 7) The shift gear is internally splined to the mainshaft at all times. The shift collar is splined to the shift gear. The main gears have a short, toothed hub. The teeth on the main gear hub align with the teeth on the shift gear. The internal teeth of the shift collar mesh with the external teeth of the shift gear and hub. COLLAR SHIFT We can now take a closer look at collar-shift operation in the basic transmission first shown in Figure 15–16. This transmission uses collar shifting to control the engagement of second, third, fourth, and fifth gears. In a collar-shifting arrangement, all gears on the countershaft are fixed to the countershaft. On the other hand, the mainshaft gears are free to freewheel (float) and do so around either a bearing or bushing. These bearings or bushings are positioned on a nonsplined section of mainshaft. The mainshaft gears are in constant mesh with their mating countershaft gears. This means they turn at all times. Study the neutral power flow path of the five-speed transmission as shown in Figure 15–16. The input shaft (2) rotates at engine speed any time the clutch is engaged. The input shaft gear (5) is integral with the input (clutch) shaft, so it has to rotate with it. The input shaft gear meshes with the countershaft-driven gear (6), so it, the countershaft, and all the gears fixed to the countershaft also have to rotate. The countershaft gears transfer torque to their mating gears on the mainshaft. But mainshaft gears 8, 11, and 13 all freewheel on the mainshaft on bearings or bushings. Because they are freewheeling, they cannot transmit torque to the mainshaft, so it does not turn. This means nothing is output to the driveline. To enable torque transfer to the mainshaft, one of the freewheeling mainshaft gears must be locked to it. This can be accomplished in a number of ways and one method uses a shift collar and shift gear. The shift gear is internally splined to the mainshaft at all times. The shift collar is splined to the shift gear. In Figure 15–19, you can see that the main gears have a short, toothed hub. The teeth on the main gear hub align with the teeth on the shift gear. The internal teeth of the shift collar mesh with the external teeth of the shift gear and hub. When a given speed range is not engaged, the shift collar simply rides on the shift gear. When the driver

Collar Shift (5 of 7) COLLAR SHIFT We can now take a closer look at collar-shift operation in the basic transmission first shown in Figure 15–16. This transmission uses collar shifting to control the engagement of second, third, fourth, and fifth gears. In a collar-shifting arrangement, all gears on the countershaft are fixed to the countershaft. On the other hand, the mainshaft gears are free to freewheel (float) and do so around either a bearing or bushing. These bearings or bushings are positioned on a nonsplined section of mainshaft. The mainshaft gears are in constant mesh with their mating countershaft gears. This means they turn at all times. Study the neutral power flow path of the five-speed transmission as shown in Figure 15–16. The input shaft (2) rotates at engine speed any time the clutch is engaged. The input shaft gear (5) is integral with the input (clutch) shaft, so it has to rotate with it. The input shaft gear meshes with the countershaft-driven gear (6), so it, the countershaft, and all the gears fixed to the countershaft also have to rotate. The countershaft gears transfer torque to their mating gears on the mainshaft. But mainshaft gears 8, 11, and 13 all freewheel on the mainshaft on bearings or bushings. Because they are freewheeling, they cannot transmit torque to the mainshaft, so it does not turn. This means nothing is output to the driveline. To enable torque transfer to the mainshaft, one of the freewheeling mainshaft gears must be locked to it. This can be accomplished in a number of ways and one method uses a shift collar and shift gear. The shift gear is internally splined to the mainshaft at all times. The shift collar is splined to the shift gear. In Figure 15–19, you can see that the main gears have a short, toothed hub. The teeth on the main gear hub align with the teeth on the shift gear. The internal teeth of the shift collar mesh with the external teeth of the shift gear and hub. When a given speed range is not engaged, the shift collar simply rides on the shift gear. When the driver shifts to engage that speed range, the shift fork moves the shift collar and slides it into mesh with the teeth of the main gear hub. At this moment, the shift collar rides on both the shift gear and main gear hub, locking them together. Power can flow from the main gear to the shift gear, then to the mainshaft and out to the propeller shaft. A second, more common method of locking main gears to the mainshaft does not use a shift gear. Instead, the shift collar is splined directly to the mainshaft. This shift collar, also called a clutch collar or a sliding clutch, is designed with external teeth. These external teeth mesh with internal teeth in the main gear hub or body when that speed range is engaged. Most shift collars or sliding clutches are positioned between two gears so they can control two-speed ranges depending on the direction in which they are moved by the shift fork (Figure 15–20). When a given speed range is not engaged, the shift collar simply rides on the shift gear. When the driver shifts to engage that speed range, the shift fork moves the shift collar and slides it into mesh with the teeth of the main gear hub. At this moment, the shift collar rides on both the shift gear and main gear hub, locking them together.

Collar Shift (6 of 7) Power can flow from the main gear to the shift gear, then to the mainshaft and out to the propeller shaft. A second, more common method of locking main gears to the mainshaft does not use a shift gear. Instead, the shift collar is splined directly to the mainshaft. This shift collar, also called a clutch collar or a sliding clutch, is designed with external teeth. COLLAR SHIFT We can now take a closer look at collar-shift operation in the basic transmission first shown in Figure 15–16. This transmission uses collar shifting to control the engagement of second, third, fourth, and fifth gears. In a collar-shifting arrangement, all gears on the countershaft are fixed to the countershaft. On the other hand, the mainshaft gears are free to freewheel (float) and do so around either a bearing or bushing. These bearings or bushings are positioned on a nonsplined section of mainshaft. The mainshaft gears are in constant mesh with their mating countershaft gears. This means they turn at all times. Study the neutral power flow path of the five-speed transmission as shown in Figure 15–16. The input shaft (2) rotates at engine speed any time the clutch is engaged. The input shaft gear (5) is integral with the input (clutch) shaft, so it has to rotate with it. The input shaft gear meshes with the countershaft-driven gear (6), so it, the countershaft, and all the gears fixed to the countershaft also have to rotate. The countershaft gears transfer torque to their mating gears on the mainshaft. But mainshaft gears 8, 11, and 13 all freewheel on the mainshaft on bearings or bushings. Because they are freewheeling, they cannot transmit torque to the mainshaft, so it does not turn. This means nothing is output to the driveline. To enable torque transfer to the mainshaft, one of the freewheeling mainshaft gears must be locked to it. This can be accomplished in a number of ways and one method uses a shift collar and shift gear. The shift gear is internally splined to the mainshaft at all times. The shift collar is splined to the shift gear. In Figure 15–19, you can see that the main gears have a short, toothed hub. The teeth on the main gear hub align with the teeth on the shift gear. The internal teeth of the shift collar mesh with the external teeth of the shift gear and hub. When a given speed range is not engaged, the shift collar simply rides on the shift gear. When the driver shifts to engage that speed range, the shift fork moves the shift collar and slides it into mesh with the teeth of the main gear hub. At this moment, the shift collar rides on both the shift gear and main gear hub, locking them together. Power can flow from the main gear to the shift gear, then to the mainshaft and out to the propeller shaft. A second, more common method of locking main gears to the mainshaft does not use a shift gear. Instead, the shift collar is splined directly to the mainshaft. This shift collar, also called a clutch collar or a sliding clutch, is designed with external teeth. These external teeth mesh with internal teeth in the main gear hub or body when that speed range is engaged. Most shift collars or sliding clutches are positioned between two gears so they can control two-speed ranges depending on the direction in which they are moved by the shift fork (Figure 15–20).

Collar Shift (7 of 7) These external teeth mesh with internal teeth in the main gear hub or body when that speed range is engaged. Most shift collars or sliding clutches are positioned between two gears so they can control two-speed ranges depending on the direction in which they are moved by the shift fork COLLAR SHIFT We can now take a closer look at collar-shift operation in the basic transmission first shown in Figure 15–16. This transmission uses collar shifting to control the engagement of second, third, fourth, and fifth gears. In a collar-shifting arrangement, all gears on the countershaft are fixed to the countershaft. On the other hand, the mainshaft gears are free to freewheel (float) and do so around either a bearing or bushing. These bearings or bushings are positioned on a nonsplined section of mainshaft. The mainshaft gears are in constant mesh with their mating countershaft gears. This means they turn at all times. Study the neutral power flow path of the five-speed transmission as shown in Figure 15–16. The input shaft (2) rotates at engine speed any time the clutch is engaged. The input shaft gear (5) is integral with the input (clutch) shaft, so it has to rotate with it. The input shaft gear meshes with the countershaft-driven gear (6), so it, the countershaft, and all the gears fixed to the countershaft also have to rotate. The countershaft gears transfer torque to their mating gears on the mainshaft. But mainshaft gears 8, 11, and 13 all freewheel on the mainshaft on bearings or bushings. Because they are freewheeling, they cannot transmit torque to the mainshaft, so it does not turn. This means nothing is output to the driveline. To enable torque transfer to the mainshaft, one of the freewheeling mainshaft gears must be locked to it. This can be accomplished in a number of ways and one method uses a shift collar and shift gear. The shift gear is internally splined to the mainshaft at all times. The shift collar is splined to the shift gear. In Figure 15–19, you can see that the main gears have a short, toothed hub. The teeth on the main gear hub align with the teeth on the shift gear. The internal teeth of the shift collar mesh with the external teeth of the shift gear and hub. When a given speed range is not engaged, the shift collar simply rides on the shift gear. When the driver shifts to engage that speed range, the shift fork moves the shift collar and slides it into mesh with the teeth of the main gear hub. At this moment, the shift collar rides on both the shift gear and main gear hub, locking them together. Power can flow from the main gear to the shift gear, then to the mainshaft and out to the propeller shaft. A second, more common method of locking main gears to the mainshaft does not use a shift gear. Instead, the shift collar is splined directly to the mainshaft. This shift collar, also called a clutch collar or a sliding clutch, is designed with external teeth. These external teeth mesh with internal teeth in the main gear hub or body when that speed range is engaged. Most shift collars or sliding clutches are positioned between two gears so they can control two-speed ranges depending on the direction in which they are moved by the shift fork (Figure 15–20).

Third Gear Power Flow Moving from neutral to third gear moves the second and third shift collar (or sliding clutch) (12) forward toward the third gear (11), locking it to the mainshaft. Power flows from 2 to 5 and 6, along the countershaft to 10, up to 11, through the shift collar (12) to the mainshaft and out to the driveline Third Gear Power Flow Once again the driver returns to neutral before shifting to third gear. Moving from neutral to third gear moves the second and third shift collar (or sliding clutch) (12) forward toward the third gear (11), locking it to the mainshaft. Power flows from 2 to 5 and 6, along the countershaft to 10, up to 11, through the shift collar (12) to the mainshaft and out to the driveline (Figure 15–22).

Fourth Gear Power Flow After shifting from third to neutral, the neutral to fourth gearshift causes the shifter fork to move the fourth and fifth shift collar (or sliding clutch 7) into mesh with the fourth gear (8). Power now flows from 2 to 5 and 6, along the countershaft to 9, through 8 and 7 to the mainshaft, and out to the driveline Fourth Gear Power Flow After shifting from third to neutral, the neutral to fourth gearshift causes the shifter fork to move the fourth and fifth shift collar (or sliding clutch 7) into mesh with the fourth gear (8). Power now flows from 2 to 5 and 6, along the countershaft to 9, through 8 and 7 to the mainshaft, and out to the driveline (Figure 15–23).

Fifth Gear Power Flow The shifter fork moves the fourth and fifth shift collar (or sliding clutch 7) into mesh with the input shaft gear (5). This locks the input shaft (2) directly to the mainshaft (16). Input and output speeds are the same. The power flow is from 2 to 5 through 7, then to the mainshaft and out. The countershaft and its gears are all turning. The mainshaft gears 8, 11, and 13 are also freewheeling on the mainshaft, but have no effect on the powerflow. Fifth Gear Power Flow Shifting from fourth to neutral, then from neutral to the fifth gear, causes the shifter fork to move the fourth and fifth shift collar (or sliding clutch 7) into mesh with the input shaft gear (5). This locks the input shaft (2) directly to the mainshaft (16). Input and output speeds are the same. So a 1:1 gear ratio is established. The power flow (Figure 15–24) is from 2 to 5 through 7, then to the mainshaft and out. In fifth gear the clutch shaft gear is still meshed with the countershaft-driven gear (6). This means that the countershaft and its gears are all turning. The mainshaft gears 8, 11, and 13 are also freewheeling on the mainshaft but have no effect on the powerflow. Take some time to study the power flow schematics shown in Figures 15–16 through 15–24. Knowing the power flow paths through the transmission you are working on can make diagnosis and failure analysis much easier.

Shop Talk The clutch brake is used to stop gear rotation in order to complete a shift into first or reverse when the vehicle is stationary. The clutch brake is actuated by depressing the clutch pedal completely to the floor. For normal upshifts and downshifts, only partial disengagement of the clutch is needed to break engine torque. The 750 rpm drop used in the description of shifting procedure varies according to engine-governed speed and torque rise profile. Shop Talk As explained in Chapter 9, a clutch brake is used to stop gear rotation in order to complete a shift into first or reverse when the vehicle is stationary. The clutch brake is actuated by depressing the clutch pedal completely to the floor. For normal upshifts and downshifts, only partial disengagement of the clutch is needed to break engine torque; in other words, it is not necessary to drive the clutch pedal to the floor to shift. The 750 rpm drop used in the description of shifting procedure varies according to engine-governed speed and torque rise profile.

Block or Cone Synchronizers (1 of 4)
The synchronizer sleeve is splined to the clutch hub. The clutch hub is also splined to the transmission output (main) shaft. The synchronizer sleeve has a small internal groove and a large external groove in which the shift fork rests. Three slots are equally spaced around the outside of the clutch hub. Block or Cone Synchronizers Figure 15–25 illustrates a block or cone synchronizer. The synchronizer sleeve surrounds the synchronizer assembly and meshes with the external splines of the clutch hub. The clutch hub is splined to the transmission output (main) shaft and is held in position by two snap-rings. The synchronizer sleeve has a small internal groove and a large external groove in which the shift fork rests. Three slots are equally spaced around the outside of the clutch hub. Inserts fit into these slots and are able to slide freely back and forth. These inserts are designed with a ridge in their outer surface. Insert springs hold the ridge in contact with the synchronizer sleeve internal groove.

Inserts fit into these slots and are able to slide freely back and forth. These inserts are designed with a ridge in their outer surface. Insert springs hold the ridge in contact with the synchronizer sleeve internal groove. Block or Cone Synchronizers Figure 15–25 illustrates a block or cone synchronizer. The synchronizer sleeve surrounds the synchronizer assembly and meshes with the external splines of the clutch hub. The clutch hub is splined to the transmission output (main) shaft and is held in position by two snap-rings. The synchronizer sleeve has a small internal groove and a large external groove in which the shift fork rests. Three slots are equally spaced around the outside of the clutch hub. Inserts fit into these slots and are able to slide freely back and forth. These inserts are designed with a ridge in their outer surface. Insert springs hold the ridge in contact with the synchronizer sleeve internal groove. The synchronizer sleeve is precisely machined to slide on the clutch hub smoothly. The sleeve and hub sometimes have alignment marks to ensure proper indexing of their splines when assembling to maintain smooth operation. Brass or bronze synchronizing blocker rings are positioned at the front and rear of each synchronizer assembly. Each blocker ring has three notches equally spaced to correspond with the three inset notches of the hub. Around the outside of each blocker ring is a set of beveled dog teeth, which are used for alignment during the shift sequence. The inside of the blocker ring is shaped like a cone. This coned surface is lined with many sharp grooves. The cone of the blocker ring makes up one-half of a cone clutch assembly. The second or mating half of the cone clutch is part of the gear to be synchronized. As you can see in Figure 15–26, the shoulder of the main gear is cone shaped to match the blocker ring. The shoulder also contains a ring of beveled dog teeth designed to align with dog teeth on the blocker ring.

Brass or bronze synchronizing blocker rings are positioned at the front and rear of each synchronizer assembly. Each blocker ring has three notches equally spaced to correspond with the three inset notches of the hub. Around the outside of each blocker ring is a set of beveled dog teeth, which are used for alignment during the shift sequence. The inside of the blocker ring is shaped like a cone. Block or Cone Synchronizers Figure 15–25 illustrates a block or cone synchronizer. The synchronizer sleeve surrounds the synchronizer assembly and meshes with the external splines of the clutch hub. The clutch hub is splined to the transmission output (main) shaft and is held in position by two snap-rings. The synchronizer sleeve has a small internal groove and a large external groove in which the shift fork rests. Three slots are equally spaced around the outside of the clutch hub. Inserts fit into these slots and are able to slide freely back and forth. These inserts are designed with a ridge in their outer surface. Insert springs hold the ridge in contact with the synchronizer sleeve internal groove. The synchronizer sleeve is precisely machined to slide on the clutch hub smoothly. The sleeve and hub sometimes have alignment marks to ensure proper indexing of their splines when assembling to maintain smooth operation. Brass or bronze synchronizing blocker rings are positioned at the front and rear of each synchronizer assembly. Each blocker ring has three notches equally spaced to correspond with the three inset notches of the hub. Around the outside of each blocker ring is a set of beveled dog teeth, which are used for alignment during the shift sequence. The inside of the blocker ring is shaped like a cone. This coned surface is lined with many sharp grooves. The cone of the blocker ring makes up one-half of a cone clutch assembly. The second or mating half of the cone clutch is part of the gear to be synchronized. As you can see in Figure 15–26, the shoulder of the main gear is cone shaped to match the blocker ring. The shoulder also contains a ring of beveled dog teeth designed to align with dog teeth on the blocker ring.

This coned surface is lined with many sharp grooves. The cone of the blocker ring makes up one-half of a cone clutch assembly. The second or mating half of the cone clutch is part of the gear to be synchronized. The shoulder of the main gear is cone shaped to match the blocker ring. The shoulder also contains a ring of beveled dog teeth designed to align with dog teeth on the blocker ring. Block or Cone Synchronizers Figure 15–25 illustrates a block or cone synchronizer. The synchronizer sleeve surrounds the synchronizer assembly and meshes with the external splines of the clutch hub. The clutch hub is splined to the transmission output (main) shaft and is held in position by two snap-rings. The synchronizer sleeve has a small internal groove and a large external groove in which the shift fork rests. Three slots are equally spaced around the outside of the clutch hub. Inserts fit into these slots and are able to slide freely back and forth. These inserts are designed with a ridge in their outer surface. Insert springs hold the ridge in contact with the synchronizer sleeve internal groove. The synchronizer sleeve is precisely machined to slide on the clutch hub smoothly. The sleeve and hub sometimes have alignment marks to ensure proper indexing of their splines when assembling to maintain smooth operation. Brass or bronze synchronizing blocker rings are positioned at the front and rear of each synchronizer assembly. Each blocker ring has three notches equally spaced to correspond with the three inset notches of the hub. Around the outside of each blocker ring is a set of beveled dog teeth, which are used for alignment during the shift sequence. The inside of the blocker ring is shaped like a cone. This coned surface is lined with many sharp grooves. The cone of the blocker ring makes up one-half of a cone clutch assembly. The second or mating half of the cone clutch is part of the gear to be synchronized. As you can see in Figure 15–26, the shoulder of the main gear is cone shaped to match the blocker ring. The shoulder also contains a ring of beveled dog teeth designed to align with dog teeth on the blocker ring.

Plain Synchronizers It is like a block synchronizer with fewer parts.
The hub is internally splined to the mainshaft. Mounted on the hub is a sliding sleeve controlled by the shift fork movement. The friction generated between the hub and the gear synchronizes the speeds. Pressure on the sliding sleeve prevents it from engaging the gear teeth until sufficient pressure has caused synchronization. The sleeve teeth then engage the gear teeth. PLAIN SYNCHRONIZERS A plain synchronizer uses fewer working parts and is similar in design to a block synchronizer (Figure 15–30). As is typical with most synchronizers, the hub is internally splined to the mainshaft. Mounted on the hub, and also connected to it, is a sliding sleeve that is controlled by the shift fork movement. In operation, the friction generated between the hub and the gear tends to synchronize their speeds. Pressure on the sliding sleeve prevents the sleeve from moving off the hub and also prevents the teeth on the sleeve from engaging the gear teeth until sufficient pressure has been put on both friction areas to synchronize the components. When in sync, any further movement of the sleeve will allow the sleeve teeth to engage the gear teeth.

Shift Bar Housing (1 of 2) The shift bar housing contains the components required to convert gear stick movement into shifts within the transmission. This is an exploded view of a typical shift bar housing assembly such as one commonly used for five-speed main box. This transmission is usually coupled to an auxiliary box or compound (used to multiply the number of available gear ratios). SHIFT BAR HOUSING The shift bar housing, also known as the shift rail assembly, houses the components required to convert gear stick movement into range gearshifts within the transmission. There are some design variations between manufacturers but what you see in Figure 15–33 is typical; this figure is an exploded view of a shift bar housing used in a seven-speed transmission. Figure 15–34 illustrates the shift bar housing assembly used in a commonly used five-speed main box; this transmission is usually coupled to an auxiliary box or compound (used to multiply the number of available gear ratios).

Shift Bar Housing (2 of 2) SHIFT BAR HOUSING
The shift bar housing, also known as the shift rail assembly, houses the components required to convert gear stick movement into range gearshifts within the transmission. There are some design variations between manufacturers but what you see in Figure 15–33 is typical; this figure is an exploded view of a shift bar housing used in a seven-speed transmission. Figure 15–34 illustrates the shift bar housing assembly used in a commonly used five-speed main box; this transmission is usually coupled to an auxiliary box or compound (used to multiply the number of available gear ratios).

Operation (1 of 2) After a shift has been effected, the shift bar must be held in position with a detent mechanism. The detent mechanism consists of a spring-loaded detent steel ball or poppet. The spring loads the steel ball into the recess in the shift bar. The detent ball holds the shift bar in position and prevents unwanted movement of the other bars. OPERATION The gearshift lever in a direct shift tower arrangement, or the remote-actuated shift finger in a COE application, fits into slots formed by the shift bracket or yoke blocks. If you take a look at Figure 15–33 and Figure 15–34, the shift brackets or blocks can either be clamped to a shift rail or integral with the shift fork or yoke. The shift bars or rails are designed to slide in the shift bar housing when actuated by the gear lever. The shift forks or yokes are clamped or bolted to the shift bars. When the gearshift lever is moved, it slides the shift bars and thereby moves the yokes: The shift yoke fits over a shift collar or synchronizer so an actual shift can be made. After a shift has been effected, the shift bar must be held in position so that the selected gear ratio is maintained. To hold the selected gear and prevent unwanted rail movement, the shift bars are machined with recesses; these recesses align with a detent mechanism. The detent mechanism consists of a spring-loaded detent steel ball or poppet: The spring loads the steel ball into the recess in the shift bar. The detent ball holds the shift bar in position and prevents unwanted movement of the other bars. When the driver makes a shift, he must overcome the spring pressure of the detent ball to move the shift bar.

Operation (2 of 2) OPERATION
The gearshift lever in a direct shift tower arrangement, or the remote-actuated shift finger in a COE application, fits into slots formed by the shift bracket or yoke blocks. If you take a look at Figure 15–33 and Figure 15–34, the shift brackets or blocks can either be clamped to a shift rail or integral with the shift fork or yoke. The shift bars or rails are designed to slide in the shift bar housing when actuated by the gear lever. The shift forks or yokes are clamped or bolted to the shift bars. When the gearshift lever is moved, it slides the shift bars and thereby moves the yokes: The shift yoke fits over a shift collar or synchronizer so an actual shift can be made. After a shift has been effected, the shift bar must be held in position so that the selected gear ratio is maintained. To hold the selected gear and prevent unwanted rail movement, the shift bars are machined with recesses; these recesses align with a detent mechanism. The detent mechanism consists of a spring-loaded detent steel ball or poppet: The spring loads the steel ball into the recess in the shift bar. The detent ball holds the shift bar in position and prevents unwanted movement of the other bars. When the driver makes a shift, he must overcome the spring pressure of the detent ball to move the shift bar.

Shop Talk In troubleshooting a transmission complaint of slipping out of gear, one of the first things you should check is the detent assemblies. Broken springs and seized detent balls can result in unwanted shift rail movement.

Twin Countershaft Transmissions (1 of 3)
Most heavy-duty truck standard transmissions are compounded, usually with a single auxiliary section. Some have a main box and two auxiliary sections. Twin countershaft transmissions having nine to eighteen forward speed ranges are among the more common heavy-duty truck transmissions. COUNTERSHAFT TRANSMISSIONS Now that the basics of gears, shift mechanisms, and power flow have been discussed, a closer examination of countershaft transmissions equipped with both a main and auxiliary gear section should follow. Most heavy-duty truck standard transmissions are compounded, usually with a single auxiliary section. Some have a main box and two auxiliary sections. Twin-countershaft transmissions having nine to eighteen forward speed ranges are among the more common heavy-duty truck transmissions. The Eaton Roadranger transmission has been dominant in heavy truck applications for many years and this uses a twin-countershaft design as do most of its competitors. The exception is Mack Trucks triple-countershaft design, but even with this transmission most of the operating principles of the twin-countershaft transmission apply.

The countershafts on either side of the transmission split input torque equally. Because of this, the face width of the gears can be narrower. The mainshaft gears float between the countershaft gears when disengaged, eliminating the need for gear bushings or sleeves. When disengaged, the mainshaft gears freewheel around the mainshaft because they are in constant mesh with the countershaft drive gears. Figure 15–35 shows a simplified twin-countershaft transmission for purposes of demonstrating some of the principles we are going to discuss. The gear sets on either side of the transmission split input torque equally. This means that each countershaft has to carry only half the torque load that a single-countershaft transmission would be subjected to. Because of this, the face width of the gears can be narrower than that of those used in a single-countershaft transmission. Additionally, the mainshaft gears float between the countershaft gears when disengaged, eliminating the need for gear bushings or sleeves. Transmissions that use the twin-countershaft design typically use spur gears in constant mesh. When disengaged, the mainshaft gears freewheel around the mainshaft because they are in constant mesh with the countershaft drive gears. The motion is not transferred to the actual shaft itself, however, until the sliding clutch gear is moved into engagement. The output shaft will then turn at the same speed as the mainshaft gear. The sliding clutch gear that engages with the mainshaft gear is typically splined to the mainshaft.

The motion is not transferred to the actual shaft itself, however, until the sliding clutch gear is moved into engagement. The output shaft will then turn at the same speed as the mainshaft gear. The sliding clutch gear that engages with the mainshaft gear is typically splined to the mainshaft. Figure 15–35 shows a simplified twin-countershaft transmission for purposes of demonstrating some of the principles we are going to discuss. The gear sets on either side of the transmission split input torque equally. This means that each countershaft has to carry only half the torque load that a single-countershaft transmission would be subjected to. Because of this, the face width of the gears can be narrower than that of those used in a single-countershaft transmission. Additionally, the mainshaft gears float between the countershaft gears when disengaged, eliminating the need for gear bushings or sleeves. Transmissions that use the twin-countershaft design typically use spur gears in constant mesh. When disengaged, the mainshaft gears freewheel around the mainshaft because they are in constant mesh with the countershaft drive gears. The motion is not transferred to the actual shaft itself, however, until the sliding clutch gear is moved into engagement. The output shaft will then turn at the same speed as the mainshaft gear. The sliding clutch gear that engages with the mainshaft gear is typically splined to the mainshaft.

Powerflow in Low Range The input shaft and drive gear are in constant mesh with both countershaft drive gears. The countershaft gears are in constant mesh with the floating mainshaft gears. The mainshaft gears freewheel on the mainshaft. A sliding clutch gear splined to the mainshaft is engaged into the internal clutching teeth of the mainshaft gear, coupling it to the mainshaft. The mainshaft will now be turning at the selected gear ratio. Figure 15–36 shows a twin-countershaft transmission that looks more like something you would see in a truck; it illustrates the powerflow through the transmission when in low range. Note how the torque path is split. The input shaft and drive gear (1) are in constant mesh with both countershaft drive gears (2); whenever the input shaft turns, the countershafts must also turn. The countershaft gears are in constant mesh with the floating mainshaft gears (3). The mainshaft gears freewheel on the mainshaft (4). A sliding clutch gear (5), splined to the mainshaft, is engaged into the internal clutching teeth of the mainshaft gear, coupling it to the mainshaft. The mainshaft will now be turning at the selected gear ratio.

5 Speed Main + Auxiliary Two- or three-speed auxiliary section
Main shifted manually Auxiliary air shifted Selection of the gears in the auxiliary section is made by a driver-actuated, air-operated piston. The driver uses a pneumatic switch, usually located on the gear lever, that moves the auxiliary section into low- or high-range ratios. The driver controls this range selection mechanism through the use of a master control valve switch mounted on the gearshift tower in the operating cab. AUXILIARY GEAR SECTIONS Countershaft transmissions having eight or more forward speeds typically consist of a five-speed main section or box and a two- or three-speed auxiliary section. The main and auxiliary gearing can be contained in a single housing or each section can have separate casings that are coupled to each other. The auxiliary gearing is usually located behind the main box. The main box shown in the ten-speed transmission shown in Figure 15–36 has a five-speed ratio; the auxiliary section that couples to it has two ranges or speeds. There is a direct (or high) range and a low range in this transmission. Shifts in the main section are effected mechanically by the driver using the shift stick. However, selection of the gears in the auxiliary section is made by a driver-actuated, air-operated piston. The driver uses a pneumatic switch, usually located on the gear lever, that moves the auxiliary section into low- or high-range ratios. The driver controls this range selection mechanism through the use of a master control valve switch mounted on the gearshift tower in the operating cab. Follow the power flow through the transmission in Figure 15–36; it is operating in low range. The following is true: Torque from the engine flywheel is transmitted to the transmission input shaft. Splines on the input shaft mesh with internal splines in the hub of the drive gear. Torque is split between the two countershaft drive gears that mesh with the mainshaft drive gear. Torque is transferred by the two countershaft gears to whichever mainshaft gear is engaged. Figure 15–36 shows first gear engagement. Shifting and power flows in the main section are similar to those in the five-speed transmission discussed earlier in this chapter under the heading Mechanical Shift Mechanisms. A notable difference is the use of a PTO (power takeoff) gear located between the countershaft drive gears and fourth gears. Internal splines in the hub of the mainshaft gear transfer torque to the mainshaft by means of a sliding clutch gear. The mainshaft transfers torque to the auxiliary drive gear through a self-aligning coupling gear located in the hub of the auxiliary drive gear. Torque is split between the two auxiliary countershaft drive gears. Torque is delivered by the two countershaft low-range gears to the auxiliary low-range gear. Torque is transfered to the output shaft through a self-aligning sliding clutch gear that locks the low-range gear to the output shaft. The output shaft connects by means of a yoke to the driveline. Figure 15–37 shows the same transmission when power is directed through the high-range (direct-drive) gearing of the auxiliary section. In this range, the sliding clutch gear locks the auxiliary drive gear to the output shaft. The low-range gear on the output shaft is now allowed to freewheel. The ten forward speeds are selected by using a five speed shifting pattern twice, the first time with the auxiliary section engaged in low gear or low range; the second time engaged in high gear or high range. By using the same shifting pattern twice, the shift lever position for sixth speed is the same as first, seventh the same as second, eighth the same as third, ninth the same as fourth, and tenth the same as fifth. Figure 15–38 illustrates the gearshift lever pattern and range control button positions for this model transmission.

Auxiliary Gear Sections (1 of 2)
Power is directed through the high-range (direct-drive) gearing of the auxiliary section. In this range, the sliding clutch gear locks the auxiliary drive gear to the output shaft. The low-range gear on the output shaft is now allowed to freewheel. The five-speed shifting pattern is used twice–the first time with the auxiliary section engaged in low gear or low range; the second time engaged in high gear or high range. Figure 15–37 shows the same transmission when power is directed through the high-range (direct-drive) gearing of the auxiliary section. In this range, the sliding clutch gear locks the auxiliary drive gear to the output shaft. The low-range gear on the output shaft is now allowed to freewheel. The ten forward speeds are selected by using a five speed shifting pattern twice, the first time with the auxiliary section engaged in low gear or low range; the second time engaged in high gear or high range. By using the same shifting pattern twice, the shift lever position for sixth speed is the same as first, seventh the same as second, eighth the same as third, ninth the same as fourth, and tenth the same as fifth. Figure 15–38 illustrates the gearshift lever pattern and range control button positions for this model transmission.

Auxiliary Gear Sections (2 of 2)
By using the same shifting pattern twice, the shift lever position for sixth speed is the same as first, seventh the same as second, eighth the same as third, ninth the same as fourth, and tenth the same as fifth. This illustrates the gearshift lever pattern and range control button positions for this model transmission. Figure 15–37 shows the same transmission when power is directed through the high-range (direct-drive) gearing of the auxiliary section. In this range, the sliding clutch gear locks the auxiliary drive gear to the output shaft. The low-range gear on the output shaft is now allowed to freewheel. The ten forward speeds are selected by using a five speed shifting pattern twice, the first time with the auxiliary section engaged in low gear or low range; the second time engaged in high gear or high range. By using the same shifting pattern twice, the shift lever position for sixth speed is the same as first, seventh the same as second, eighth the same as third, ninth the same as fourth, and tenth the same as fifth. Figure 15–38 illustrates the gearshift lever pattern and range control button positions for this model transmission.

High-/Low-Range Shift Systems
An air-operated auxiliary section gearshift system consists of the following: Air filter/regulator Slave valve Master control valve Range cylinder Fittings and connecting air lines HIGH/LOW RANGE SHIFT SYSTEMS An air-operated auxiliary section gearshift system consists of the following: • Air filter/regulator • Slave valve • Master control valve • Range cylinder • Fittings and connecting air lines Figure 15–39 illustrates a typical air-operated gearshift control system used to engage high- and low-range gearing in the auxiliary section. Note the location of the range and splitter cylinders and how they connect with the control pneumatics. Air Filter/Regulator The air filter/regulator assembly (Figure 15–40) minimizes the possibility of moisture-laden air or impurities from entering the system. The regulator is used to reduce chassis system air-supply pressure to the range valve and the slave valve. If you follow the air plumbing shown in Figure 15–41, you can see that

Air System Figure 15–39 illustrates a typical air-operated gearshift control system used to engage high- and low-range gearing in the auxiliary section. Note the location of the range and splitter cylinders and how they connect with the control pneumatics. A typical air-operated gearshift control system used to engage high- and low-range gearing in the auxiliary section Note the location of the range and splitter cylinders and how they connect with the control pneumatics.

Air Filter/Regulator The air filter/regulator assembly:
Minimizes the possibility of moisture-laden air or impurities from entering the system Reduces chassis system air-supply pressure to the range valve and the slave valve Air Filter/Regulator The air filter/regulator assembly (Figure 15–40) minimizes the possibility of moisture-laden air or impurities from entering the system. The regulator is used to reduce chassis system air-supply pressure to the range valve and the slave valve. If you follow the air plumbing shown in Figure 15–41, you can see that

Range Air System (1 of 3) If you follow the air plumbing shown in Figure 15–41, you can see that air from the chassis air system is supplied to the air supply port on the air regulator. When filtered, the air is then routed to the air regulator. Transmission air pressure is typically regulated at between 57 and 62 psi. Next, the air passes through the 1/4-inch supply air line and 1/8-inch OD (overdrive) range valve supply air line to the supply ports of the slave valve and range valve. Depending on the position of the gear shift–mounted range valve, air will pass through either the low-range air line or the high-range air line to the range shift cylinder. Range shifts can be made only when the gearshift lever is in, or passing through, neutral. This means that the driver can preselect a range shift while in gear. As the gear lever is moved through neutral, the actuating plunger in the shift bar housing releases the slave valve, allowing it to move to the selected range position. Filtered: Air from the chassis air system is supplied to the air supply port on the air regulator. Regulated: When filtered, the air is then routed to the air regulator. Transmission air pressure is typically regulated at between 57 and 62 psi.

Range Air System (2 of 3) Slave valve: Next, the air passes through the 1/4-inch supply air line and 1/8-inch OD (overdrive) range valve supply air line to the supply ports of the slave valve and range valve. Range valve: Depending on the position of the gear shift-mounted range valve, air will pass through either the low-range air line or the high-range air line to the range shift cylinder. If you follow the air plumbing shown in Figure 15–41, you can see that air from the chassis air system is supplied to the air supply port on the air regulator. When filtered, the air is then routed to the air regulator. Transmission air pressure is typically regulated at between 57 and 62 psi. Next, the air passes through the 1/4-inch supply air line and 1/8-inch OD (overdrive) range valve supply air line to the supply ports of the slave valve and range valve. Depending on the position of the gear shift–mounted range valve, air will pass through either the low-range air line or the high-range air line to the range shift cylinder. Range shifts can be made only when the gearshift lever is in, or passing through, neutral. This means that the driver can preselect a range shift while in gear. As the gear lever is moved through neutral, the actuating plunger in the shift bar housing releases the slave valve, allowing it to move to the selected range position.

Range Air System (3 of 3) Pre-selecting: Range shifts can be made only when the gearshift lever is in, or passing through, neutral. The driver can pre-select a range shift while in gear. Actuating plunger: As the gear lever is moved through neutral, the actuating plunger in the shift bar housing releases the slave valve, allowing it to move to the selected range position. If you follow the air plumbing shown in Figure 15–41, you can see that air from the chassis air system is supplied to the air supply port on the air regulator. When filtered, the air is then routed to the air regulator. Transmission air pressure is typically regulated at between 57 and 62 psi. Next, the air passes through the 1/4-inch supply air line and 1/8-inch OD (overdrive) range valve supply air line to the supply ports of the slave valve and range valve. Depending on the position of the gear shift–mounted range valve, air will pass through either the low-range air line or the high-range air line to the range shift cylinder. Range shifts can be made only when the gearshift lever is in, or passing through, neutral. This means that the driver can preselect a range shift while in gear. As the gear lever is moved through neutral, the actuating plunger in the shift bar housing releases the slave valve, allowing it to move to the selected range position.

Slave Valve The slave valve can be of the piston or poppet type.
The slave valve (Figure 15–42) can be of the piston or poppet type. The slave valve distributes inlet air pressure to both the low- and high-range air circuits that connect to the range cylinder. The piston (or plunger) controls when and where transmission air pressure is distributed. Slave valve operation (low range and high range) is illustrated in Figure 15–43 and Figure 15–44. An air valve shaft protruding from the shift bar housing prevents the actuating piston in the slave valve from moving while the gear shift lever is in any gear position: It releases the piston when the lever is moved to or through neutral (Figure 15–45). The slave valve can be of the piston or poppet type. The slave valve distributes inlet air pressure to both the low- and high-range air circuits The piston controls when and where air pressure is distributed.

Slave Valve In Low Range
The slave valve (Figure 15–42) can be of the piston or poppet type. The slave valve distributes inlet air pressure to both the low- and high-range air circuits that connect to the range cylinder. The piston (or plunger) controls when and where transmission air pressure is distributed. Slave valve operation (low range and high range) is illustrated in Figure 15–43 and Figure 15–44. An air valve shaft protruding from the shift bar housing prevents the actuating piston in the slave valve from moving while the gear shift lever is in any gear position: It releases the piston when the lever is moved to or through neutral (Figure 15–45). Slave valve operation in low range is illustrated. An air valve shaft protruding from the shift bar housing prevents the actuating piston in the slave valve from moving while the gear shift lever is in any gear position.

Slave Valve in High Range
The slave valve (Figure 15–42) can be of the piston or poppet type. The slave valve distributes inlet air pressure to both the low- and high-range air circuits that connect to the range cylinder. The piston (or plunger) controls when and where transmission air pressure is distributed. Slave valve operation (low range and high range) is illustrated in Figure 15–43 and Figure 15–44. An air valve shaft protruding from the shift bar housing prevents the actuating piston in the slave valve from moving while the gear shift lever is in any gear position: It releases the piston when the lever is moved to or through neutral (Figure 15–45). Slave valve operation in high range is illustrated. An air valve shaft protruding from the shift bar housing prevents the actuating piston in the slave valve from moving while the gear shift lever is in any gear position.

Slave Valve In Neutral Position
The slave valve (Figure 15–42) can be of the piston or poppet type. The slave valve distributes inlet air pressure to both the low- and high-range air circuits that connect to the range cylinder. The piston (or plunger) controls when and where transmission air pressure is distributed. Slave valve operation (low range and high range) is illustrated in Figure 15–43 and Figure 15–44. An air valve shaft protruding from the shift bar housing prevents the actuating piston in the slave valve from moving while the gear shift lever is in any gear position: It releases the piston when the lever is moved to or through neutral (Figure 15–45).

Range Valve Constant air pressure is supplied to the inlet port.
In low range, this air passes through the valve and is routed to the slave valve end cap or P-port. In high range (control switch up), the valve slide prevents the air from passing through the range valve. Air pressure that was in the outlet line is now exhausted. This means that the transmission defaults to high range. Range Valve The master control valve is sometimes referred to as the range valve. Constant air pressure is supplied to the inlet port of the range valve (Figure 15–47) by the slave valve. In low range (control switch down), air routes through the valve slide and exits the outlet port. This air returns to the slave valve to the end port (or P-port), depending on the type of slave valve used. In high range (control switch up), the valve slide prevents the air from passing through the range valve. Air pressure that was in the outlet line is now exhausted out the bottom of the range valve. This means that the transmission defaults to high range.

Split Shifting A typical splitter air system is equipped with both the high/low range selector and splitter selector mounted on the gear shift lever. The splitter gear system in a thirteen-gear transmission is used only while in high range and splits the high-range gearing into either direct or overdrive ratios. Splitter systems used on eighteen-gear transmissions are used to split both high- and low-range gearing. Split Shifting The third gear of the auxiliary section is engaged or disengaged from the power flow by means of an airactivated splitter shift system. The splitter control button is located on the gear lever. Figure 15–48 illustrates a typical splitter air system equipped with both the high/low range selector and splitter selector mounted on the gear shift lever. The system shown is used on typical thirteen-speed overdrive or underdrive transmissions. The splitter gear system in a thirteen- gear transmission is used only while in high range and splits the high-range gearing either into overdrive or underdrive ratios depending on the transmission model. Splitter systems used on eighteen gear transmissions are used to split both high- and low-range gearing.

Splitter Cylinder Constant air is supplied to the splitter cover and acts on the front side of the piston. An insert valve directs the air. In overdrive, air is routed through the shift tower valve and is supplied to the left port of the cylinder cover. In direct, the S-port of the shift tower valve is closed and no air is supplied to the left port of the splitter cylinder cover. Splitter Cylinder Operation In a basic splitter system, constant air from the air filter/regulator assembly is supplied to the splitter cylinder through a port on the cylinder cover (see Figure 15–39). This air supply acts on the front side of the shift piston in the cylinder. An insert valve installed in the cover provides the air required to move the splitter piston either forward or rearward. This movement is transferred to the yoke or shift fork bar and onto the shift fork (Figure 15–49). The movement of the yoke or shift fork engages a sliding clutch, which in turn locks the third auxiliary gear to the main output shaft. When operating in either the high or low range, the air required to make the splitter selection is supplied to the gearshift lever valve (Figure 15–50) from the fitting at the S-port of the slave valve mounted on the transmission housing. When an overdrive (button forward) selection is made (Figure 15–51A), air is routed through the shift tower valve and is supplied to the left port of the cylinder cover of the splitter cylinder. When the splitter control button on the shift tower is in the direct or rear position (Figure 15–51B), the S-port of the shift tower valve is closed and no air is supplied to the left port of the splitter cylinder cover.

Eighteen-speed Transmissions (1 of 2)
Figure 15–52 illustrates a transmission with eighteen forward speeds. The main or front gearing is a five speed transmission. In this particular transmission, main gears are referred to as low, first, second, third, and drive, rather than first, second, third, fourth, and drive. The auxiliary section contains an overdrive gear known as the front drive gear. The high-range gear in this particular auxiliary section is called the rear-drive gear. There is also a low-range gear. Torque transferred through the front- rive gear produces an overdrive condition; torque transferred through the rear-drive gear produces a direct drive. The direct and overdrive gearing is used to split the high- and low-range gear ratios to provide a greater number of speed and torque selections. Table 15–1 lists the gear ratios for the eighteen forward and four reverse speeds possible with the transmission shown in Figure 15–52. It also includes the following data: main transmission gear engaged, auxiliary range (high/low) engaged, and auxiliary drive gear (direct/overdrive) engaged. As we described earlier, the splitter shift system for the direct and overdrive options is air-controlled by a button on the gearshift lever. When the transmission is in the high or low ranges, the splitter control button can be moved forward to shift the auxiliary transmission from a direct to overdrive condition. Low-range, Direct Powerflow In these gears (first, third, fifth, seventh, ninth, and #1 Reverse in Table 15–1), power flow is through the rear auxiliary drive gear (direct) and auxiliary low-range gear (Figure 15–53). A complete power flow description follows: Torque from the engine is transferred to the transmission’s input shaft. Splines on the input shaft engage internal splines in the hub of the main drive gear. Next, torque is split between the two countershaft drive gears. Torque is delivered through the twin countershafts to the mating countershaft gears of the engaged mainshaft gear. Internal clutching teeth in the hub of the engaged mainshaft gear transfer torque to the mainshaft through the appropriate sliding clutch. The mainshaft transmits torque directly to the rear auxiliary drive gear, by means of its engaged sliding clutch. The rear auxiliary drive gear splits torque between the two auxiliary section countershaft gears. Torque is delivered through both auxiliary section countershafts to the engaged reduction gear on the output shaft.

Eighteen-speed Transmissions (2 of 2)
See Table 15-1, page 453 of text book. EIGHTEEN-SPEED TRANSMISSIONS Figure 15–52 illustrates a transmission with eighteen forward speeds. The main or front gearing is a fivespeed transmission. In this particular transmission, main gears are referred to as low, first, second, third, and drive, rather than first, second, third, fourth, and drive. The auxiliary section contains an overdrive gear known as the front drive gear. The high-range gear in this particular auxiliary section is called the rear-drive gear. There is also a low-range gear. Torque transferred through the front- rive gear produces an overdrive condition; torque transferred through the rear-drive gear produces a direct drive. The direct and overdrive gearing is used to split the high- and low-range gear ratios to provide a greater number of speed and torque selections. Table 15–1 lists the gear ratios for the eighteen forward and four reverse speeds possible with the transmission shown in Figure 15–52. It also includes the following data: main transmission gear engaged, auxiliary range (high/low) engaged, and auxiliary drive gear (direct/overdrive) engaged. As we described earlier, the splitter shift system for the direct and overdrive options is air-controlled by a button on the gearshift lever. When the transmission is in the high or low ranges, the splitter control button can be moved forward to shift the auxiliary transmission from a direct to overdrive condition. Low-range, Direct Powerflow In these gears (first, third, fifth, seventh, ninth, and #1 Reverse in Table 15–1), power flow is through the rear auxiliary drive gear (direct) and auxiliary low-range gear (Figure 15–53). A complete power flow description follows: Torque from the engine is transferred to the transmission’s input shaft. Splines on the input shaft engage internal splines in the hub of the main drive gear. Next, torque is split between the two countershaft drive gears. Torque is delivered through the twin countershafts to the mating countershaft gears of the engaged mainshaft gear. Internal clutching teeth in the hub of the engaged mainshaft gear transfer torque to the mainshaft through the appropriate sliding clutch. The mainshaft transmits torque directly to the rear auxiliary drive gear, by means of its engaged sliding clutch. The rear auxiliary drive gear splits torque between the two auxiliary section countershaft gears. Torque is delivered through both auxiliary section countershafts to the engaged reduction gear on the output shaft.

Low-range, Overdrive Powerflow
The auxiliary drive gear splits torque between the two auxiliary countershafts. Torque is delivered through both countershafts to the low-range gear output shaft. The high/low synchronizer is used to lock this reduction gear to the output shaft. Torque is transferred to the output shaft through the sliding clutch of the synchronizer. Torque is delivered to the driveline as low-range overdrive. Low-range, Overdrive Powerflow In these gear selections (second, fourth, sixth, eighth, tenth, and #2 Reverse in Table 15–1), power flow is through the front auxiliary gear (overdrive) and the auxiliary low-range gear (Figure 15–54). Power flow through the main box is identical to that outlined in steps 1 through 5 under the previously described Low Range Direct description. However, the sliding clutch between the front and rear auxiliary drive gears moves forward when the driver engages the splitter control button on the shift tower. The sliding clutch locks the auxiliary front-drive gear to the range mainshaft. The power flow through the auxiliary section of the transmission is as follows: 1. The front auxiliary drive gear splits torque between the two auxiliary countershaft drive gears. 2. Torque is delivered through both countershafts to the low-range gear on the range mainshaft or output shaft. Once again, the high/low synchronizer is used to lock this lowrange or reduction gear to the output shaft. 3. Torque is transferred to the output shaft through the sliding clutch of the synchronizer. 4. Torque is delivered to the driveline as lowrange overdrive.

High-range, Direct Powerflow
In these gear selections (eleventh, thirteenth, fifteenth, seventeenth, and #3 Reverse), powerflow is through the rear auxiliary drive gear. This gear is locked to the auxiliary output shaft by the front/rear sliding clutch and the high side of the high/low range synchronizer. This locks the rear auxiliary drive gear directly to the output shaft. High-range, Direct Powerflow In these gear selections (eleventh, thirteenth, fifteenth, seventeenth, and #3 Reverse in Table 15–1), powerflow is through the rear auxiliary drive gear (Figure 15–55). This gear is locked to the auxiliary output shaft by the front/rear sliding clutch and the high side of the high/low range synchronizer. This locks the rear auxiliary drive gear directly to the output shaft. All other gears in the auxiliary section are freewheeling.

High-range/ Overdrive
In twelfth, fourteenth, sixteenth, eighteenth, and #4 Reverse, powerflow is through the front auxiliary drive gear, which is locked to the output shaft by the front/rear sliding clutch. Torque is then delivered through both auxiliary countershafts to the rear auxiliary drive gear. The rear auxiliary drive gear is locked to the output shaft by the high/low synchronizer. High-range, Overdrive Powerflow In these gear selections (twelfth, fourteenth, sixteenth, eighteenth, and #4 Reverse in Table 15–1), powerflow is through the front auxiliary drive gear, which is locked to the output shaft by the front/rear sliding clutch (Figure 15–56). This splits torque between the two auxiliary drive gears. Torque is then delivered through both auxiliary countershafts to the engaged rear auxiliary drive gear. This rear auxiliary drive gear is locked to the output shaft by the high side of the high/low range synchronizer. Power flow is through the rear gear to the synchronizer sliding clutch and out through the output shaft to the driveline.

Thirteen-speed Transmissions (1 of 4)
Similar to the eighteen-speed transmission The auxiliary section contains: A high-range gear A low-range gear An overdrive gear In some models, this overdrive gear is replaced with an underdrive gear. THIRTEEN-SPEED TRANSMISSIONS The thirteen-speed transmission illustrated in Figure 15–57 is similar to the eighteen-speed transmission described above in many ways. Once again, the main or front gearing is a five-speed transmission. The auxiliary section contains (moving from front to back) a high-range gear, a low-range gear, and an overdrive gear. In some models, this overdrive gear is replaced with an underdrive gear. As shown in Figure 15–58, the first five gear ratios (low, first, second, third, and fourth) are found with the splitter control button in the rearward (direct drive) position and the range selector in its low-range (down) position. Torque is delivered along both countershafts to the engaged low-range gear on the range mainshaft or output shaft. This creates low- range power flows through the auxiliary gearing for each of the five speeds of the main section as shown in Figure 15–57. The driver shifts to the high range by pulling up on the range selector. This action moves a sliding clutch that locks the auxiliary drive gear directly to the range mainshaft or output shaft. Torque is delivered through the range mainshaft and/or output shaft as high-range direct power flows for the next four gear ratios—fifth, sixth, seventh, and eighth (Figure 15–59). While in the high range only, the fifth, sixth, seventh, and eighth gear ratios can be “split” by moving the splitter control button on the cab shift lever to the OD or forward position. Activating the splitter shift system in this way moves a sliding clutch that locks the overdrive splitter gear in the auxiliary section to the output shaft. Torque is delivered along both auxiliary countershafts to the auxiliary overdrive gears to the output shaft overdrive gear and out through the output shaft (Figure 15–60). High-range overdrive power flows are possible for four gear ratios: overdrive fifth, overdrive sixth, overdrive seventh, and overdrive eighth. As you can see in Table 15–2, the fifth gear overdrive gear ratio falls between the fifth and sixth gear high-range direct ratios. So if the driver wished to shift progressively through all gears, the correct sequence would be: 1. High-range direct fifth gear with splitter button in rear position (disengaged). 2. Double-clutch, engaging splitter button into forward position while in neutral and shifting into high-range fifth overdrive. 3. Double-clutch, disengaging splitter button into rear position while in neutral and shifting into high-range direct sixth gear. Thirteen-speed, Underdrive. Thirteen-speed underdrive transmissions operate on the same principles except that the underdrive gear ratio for a particular gear is selected before the direct drive ratio. Underdrive ratios for a typical thirteen-speed transmission are also listed in Table 15–2.

The first five gear ratios occur with the range selector in its low-range (down) position. Torque is delivered along both countershafts to the engaged low-range gear on the range mainshaft or output shaft. This creates low- range power flows through the auxiliary gearing for each of the five speeds of the main section. THIRTEEN-SPEED TRANSMISSIONS The thirteen-speed transmission illustrated in Figure 15–57 is similar to the eighteen-speed transmission described above in many ways. Once again, the main or front gearing is a five-speed transmission. The auxiliary section contains (moving from front to back) a high-range gear, a low-range gear, and an overdrive gear. In some models, this overdrive gear is replaced with an underdrive gear. As shown in Figure 15–58, the first five gear ratios (low, first, second, third, and fourth) are found with the splitter control button in the rearward (direct drive) position and the range selector in its low-range (down) position. Torque is delivered along both countershafts to the engaged low-range gear on the range mainshaft or output shaft. This creates low- range power flows through the auxiliary gearing for each of the five speeds of the main section as shown in Figure 15–57. The driver shifts to the high range by pulling up on the range selector. This action moves a sliding clutch that locks the auxiliary drive gear directly to the range mainshaft or output shaft. Torque is delivered through the range mainshaft and/or output shaft as high-range direct power flows for the next four gear ratios—fifth, sixth, seventh, and eighth (Figure 15–59). While in the high range only, the fifth, sixth, seventh, and eighth gear ratios can be “split” by moving the splitter control button on the cab shift lever to the OD or forward position. Activating the splitter shift system in this way moves a sliding clutch that locks the overdrive splitter gear in the auxiliary section to the output shaft. Torque is delivered along both auxiliary countershafts to the auxiliary overdrive gears to the output shaft overdrive gear and out through the output shaft (Figure 15–60). High-range overdrive power flows are possible for four gear ratios: overdrive fifth, overdrive sixth, overdrive seventh, and overdrive eighth. As you can see in Table 15–2, the fifth gear overdrive gear ratio falls between the fifth and sixth gear high-range direct ratios. So if the driver wished to shift progressively through all gears, the correct sequence would be: 1. High-range direct fifth gear with splitter button in rear position (disengaged). 2. Double-clutch, engaging splitter button into forward position while in neutral and shifting into high-range fifth overdrive. 3. Double-clutch, disengaging splitter button into rear position while in neutral and shifting into high-range direct sixth gear. Thirteen-speed, Underdrive. Thirteen-speed underdrive transmissions operate on the same principles except that the underdrive gear ratio for a particular gear is selected before the direct drive ratio. Underdrive ratios for a typical thirteen-speed transmission are also listed in Table 15–2.

The driver shifts to the high range by pulling up on the range selector. This action moves a sliding clutch that locks the auxiliary drive gear directly to the range mainshaft or output shaft. Torque is delivered through the range mainshaft and/or output shaft as high-range direct power flows for the next four gear ratios—fifth, sixth, seventh, and eighth. THIRTEEN-SPEED TRANSMISSIONS The thirteen-speed transmission illustrated in Figure 15–57 is similar to the eighteen-speed transmission described above in many ways. Once again, the main or front gearing is a five-speed transmission. The auxiliary section contains (moving from front to back) a high-range gear, a low-range gear, and an overdrive gear. In some models, this overdrive gear is replaced with an underdrive gear. As shown in Figure 15–58, the first five gear ratios (low, first, second, third, and fourth) are found with the splitter control button in the rearward (direct drive) position and the range selector in its low-range (down) position. Torque is delivered along both countershafts to the engaged low-range gear on the range mainshaft or output shaft. This creates low- range power flows through the auxiliary gearing for each of the five speeds of the main section as shown in Figure 15–57. The driver shifts to the high range by pulling up on the range selector. This action moves a sliding clutch that locks the auxiliary drive gear directly to the range mainshaft or output shaft. Torque is delivered through the range mainshaft and/or output shaft as high-range direct power flows for the next four gear ratios—fifth, sixth, seventh, and eighth (Figure 15–59). While in the high range only, the fifth, sixth, seventh, and eighth gear ratios can be “split” by moving the splitter control button on the cab shift lever to the OD or forward position. Activating the splitter shift system in this way moves a sliding clutch that locks the overdrive splitter gear in the auxiliary section to the output shaft. Torque is delivered along both auxiliary countershafts to the auxiliary overdrive gears to the output shaft overdrive gear and out through the output shaft (Figure 15–60). High-range overdrive power flows are possible for four gear ratios: overdrive fifth, overdrive sixth, overdrive seventh, and overdrive eighth. As you can see in Table 15–2, the fifth gear overdrive gear ratio falls between the fifth and sixth gear high-range direct ratios. So if the driver wished to shift progressively through all gears, the correct sequence would be: 1. High-range direct fifth gear with splitter button in rear position (disengaged). 2. Double-clutch, engaging splitter button into forward position while in neutral and shifting into high-range fifth overdrive. 3. Double-clutch, disengaging splitter button into rear position while in neutral and shifting into high-range direct sixth gear. Thirteen-speed, Underdrive. Thirteen-speed underdrive transmissions operate on the same principles except that the underdrive gear ratio for a particular gear is selected before the direct drive ratio. Underdrive ratios for a typical thirteen-speed transmission are also listed in Table 15–2.

While in the high range only, the gear ratios can be “split” by moving the splitter control button to OD. This moves a sliding clutch that locks the overdrive splitter gear in the auxiliary section to the output shaft. Torque is delivered along both auxiliary countershafts to the auxiliary overdrive gears to the output shaft overdrive gear and out through the output shaft. THIRTEEN-SPEED TRANSMISSIONS The thirteen-speed transmission illustrated in Figure 15–57 is similar to the eighteen-speed transmission described above in many ways. Once again, the main or front gearing is a five-speed transmission. The auxiliary section contains (moving from front to back) a high-range gear, a low-range gear, and an overdrive gear. In some models, this overdrive gear is replaced with an underdrive gear. As shown in Figure 15–58, the first five gear ratios (low, first, second, third, and fourth) are found with the splitter control button in the rearward (direct drive) position and the range selector in its low-range (down) position. Torque is delivered along both countershafts to the engaged low-range gear on the range mainshaft or output shaft. This creates low- range power flows through the auxiliary gearing for each of the five speeds of the main section as shown in Figure 15–57. The driver shifts to the high range by pulling up on the range selector. This action moves a sliding clutch that locks the auxiliary drive gear directly to the range mainshaft or output shaft. Torque is delivered through the range mainshaft and/or output shaft as high-range direct power flows for the next four gear ratios—fifth, sixth, seventh, and eighth (Figure 15–59). While in the high range only, the fifth, sixth, seventh, and eighth gear ratios can be “split” by moving the splitter control button on the cab shift lever to the OD or forward position. Activating the splitter shift system in this way moves a sliding clutch that locks the overdrive splitter gear in the auxiliary section to the output shaft. Torque is delivered along both auxiliary countershafts to the auxiliary overdrive gears to the output shaft overdrive gear and out through the output shaft (Figure 15–60). High-range overdrive power flows are possible for four gear ratios: overdrive fifth, overdrive sixth, overdrive seventh, and overdrive eighth. As you can see in Table 15–2, the fifth gear overdrive gear ratio falls between the fifth and sixth gear high-range direct ratios. So if the driver wished to shift progressively through all gears, the correct sequence would be: 1. High-range direct fifth gear with splitter button in rear position (disengaged). 2. Double-clutch, engaging splitter button into forward position while in neutral and shifting into high-range fifth overdrive. 3. Double-clutch, disengaging splitter button into rear position while in neutral and shifting into high-range direct sixth gear. Thirteen-speed, Underdrive. Thirteen-speed underdrive transmissions operate on the same principles except that the underdrive gear ratio for a particular gear is selected before the direct drive ratio. Underdrive ratios for a typical thirteen-speed transmission are also listed in Table 15–2.

Deep-reduction Transmissions (1 of 3)
The forward gear ratios are low-low, low, and first through eighth. Low-low is a special deep-reduction gear for maximum torque. It is used to produce maximum drivetrain torque for high-load, standing starts, using a deep-reduction gear in the auxiliary section. This low-low gear is engaged by activating a split shifter or dash-mounted deep-reduction valve. It can be operated in the low range only. Deep-reduction Transmissions Figure 15–61 illustrates the shift pattern for a ten speed transmission. The forward gear ratios are low-low, low, and first through eighth. Low-low is a special deep-reduction gear for maximum torque. It is used to produce maximum drivetrain torque for high-load, standing starts, using a deep-reduction gear in the auxiliary section. This low-low gear is engaged by activating a split shifter or dash-mounted deep-reduction valve. It can be operated in the low range only. Constant air from the air filter/regulator assembly is supplied to the reduction cylinder at the port on the right side of the cylinder cover. With the deep- reduction lever in the “Out” position, the valve is opened and air is supplied to the center port of the cylinder cover, moving the reduction piston forward to disengage the deep-reduction gearing. When the lever is moved to the “In” position, the valve is closed and no air is supplied to the center port. Constant air from the air filter/regulator assembly moves the reduction piston rearward to engage the reduction gearing. As shown in Figure 15–62, the powerflow is routed through both countershafts and countershaft deep reduction gears, to the output shaft deep-reduction gear, which is locked to the output shaft by the sliding clutch. In shifting from low-low to low, the driver double clutches, releasing the split shifter and moving to low range low. Low through fourth gears are low range gear ratios. The driver then range-shifts into high range for gears five through eight.

Constant air is supplied to the reduction cylinder center port. With the deep-reduction lever in the “Out” position, the valve is opened and air is used to disengage the deep-reduction gearing. When the lever is moved to the “In” position, the valve is closed and no air is supplied to the center port. Constant air from the air filter/regulator assembly then moves the piston to engage the reduction gearing. Deep-reduction Transmissions Figure 15–61 illustrates the shift pattern for a ten speed transmission. The forward gear ratios are low-low, low, and first through eighth. Low-low is a special deep-reduction gear for maximum torque. It is used to produce maximum drivetrain torque for high-load, standing starts, using a deep-reduction gear in the auxiliary section. This low-low gear is engaged by activating a split shifter or dash-mounted deep-reduction valve. It can be operated in the low range only. Constant air from the air filter/regulator assembly is supplied to the reduction cylinder at the port on the right side of the cylinder cover. With the deep- reduction lever in the “Out” position, the valve is opened and air is supplied to the center port of the cylinder cover, moving the reduction piston forward to disengage the deep-reduction gearing. When the lever is moved to the “In” position, the valve is closed and no air is supplied to the center port. Constant air from the air filter/regulator assembly moves the reduction piston rearward to engage the reduction gearing. As shown in Figure 15–62, the powerflow is routed through both countershafts and countershaft deep reduction gears, to the output shaft deep-reduction gear, which is locked to the output shaft by the sliding clutch. In shifting from low-low to low, the driver double clutches, releasing the split shifter and moving to low range low. Low through fourth gears are low range gear ratios. The driver then range-shifts into high range for gears five through eight.

Powerflow is routed through both countershafts and countershaft deep-reduction gears, to the output shaft deep-reduction gear, which is locked to the output shaft by the sliding clutch. In shifting from low-low to low, the driver double clutches, releasing the split shifter and moving to low range low. Low through fourth gears are low-range gear ratios. The driver then range-shifts into high range for gears five through eight. Deep-reduction Transmissions Figure 15–61 illustrates the shift pattern for a ten speed transmission. The forward gear ratios are low-low, low, and first through eighth. Low-low is a special deep-reduction gear for maximum torque. It is used to produce maximum drivetrain torque for high-load, standing starts, using a deep-reduction gear in the auxiliary section. This low-low gear is engaged by activating a split shifter or dash-mounted deep-reduction valve. It can be operated in the low range only. Constant air from the air filter/regulator assembly is supplied to the reduction cylinder at the port on the right side of the cylinder cover. With the deep- reduction lever in the “Out” position, the valve is opened and air is supplied to the center port of the cylinder cover, moving the reduction piston forward to disengage the deep-reduction gearing. When the lever is moved to the “In” position, the valve is closed and no air is supplied to the center port. Constant air from the air filter/regulator assembly moves the reduction piston rearward to engage the reduction gearing. As shown in Figure 15–62, the powerflow is routed through both countershafts and countershaft deep reduction gears, to the output shaft deep-reduction gear, which is locked to the output shaft by the sliding clutch. In shifting from low-low to low, the driver double clutches, releasing the split shifter and moving to low range low. Low through fourth gears are low range gear ratios. The driver then range-shifts into high range for gears five through eight.

Transfer Cases (1 of 6) A transfer case is an additional and separate gearbox located between the main transmission and the vehicle drive axles. It functions to distribute torque from the transmission to the front and rear drive axles. Although not commonly used in trucks intended primarily for highway use, transfer cases are required when axle(s) in front of the transmission are driven. TRANSFER CASES A transfer case is an additional and separate gearbox located between the main transmission and the vehicle drive axles. It functions to distribute torque from the transmission to front and rear drive axles. Although not commonly used in trucks intended primarily for highway use, transfer cases are required when axle(s) in front of the transmission are driven. The term all-wheel drive (AWD) in heavy-duty trucks usually refers to a chassis with a front drive axle in addition to rear tandem drive axles. Vocational trucks use these three-axle drive configurations that are essential in some on/off and off-highway applications. Figure 15–63 shows a typical AWD configuration. Transfer cases can transfer drive torque directly using a 1:1 gear ratio or can be used to provide low-gear reduction ratios additional to those in the transmission. The drop box design of a transfer case housing permits its front drive shaft output to clear the underside of the main transmission (Figure 15–64). Most transfer cases are available with power takeoff (PTO) capability and front axle declutch. The front axle declutch is used to option-drive to the front axle when negotiating steep grades or slippery or rough terrain. Both the PTO and front axle drive declutch are driver engaged by dedicated shift levers.

Transfer Cases (2 of 6) The term all-wheel drive (AWD) in heavy-duty trucks usually refers to a chassis with a front drive axle in addition to rear tandem drive axles. Vocational trucks use these three-axle drive configurations that are essential in some on/off and off-highway applications. TRANSFER CASES A transfer case is an additional and separate gearbox located between the main transmission and the vehicle drive axles. It functions to distribute torque from the transmission to front and rear drive axles. Although not commonly used in trucks intended primarily for highway use, transfer cases are required when axle(s) in front of the transmission are driven. The term all-wheel drive (AWD) in heavy-duty trucks usually refers to a chassis with a front drive axle in addition to rear tandem drive axles. Vocational trucks use these three-axle drive configurations that are essential in some on/off and off-highway applications. Figure 15–63 shows a typical AWD configuration. Transfer cases can transfer drive torque directly using a 1:1 gear ratio or can be used to provide low-gear reduction ratios additional to those in the transmission. The drop box design of a transfer case housing permits its front drive shaft output to clear the underside of the main transmission (Figure 15–64). Most transfer cases are available with power takeoff (PTO) capability and front axle declutch. The front axle declutch is used to option-drive to the front axle when negotiating steep grades or slippery or rough terrain. Both the PTO and front axle drive declutch are driver engaged by dedicated shift levers.

Transfer Cases (3 of 6) Transfer cases can transfer drive torque directly using a 1:1 gear ratio or can be used to provide low-gear reduction ratios additional to those in the transmission. The drop box design of a transfer case housing permits its front drive shaft output to clear the underside of the main transmission. Most transfer cases are available with power takeoff (PTO) capability and front axle declutch. TRANSFER CASES A transfer case is an additional and separate gearbox located between the main transmission and the vehicle drive axles. It functions to distribute torque from the transmission to front and rear drive axles. Although not commonly used in trucks intended primarily for highway use, transfer cases are required when axle(s) in front of the transmission are driven. The term all-wheel drive (AWD) in heavy-duty trucks usually refers to a chassis with a front drive axle in addition to rear tandem drive axles. Vocational trucks use these three-axle drive configurations that are essential in some on/off and off-highway applications. Figure 15–63 shows a typical AWD configuration. Transfer cases can transfer drive torque directly using a 1:1 gear ratio or can be used to provide low-gear reduction ratios additional to those in the transmission. The drop box design of a transfer case housing permits its front drive shaft output to clear the underside of the main transmission (Figure 15–64). Most transfer cases are available with power takeoff (PTO) capability and front axle declutch. The front axle declutch is used to option-drive to the front axle when negotiating steep grades or slippery or rough terrain. Both the PTO and front axle drive declutch are driver engaged by dedicated shift levers.

Transfer Cases (4 of 6) The front axle declutch is used to option-drive to the front axle when negotiating steep grades or slippery or rough terrain. Both the PTO and front axle drive declutch are driver-engaged by dedicated shift levers. In addition, a transfer case might be equipped with an optional parking brake and a speedometer drive gear that can be installed on the idler assembly. TRANSFER CASES A transfer case is an additional and separate gearbox located between the main transmission and the vehicle drive axles. It functions to distribute torque from the transmission to front and rear drive axles. Although not commonly used in trucks intended primarily for highway use, transfer cases are required when axle(s) in front of the transmission are driven. The term all-wheel drive (AWD) in heavy-duty trucks usually refers to a chassis with a front drive axle in addition to rear tandem drive axles. Vocational trucks use these three-axle drive configurations that are essential in some on/off and off-highway applications. Figure 15–63 shows a typical AWD configuration. Transfer cases can transfer drive torque directly using a 1:1 gear ratio or can be used to provide low-gear reduction ratios additional to those in the transmission. The drop box design of a transfer case housing permits its front drive shaft output to clear the underside of the main transmission (Figure 15–64). Most transfer cases are available with power takeoff (PTO) capability and front axle declutch. The front axle declutch is used to option-drive to the front axle when negotiating steep grades or slippery or rough terrain. Both the PTO and front axle drive declutch are driver engaged by dedicated shift levers. In addition, a transfer case might be equipped with an optional parking brake and a speedometer drive gear that can be installed on the idler assembly. Most transfer cases use the countershaft design and the gearing is of the constant-mesh, helical-cut type. The countershafts are usually mounted in ball or taper roller bearings. The moving components of a transfer case are splash-lubricated by oil in the housing during operation. Some transfer cases use an auxiliary oil pump externally mounted to the transfer case. Transfer cases may also be equipped with a driver controlled, air-actuated differential lockout to improve traction under extreme conditions. A conventional transfer case is shown in Figure 15–65. This unit is a two-speed, three-shaft design. It is commonly adapted to incorporate a PTO and front- xle declutch capability. A cutaway view of a fully equipped, three-shaft transfer case is shown in Figure 15–66. Note the means used to effect range shifts and the PTO output. Another type of transfer case is the cloverleaf four shaft design as shown in Figure 15–67. This two speed, four-shaft design can be also be adapted to incorporate a PTO and a mechanical-type auxiliary brake. Sectional views of a cloverleaf-type transfer case are shown in Figure 15–68. As can be seen in the sectional views, most transfer cases use simple gear designs; most have access panels to allow the technician to inspect and service the unit. The torque range window of transfer cases varies with application but you should note that this is spec’d to the transmission, not the engine, output torque range.

Transfer Cases (5 of 6) Most transfer cases use a countershaft with helical-cut gears. The countershafts are usually mounted in ball or taper roller bearings. Some transfer cases use an auxiliary oil pump externally mounted to the transfer case. Transfer cases may also be equipped with a driver-controlled, air-actuated differential lockout to improve traction under extreme conditions. TRANSFER CASES A transfer case is an additional and separate gearbox located between the main transmission and the vehicle drive axles. It functions to distribute torque from the transmission to front and rear drive axles. Although not commonly used in trucks intended primarily for highway use, transfer cases are required when axle(s) in front of the transmission are driven. The term all-wheel drive (AWD) in heavy-duty trucks usually refers to a chassis with a front drive axle in addition to rear tandem drive axles. Vocational trucks use these three-axle drive configurations that are essential in some on/off and off-highway applications. Figure 15–63 shows a typical AWD configuration. Transfer cases can transfer drive torque directly using a 1:1 gear ratio or can be used to provide low-gear reduction ratios additional to those in the transmission. The drop box design of a transfer case housing permits its front drive shaft output to clear the underside of the main transmission (Figure 15–64). Most transfer cases are available with power takeoff (PTO) capability and front axle declutch. The front axle declutch is used to option-drive to the front axle when negotiating steep grades or slippery or rough terrain. Both the PTO and front axle drive declutch are driver engaged by dedicated shift levers. In addition, a transfer case might be equipped with an optional parking brake and a speedometer drive gear that can be installed on the idler assembly. Most transfer cases use the countershaft design and the gearing is of the constant-mesh, helical-cut type. The countershafts are usually mounted in ball or taper roller bearings. The moving components of a transfer case are splash-lubricated by oil in the housing during operation. Some transfer cases use an auxiliary oil pump externally mounted to the transfer case. Transfer cases may also be equipped with a driver controlled, air-actuated differential lockout to improve traction under extreme conditions. A conventional transfer case is shown in Figure 15–65. This unit is a two-speed, three-shaft design. It is commonly adapted to incorporate a PTO and front- xle declutch capability. A cutaway view of a fully equipped, three-shaft transfer case is shown in Figure 15–66. Note the means used to effect range shifts and the PTO output. Another type of transfer case is the cloverleaf four shaft design as shown in Figure 15–67. This two speed, four-shaft design can be also be adapted to incorporate a PTO and a mechanical-type auxiliary brake. Sectional views of a cloverleaf-type transfer case are shown in Figure 15–68. As can be seen in the sectional views, most transfer cases use simple gear designs; most have access panels to allow the technician to inspect and service the unit. The torque range window of transfer cases varies with application but you should note that this is spec’d to the transmission, not the engine, output torque range.

Transfer Cases (6 of 6) Another type of transfer case is the cloverleaf four shaft design. This two-speed, four-shaft design can also be adapted to incorporate a PTO and a mechanical-type auxiliary brake. TRANSFER CASES A transfer case is an additional and separate gearbox located between the main transmission and the vehicle drive axles. It functions to distribute torque from the transmission to front and rear drive axles. Although not commonly used in trucks intended primarily for highway use, transfer cases are required when axle(s) in front of the transmission are driven. The term all-wheel drive (AWD) in heavy-duty trucks usually refers to a chassis with a front drive axle in addition to rear tandem drive axles. Vocational trucks use these three-axle drive configurations that are essential in some on/off and off-highway applications. Figure 15–63 shows a typical AWD configuration. Transfer cases can transfer drive torque directly using a 1:1 gear ratio or can be used to provide low-gear reduction ratios additional to those in the transmission. The drop box design of a transfer case housing permits its front drive shaft output to clear the underside of the main transmission (Figure 15–64). Most transfer cases are available with power takeoff (PTO) capability and front axle declutch. The front axle declutch is used to option-drive to the front axle when negotiating steep grades or slippery or rough terrain. Both the PTO and front axle drive declutch are driver engaged by dedicated shift levers. In addition, a transfer case might be equipped with an optional parking brake and a speedometer drive gear that can be installed on the idler assembly. Most transfer cases use the countershaft design and the gearing is of the constant-mesh, helical-cut type. The countershafts are usually mounted in ball or taper roller bearings. The moving components of a transfer case are splash-lubricated by oil in the housing during operation. Some transfer cases use an auxiliary oil pump externally mounted to the transfer case. Transfer cases may also be equipped with a driver controlled, air-actuated differential lockout to improve traction under extreme conditions. A conventional transfer case is shown in Figure 15–65. This unit is a two-speed, three-shaft design. It is commonly adapted to incorporate a PTO and front- xle declutch capability. A cutaway view of a fully equipped, three-shaft transfer case is shown in Figure 15–66. Note the means used to effect range shifts and the PTO output. Another type of transfer case is the cloverleaf four shaft design as shown in Figure 15–67. This two speed, four-shaft design can be also be adapted to incorporate a PTO and a mechanical-type auxiliary brake. Sectional views of a cloverleaf-type transfer case are shown in Figure 15–68. As can be seen in the sectional views, most transfer cases use simple gear designs; most have access panels to allow the technician to inspect and service the unit. The torque range window of transfer cases varies with application but you should note that this is spec’d to the transmission, not the engine, output torque range.

Power Take-offs (1 of 5) A variety of accessories on heavy-duty trucks require an auxiliary drive. Auxiliary drive can be sourced directly from the engine or by means of the transmission or transfer case. Auxiliary drive systems on trucks are usually known as PTOs. The PTO is simply a means of using the chassis engine to power accessories, eliminating the need for an additional auxiliary engine. POWER TAKEOFF UNITS A variety of accessories on heavy-duty trucks require an auxiliary drive. Auxiliary drive can be sourced directly from the engine or by means of the transmission or transfer case. Auxiliary drive systems on trucks are usually known as PTOs, and that is the term we will use in this text. When a PTO is coupled to the transmission or transfer case it is an assembly such as the one shown in Figure 15–69, and a typical installation is shown in Figure 15–70. The PTO is simply a means of using the chassis engine to power accessories, eliminating the need for an additional auxiliary engine. There are six basic types of PTOs classified by their installation location or drive source: Side mount Split shaft Top mount Countershaft Forward crankshaft driven Rear crankshaft or flywheel driven A side-mount PTO is bolted to the side of the main transmission and is the most common type found on trucks. A split-shaft PTO transmits torque from the chassis drive shaft and is located behind the transmission; split-shaft PTOs require special mounting to the chassis frame. A top-mount PTO is usually found mounted to the top of an auxiliary transmission. A countershaft PTO is mounted behind the transmissions and when used replaces the bearing cap located at the rear of one countershaft on a twin countershaft transmission. The forward crankshaft–driven PTO is driven by gearing at the front of the engine crankshaft. It is used in applications that require auxiliary power while the truck is in motion, such as cement mixers. Clutchtype crankshaft-driven PTOs are used so that engagement/ disengagement can take place while the engine is running. A flywheel PTO is sandwiched between the bell housing and the transmission. Like the forward crankshaft–driven PTO, a flywheel PTO permits continuous operation. The objective of a PTO is to provide driving torque to auxiliary equipment such as pumps and compressors. The driven equipment can be mounted either directly to the PTO or indirectly using a small drive shaft. The PTO input gear is placed in constant mesh with a gear in the truck transmission (Figure 15–71). Also, refer to Figure 15–36 and Figure 15–52 earlier in this chapter. You can see that the PTO couples into these transmissions by means of a dedicated PTO gear on the transmission countershaft. Any rotation of the PTO countershaft gear drives the PTO input gear. The on/off capability required by a PTO is provided within the PTO assembly. Gears in most PTO units can be either spur or helical. Establishing the correct mesh between the PTO drive gear and its partner in the transmission is critical: Too much or too little backlash can produce problems. Gear ratio is also critical in PTO operation. Gear ratio must be set to the torque capacity and operating speed required of the driven equipment. An exploded view of a typical PTO unit is shown in Figure 15–72. As previously discussed, some PTOs function whenever the vehicle engine is running. These can operate at a fixed ratio of engine speed, while others vary depending on which gear the transmission is in. Other PTOs are designed to work only when the transmission has been shifted to the neutral position. All transmission mounted PTOs are clutch- ependent in that they only transmit torque when the vehicle clutch is engaged. Flywheel and forward crankshaft– driven PTOs operate independently of vehicle clutch engagement, so they are used in applications where continuous auxiliary power is required; a mobile cement mixer cylinder would be an example. Several types of shift mechanisms are used to connect the power takeoff with operator controls. Cable, lever, air, electric-over-air, and electric are options used on trucks. Because the PTO requirements on most highway trucks are modest—usually a hydraulic pump or compressor—the cable-type control system is most commonly used. Some current units are equipped to use electronic-over-electric PTO controls. Most PTOs feature simple designs and rugged construction. Care should be taken to properly mount a PTO. Setting backlash to specification is critical; this operation is performed by setting the gasket thickness at the PTO mounting flange. Contaminated transmission oil can damage a PTO so regular maintenance is important. PTO Management The load a PTO subjects the engine to tends to be light because auxiliary equipment, such as pumps and compressors, only requires a fraction of the engine horsepower. PTO hydraulic pumps are often used to pump a liquid load from a tanker and PTO compressors are used to blow light solids from sealed bulk hoppers. Most current truck engines have at least two electronically managed PTO operating modes. One of these is always isochronous, meaning that the engine can be set to run at a continuous rpm, regardless of actual load. Most PTO-driven auxiliary equipment is designed to be run at a set rpm for optimum efficiency; check with the OEM literature before operating.

Power Take-offs (2 of 5) There are six basic types of PTOs classified by their installation location or drive source: Side-mount PTO is bolted to the side of the main transmission and is the most common type found on trucks. A split-shaft PTO transmits torque from the chassis drive shaft and is located behind the transmission; split-shaft PTOs require special mounting to the chassis frame. POWER TAKEOFF UNITS A variety of accessories on heavy-duty trucks require an auxiliary drive. Auxiliary drive can be sourced directly from the engine or by means of the transmission or transfer case. Auxiliary drive systems on trucks are usually known as PTOs, and that is the term we will use in this text. When a PTO is coupled to the transmission or transfer case it is an assembly such as the one shown in Figure 15–69, and a typical installation is shown in Figure 15–70. The PTO is simply a means of using the chassis engine to power accessories, eliminating the need for an additional auxiliary engine. There are six basic types of PTOs classified by their installation location or drive source: Side mount Split shaft Top mount Countershaft Forward crankshaft driven Rear crankshaft or flywheel driven A side-mount PTO is bolted to the side of the main transmission and is the most common type found on trucks. A split-shaft PTO transmits torque from the chassis drive shaft and is located behind the transmission; split-shaft PTOs require special mounting to the chassis frame. A top-mount PTO is usually found mounted to the top of an auxiliary transmission. A countershaft PTO is mounted behind the transmissions and when used replaces the bearing cap located at the rear of one countershaft on a twin countershaft transmission. The forward crankshaft–driven PTO is driven by gearing at the front of the engine crankshaft. It is used in applications that require auxiliary power while the truck is in motion, such as cement mixers. Clutchtype crankshaft-driven PTOs are used so that engagement/ disengagement can take place while the engine is running. A flywheel PTO is sandwiched between the bell housing and the transmission. Like the forward crankshaft–driven PTO, a flywheel PTO permits continuous operation. The objective of a PTO is to provide driving torque to auxiliary equipment such as pumps and compressors. The driven equipment can be mounted either directly to the PTO or indirectly using a small drive shaft. The PTO input gear is placed in constant mesh with a gear in the truck transmission (Figure 15–71). Also, refer to Figure 15–36 and Figure 15–52 earlier in this chapter. You can see that the PTO couples into these transmissions by means of a dedicated PTO gear on the transmission countershaft. Any rotation of the PTO countershaft gear drives the PTO input gear. The on/off capability required by a PTO is provided within the PTO assembly. Gears in most PTO units can be either spur or helical. Establishing the correct mesh between the PTO drive gear and its partner in the transmission is critical: Too much or too little backlash can produce problems. Gear ratio is also critical in PTO operation. Gear ratio must be set to the torque capacity and operating speed required of the driven equipment. An exploded view of a typical PTO unit is shown in Figure 15–72. As previously discussed, some PTOs function whenever the vehicle engine is running. These can operate at a fixed ratio of engine speed, while others vary depending on which gear the transmission is in. Other PTOs are designed to work only when the transmission has been shifted to the neutral position. All transmission mounted PTOs are clutch- ependent in that they only transmit torque when the vehicle clutch is engaged. Flywheel and forward crankshaft– driven PTOs operate independently of vehicle clutch engagement, so they are used in applications where continuous auxiliary power is required; a mobile cement mixer cylinder would be an example. Several types of shift mechanisms are used to connect the power takeoff with operator controls. Cable, lever, air, electric-over-air, and electric are options used on trucks. Because the PTO requirements on most highway trucks are modest—usually a hydraulic pump or compressor—the cable-type control system is most commonly used. Some current units are equipped to use electronic-over-electric PTO controls. Most PTOs feature simple designs and rugged construction. Care should be taken to properly mount a PTO. Setting backlash to specification is critical; this operation is performed by setting the gasket thickness at the PTO mounting flange. Contaminated transmission oil can damage a PTO so regular maintenance is important. PTO Management The load a PTO subjects the engine to tends to be light because auxiliary equipment, such as pumps and compressors, only requires a fraction of the engine horsepower. PTO hydraulic pumps are often used to pump a liquid load from a tanker and PTO compressors are used to blow light solids from sealed bulk hoppers. Most current truck engines have at least two electronically managed PTO operating modes. One of these is always isochronous, meaning that the engine can be set to run at a continuous rpm, regardless of actual load. Most PTO-driven auxiliary equipment is designed to be run at a set rpm for optimum efficiency; check with the OEM literature before operating.

Power Take-offs (3 of 5) Clutch-type crankshaft-driven PTOs are used so that engagement/ disengagement can take place while the engine is running. A flywheel PTO is sandwiched between the bell housing and the transmission. Rear crankshaft or flywheel-driven: Like the forward crankshaft–driven PTO, a flywheel PTO permits continuous operation. POWER TAKEOFF UNITS A variety of accessories on heavy-duty trucks require an auxiliary drive. Auxiliary drive can be sourced directly from the engine or by means of the transmission or transfer case. Auxiliary drive systems on trucks are usually known as PTOs, and that is the term we will use in this text. When a PTO is coupled to the transmission or transfer case it is an assembly such as the one shown in Figure 15–69, and a typical installation is shown in Figure 15–70. The PTO is simply a means of using the chassis engine to power accessories, eliminating the need for an additional auxiliary engine. There are six basic types of PTOs classified by their installation location or drive source: Side mount Split shaft Top mount Countershaft Forward crankshaft driven Rear crankshaft or flywheel driven A side-mount PTO is bolted to the side of the main transmission and is the most common type found on trucks. A split-shaft PTO transmits torque from the chassis drive shaft and is located behind the transmission; split-shaft PTOs require special mounting to the chassis frame. A top-mount PTO is usually found mounted to the top of an auxiliary transmission. A countershaft PTO is mounted behind the transmissions and when used replaces the bearing cap located at the rear of one countershaft on a twin countershaft transmission. The forward crankshaft–driven PTO is driven by gearing at the front of the engine crankshaft. It is used in applications that require auxiliary power while the truck is in motion, such as cement mixers. Clutch-type crankshaft-driven PTOs are used so that engagement/ disengagement can take place while the engine is running. A flywheel PTO is sandwiched between the bell housing and the transmission. Like the forward crankshaft–driven PTO, a flywheel PTO permits continuous operation. The objective of a PTO is to provide driving torque to auxiliary equipment such as pumps and compressors. The driven equipment can be mounted either directly to the PTO or indirectly using a small drive shaft. The PTO input gear is placed in constant mesh with a gear in the truck transmission (Figure 15–71). Also, refer to Figure 15–36 and Figure 15–52 earlier in this chapter. You can see that the PTO couples into these transmissions by means of a dedicated PTO gear on the transmission countershaft. Any rotation of the PTO countershaft gear drives the PTO input gear. The on/off capability required by a PTO is provided within the PTO assembly. Gears in most PTO units can be either spur or helical. Establishing the correct mesh between the PTO drive gear and its partner in the transmission is critical: Too much or too little backlash can produce problems. Gear ratio is also critical in PTO operation. Gear ratio must be set to the torque capacity and operating speed required of the driven equipment. An exploded view of a typical PTO unit is shown in Figure 15–72. As previously discussed, some PTOs function whenever the vehicle engine is running. These can operate at a fixed ratio of engine speed, while others vary depending on which gear the transmission is in. Other PTOs are designed to work only when the transmission has been shifted to the neutral position. All transmission mounted PTOs are clutch- ependent in that they only transmit torque when the vehicle clutch is engaged. Flywheel and forward crankshaft– driven PTOs operate independently of vehicle clutch engagement, so they are used in applications where continuous auxiliary power is required; a mobile cement mixer cylinder would be an example. Several types of shift mechanisms are used to connect the power takeoff with operator controls. Cable, lever, air, electric-over-air, and electric are options used on trucks. Because the PTO requirements on most highway trucks are modest—usually a hydraulic pump or compressor—the cable-type control system is most commonly used. Some current units are equipped to use electronic-over-electric PTO controls. Most PTOs feature simple designs and rugged construction. Care should be taken to properly mount a PTO. Setting backlash to specification is critical; this operation is performed by setting the gasket thickness at the PTO mounting flange. Contaminated transmission oil can damage a PTO so regular maintenance is important. PTO Management The load a PTO subjects the engine to tends to be light because auxiliary equipment, such as pumps and compressors, only requires a fraction of the engine horsepower. PTO hydraulic pumps are often used to pump a liquid load from a tanker and PTO compressors are used to blow light solids from sealed bulk hoppers. Most current truck engines have at least two electronically managed PTO operating modes. One of these is always isochronous, meaning that the engine can be set to run at a continuous rpm, regardless of actual load. Most PTO-driven auxiliary equipment is designed to be run at a set rpm for optimum efficiency; check with the OEM literature before operating.

Power Take-offs (4 of 5) The objective of a PTO is to provide driving torque to auxiliary equipment such as pumps and compressors. The driven equipment can be mounted either directly to the PTO or indirectly using a small drive shaft. The PTO input gear is placed in constant mesh with a gear in the truck transmission. POWER TAKEOFF UNITS A variety of accessories on heavy-duty trucks require an auxiliary drive. Auxiliary drive can be sourced directly from the engine or by means of the transmission or transfer case. Auxiliary drive systems on trucks are usually known as PTOs, and that is the term we will use in this text. When a PTO is coupled to the transmission or transfer case it is an assembly such as the one shown in Figure 15–69, and a typical installation is shown in Figure 15–70. The PTO is simply a means of using the chassis engine to power accessories, eliminating the need for an additional auxiliary engine. There are six basic types of PTOs classified by their installation location or drive source: Side mount Split shaft Top mount Countershaft Forward crankshaft driven Rear crankshaft or flywheel driven A side-mount PTO is bolted to the side of the main transmission and is the most common type found on trucks. A split-shaft PTO transmits torque from the chassis drive shaft and is located behind the transmission; split-shaft PTOs require special mounting to the chassis frame. A top-mount PTO is usually found mounted to the top of an auxiliary transmission. A countershaft PTO is mounted behind the transmissions and when used replaces the bearing cap located at the rear of one countershaft on a twin countershaft transmission. The forward crankshaft–driven PTO is driven by gearing at the front of the engine crankshaft. It is used in applications that require auxiliary power while the truck is in motion, such as cement mixers. Clutchtype crankshaft-driven PTOs are used so that engagement/ disengagement can take place while the engine is running. A flywheel PTO is sandwiched between the bell housing and the transmission. Like the forward crankshaft–driven PTO, a flywheel PTO permits continuous operation. The objective of a PTO is to provide driving torque to auxiliary equipment such as pumps and compressors. The driven equipment can be mounted either directly to the PTO or indirectly using a small drive shaft. The PTO input gear is placed in constant mesh with a gear in the truck transmission (Figure 15–71). Also, refer to Figure 15–36 and Figure 15–52 earlier in this chapter. You can see that the PTO couples into these transmissions by means of a dedicated PTO gear on the transmission countershaft. Any rotation of the PTO countershaft gear drives the PTO input gear. The on/off capability required by a PTO is provided within the PTO assembly. Gears in most PTO units can be either spur or helical. Establishing the correct mesh between the PTO drive gear and its partner in the transmission is critical: Too much or too little backlash can produce problems. Gear ratio is also critical in PTO operation. Gear ratio must be set to the torque capacity and operating speed required of the driven equipment. An exploded view of a typical PTO unit is shown in Figure 15–72. As previously discussed, some PTOs function whenever the vehicle engine is running. These can operate at a fixed ratio of engine speed, while others vary depending on which gear the transmission is in. Other PTOs are designed to work only when the transmission has been shifted to the neutral position. All transmission mounted PTOs are clutch- ependent in that they only transmit torque when the vehicle clutch is engaged. Flywheel and forward crankshaft– driven PTOs operate independently of vehicle clutch engagement, so they are used in applications where continuous auxiliary power is required; a mobile cement mixer cylinder would be an example. Several types of shift mechanisms are used to connect the power takeoff with operator controls. Cable, lever, air, electric-over-air, and electric are options used on trucks. Because the PTO requirements on most highway trucks are modest—usually a hydraulic pump or compressor—the cable-type control system is most commonly used. Some current units are equipped to use electronic-over-electric PTO controls. Most PTOs feature simple designs and rugged construction. Care should be taken to properly mount a PTO. Setting backlash to specification is critical; this operation is performed by setting the gasket thickness at the PTO mounting flange. Contaminated transmission oil can damage a PTO so regular maintenance is important. PTO Management The load a PTO subjects the engine to tends to be light because auxiliary equipment, such as pumps and compressors, only requires a fraction of the engine horsepower. PTO hydraulic pumps are often used to pump a liquid load from a tanker and PTO compressors are used to blow light solids from sealed bulk hoppers. Most current truck engines have at least two electronically managed PTO operating modes. One of these is always isochronous, meaning that the engine can be set to run at a continuous rpm, regardless of actual load. Most PTO-driven auxiliary equipment is designed to be run at a set rpm for optimum efficiency; check with the OEM literature before operating.

Power Take-offs (5 of 5) Establishing the correct mesh between the PTO drive gear and its partner in the transmission is critical. Too much or too little backlash can produce problems. Gear ratio is also critical in PTO operation. Gear ratio must be set to the torque capacity and operating speed required of the driven equipment. POWER TAKEOFF UNITS A variety of accessories on heavy-duty trucks require an auxiliary drive. Auxiliary drive can be sourced directly from the engine or by means of the transmission or transfer case. Auxiliary drive systems on trucks are usually known as PTOs, and that is the term we will use in this text. When a PTO is coupled to the transmission or transfer case it is an assembly such as the one shown in Figure 15–69, and a typical installation is shown in Figure 15–70. The PTO is simply a means of using the chassis engine to power accessories, eliminating the need for an additional auxiliary engine. There are six basic types of PTOs classified by their installation location or drive source: Side mount Split shaft Top mount Countershaft Forward crankshaft driven Rear crankshaft or flywheel driven A side-mount PTO is bolted to the side of the main transmission and is the most common type found on trucks. A split-shaft PTO transmits torque from the chassis drive shaft and is located behind the transmission; split-shaft PTOs require special mounting to the chassis frame. A top-mount PTO is usually found mounted to the top of an auxiliary transmission. A countershaft PTO is mounted behind the transmissions and when used replaces the bearing cap located at the rear of one countershaft on a twin countershaft transmission. The forward crankshaft–driven PTO is driven by gearing at the front of the engine crankshaft. It is used in applications that require auxiliary power while the truck is in motion, such as cement mixers. Clutchtype crankshaft-driven PTOs are used so that engagement/ disengagement can take place while the engine is running. A flywheel PTO is sandwiched between the bell housing and the transmission. Like the forward crankshaft–driven PTO, a flywheel PTO permits continuous operation. The objective of a PTO is to provide driving torque to auxiliary equipment such as pumps and compressors. The driven equipment can be mounted either directly to the PTO or indirectly using a small drive shaft. The PTO input gear is placed in constant mesh with a gear in the truck transmission (Figure 15–71). Also, refer to Figure 15–36 and Figure 15–52 earlier in this chapter. You can see that the PTO couples into these transmissions by means of a dedicated PTO gear on the transmission countershaft. Any rotation of the PTO countershaft gear drives the PTO input gear. The on/off capability required by a PTO is provided within the PTO assembly. Gears in most PTO units can be either spur or helical. Establishing the correct mesh between the PTO drive gear and its partner in the transmission is critical: Too much or too little backlash can produce problems. Gear ratio is also critical in PTO operation. Gear ratio must be set to the torque capacity and operating speed required of the driven equipment. An exploded view of a typical PTO unit is shown in Figure 15–72. As previously discussed, some PTOs function whenever the vehicle engine is running. These can operate at a fixed ratio of engine speed, while others vary depending on which gear the transmission is in. Other PTOs are designed to work only when the transmission has been shifted to the neutral position. All transmission mounted PTOs are clutch- ependent in that they only transmit torque when the vehicle clutch is engaged. Flywheel and forward crankshaft– driven PTOs operate independently of vehicle clutch engagement, so they are used in applications where continuous auxiliary power is required; a mobile cement mixer cylinder would be an example. Several types of shift mechanisms are used to connect the power takeoff with operator controls. Cable, lever, air, electric-over-air, and electric are options used on trucks. Because the PTO requirements on most highway trucks are modest—usually a hydraulic pump or compressor—the cable-type control system is most commonly used. Some current units are equipped to use electronic-over-electric PTO controls. Most PTOs feature simple designs and rugged construction. Care should be taken to properly mount a PTO. Setting backlash to specification is critical; this operation is performed by setting the gasket thickness at the PTO mounting flange. Contaminated transmission oil can damage a PTO so regular maintenance is important. PTO Management The load a PTO subjects the engine to tends to be light because auxiliary equipment, such as pumps and compressors, only requires a fraction of the engine horsepower. PTO hydraulic pumps are often used to pump a liquid load from a tanker and PTO compressors are used to blow light solids from sealed bulk hoppers. Most current truck engines have at least two electronically managed PTO operating modes. One of these is always isochronous, meaning that the engine can be set to run at a continuous rpm, regardless of actual load. Most PTO-driven auxiliary equipment is designed to be run at a set rpm for optimum efficiency; check with the OEM literature before operating.

Summary (1 of 9) Engine torque is transferred through the clutch to the input shaft of the transmission, which drives the gears in the transmission. The transmission manages the drivetrain. It is the driver’s means of managing drivetrain torque and speed ratios to suit chassis load and road conditions. A transmission enables the engine to function over a broad range of operating requirements that vary from a fully loaded standing start to cruising at highway speeds. Engine torque is transferred through the clutch to the input shaft of the transmission, which drives the gears in the transmission. The transmission manages the drivetrain. It is the driver’s means of managing drivetrain torque and speed ratios to suit chassis load and road conditions. A transmission enables the engine to function over a broad range of operating requirements that vary from a fully loaded standing start to cruising at highway speeds. Light-duty truck transmissions have a limited number of gear ratios and a single set of gears called main gearing, contained in a single housing. Most heavy-duty truck transmissions consist of two distinct sets of gearing: the main or front gearing, and the auxiliary gearing located directly on the rear of the main gearing. Auxiliary gearing compounds the available ratios in a transmission. Most heavy-duty trucks use at least one compound, some two compounds. Gear pitch refers to the number of teeth per unit of pitch diameter. The three stages of contact through which the teeth of two gears pass while in operation are coming-into-mesh, full-mesh, and coming-out-of mesh. The relationship of input to output speeds is expressed as gear ratio. Torque increase from a driving gear to a driven gear is directly proportional to speed decrease. So, to increase output torque there is a resultant decrease in output speed. And vice versa. The major types of gear tooth design used in modern transmissions and differentials are spur gears and helical gears. A heavy-duty standard transmission consists of a mainshaft and one, two, or three countershafts. Standard transmissions can be generally classified by how they are shifted. Sliding gear, collar shift, and synchronized shift mechanisms are used to effect shifts in standard transmissions. Synchronizers have two primary functions. First, they bring two components rotating at different speeds to a single, synchronized speed; and second, they lock these components together. Block or cone and pin synchronizers are the most common in heavy-duty transmissions. Most standard truck transmissions use mechanically shifted main sections: either a direct-actuated, shift tower assembly, or, in the case of COE trucks, a remote-actuated shift tower. Most current compounded transmissions use air controls to effect shifts in the auxiliary section, though some older trucks used gear levers for both main and auxiliary section shifts. An air-actuated gearshift system consists of an air filter and regulator, slave valve, master control valve, range cylinder, and connecting air lines. Auxiliary section gearing can be optioned to include a third gear in addition to the high- and low-range gears. This third gear is engaged or disengaged by a splitter shift system air activated by a button on the shift lever. A transfer case is an additional gear box located between the main transmission and the rear axle. Its function is to divide torque from the transmission to front and rear drive axles and, in addition, to option driving force to the front axle. The accessory drive requirements on trucks are met by using power takeoff (PTO) units. Hydraulic pumps for pumping loads off trailers and compressors for blowing loads off sealed bulk hoppers would be two examples of PTO-driven equipment. The six types of PTOs, classified by their installation, are side mount, split shaft, top mount, countershaft, crankshaft driven, and flywheel.

Summary (2 of 9) Light-duty truck transmissions have a limited number of gear ratios and a single set of gears called main gearing, contained in a single housing. Most heavy-duty truck transmissions consist of two distinct sets of gearing: the main or front gearing, and the auxiliary gearing located directly on the rear of the main gearing. Auxiliary gearing compounds the available ratios in a transmission. Most heavy-duty trucks use at least one compound; some use two compounds

Summary (3 of 9) Gear pitch refers to the number of teeth per unit of pitch diameter. The three stages of contact through which the teeth of two gears pass while in operation are coming-into-mesh, full-mesh, and coming-out-of mesh. The relationship of input to output speeds is expressed as gear ratio. Engine torque is transferred through the clutch to the input shaft of the transmission, which drives the gears in the transmission. The transmission manages the drivetrain. It is the driver’s means of managing drivetrain torque and speed ratios to suit chassis load and road conditions. A transmission enables the engine to function over a broad range of operating requirements that vary from a fully loaded standing start to cruising at highway speeds. Light-duty truck transmissions have a limited number of gear ratios and a single set of gears called main gearing, contained in a single housing. Most heavy-duty truck transmissions consist of two distinct sets of gearing: the main or front gearing, and the auxiliary gearing located directly on the rear of the main gearing. Auxiliary gearing compounds the available ratios in a transmission. Most heavy-duty trucks use at least one compound, some two compounds. Gear pitch refers to the number of teeth per unit of pitch diameter. The three stages of contact through which the teeth of two gears pass while in operation are coming-into-mesh, full-mesh, and coming-out-of mesh. The relationship of input to output speeds is expressed as gear ratio. Torque increase from a driving gear to a driven gear is directly proportional to speed decrease. So, to increase output torque there is a resultant decrease in output speed. And vice versa. The major types of gear tooth design used in modern transmissions and differentials are spur gears and helical gears. A heavy-duty standard transmission consists of a mainshaft and one, two, or three countershafts. Standard transmissions can be generally classified by how they are shifted. Sliding gear, collar shift, and synchronized shift mechanisms are used to effect shifts in standard transmissions. Synchronizers have two primary functions. First, they bring two components rotating at different speeds to a single, synchronized speed; and second, they lock these components together. Block or cone and pin synchronizers are the most common in heavy-duty transmissions. Most standard truck transmissions use mechanically shifted main sections: either a direct-actuated, shift tower assembly, or, in the case of COE trucks, a remote-actuated shift tower. Most current compounded transmissions use air controls to effect shifts in the auxiliary section, though some older trucks used gear levers for both main and auxiliary section shifts. An air-actuated gearshift system consists of an air filter and regulator, slave valve, master control valve, range cylinder, and connecting air lines. Auxiliary section gearing can be optioned to include a third gear in addition to the high- and low-range gears. This third gear is engaged or disengaged by a splitter shift system air activated by a button on the shift lever. A transfer case is an additional gear box located between the main transmission and the rear axle. Its function is to divide torque from the transmission to front and rear drive axles and, in addition, to option driving force to the front axle. The accessory drive requirements on trucks are met by using power takeoff (PTO) units. Hydraulic pumps for pumping loads off trailers and compressors for blowing loads off sealed bulk hoppers would be two examples of PTO-driven equipment. The six types of PTOs, classified by their installation, are side mount, split shaft, top mount, countershaft, crankshaft driven, and flywheel.

Summary (4 of 9) Torque increase from a driving gear to a driven gear is directly proportional to speed decrease. So, to increase output torque, there is a resultant decrease in output speed, and vice versa. The major types of gear tooth design used in modern transmissions and differentials are spur gears and helical gears.

Summary (5 of 9) A heavy-duty standard transmission consists of a mainshaft and one, two, or three countershafts. Standard transmissions can be generally classified by how they are shifted. Sliding gear, collar shift, and synchronized shift mechanisms are used to effect shifts in standard transmissions. Engine torque is transferred through the clutch to the input shaft of the transmission, which drives the gears in the transmission. The transmission manages the drivetrain. It is the driver’s means of managing drivetrain torque and speed ratios to suit chassis load and road conditions. A transmission enables the engine to function over a broad range of operating requirements that vary from a fully loaded standing start to cruising at highway speeds. Light-duty truck transmissions have a limited number of gear ratios and a single set of gears called main gearing, contained in a single housing. Most heavy-duty truck transmissions consist of two distinct sets of gearing: the main or front gearing, and the auxiliary gearing located directly on the rear of the main gearing. Auxiliary gearing compounds the available ratios in a transmission. Most heavy-duty trucks use at least one compound, some two compounds. Gear pitch refers to the number of teeth per unit of pitch diameter. The three stages of contact through which the teeth of two gears pass while in operation are coming-into-mesh, full-mesh, and coming-out-of mesh. The relationship of input to output speeds is expressed as gear ratio. Torque increase from a driving gear to a driven gear is directly proportional to speed decrease. So, to increase output torque there is a resultant decrease in output speed. And vice versa. The major types of gear tooth design used in modern transmissions and differentials are spur gears and helical gears. A heavy-duty standard transmission consists of a mainshaft and one, two, or three countershafts. Standard transmissions can be generally classified by how they are shifted. Sliding gear, collar shift, and synchronized shift mechanisms are used to effect shifts in standard transmissions. Synchronizers have two primary functions. First, they bring two components rotating at different speeds to a single, synchronized speed; and second, they lock these components together. Block or cone and pin synchronizers are the most common in heavy-duty transmissions. Most standard truck transmissions use mechanically shifted main sections: either a direct-actuated, shift tower assembly, or, in the case of COE trucks, a remote-actuated shift tower. Most current compounded transmissions use air controls to effect shifts in the auxiliary section, though some older trucks used gear levers for both main and auxiliary section shifts. An air-actuated gearshift system consists of an air filter and regulator, slave valve, master control valve, range cylinder, and connecting air lines. Auxiliary section gearing can be optioned to include a third gear in addition to the high- and low-range gears. This third gear is engaged or disengaged by a splitter shift system air activated by a button on the shift lever. A transfer case is an additional gear box located between the main transmission and the rear axle. Its function is to divide torque from the transmission to front and rear drive axles and, in addition, to option driving force to the front axle. The accessory drive requirements on trucks are met by using power takeoff (PTO) units. Hydraulic pumps for pumping loads off trailers and compressors for blowing loads off sealed bulk hoppers would be two examples of PTO-driven equipment. The six types of PTOs, classified by their installation, are side mount, split shaft, top mount, countershaft, crankshaft driven, and flywheel.

Summary (6 of 9) Synchronizers have two primary functions.
First, they bring two components rotating at different speeds to a single, synchronized speed. Second, they lock these components together. Block or cone and pin synchronizers are the most common in heavy-duty transmissions.

Summary (7 of 9) Most standard truck transmissions use mechanically shifted main sections. Most current compounded transmissions use air controls to effect shifts in the auxiliary section, though some older trucks used gear levers for both main and auxiliary section shifts. An air-actuated gearshift system consists of an air filter and regulator, slave valve, master control valve, range cylinder, and connecting air lines. Engine torque is transferred through the clutch to the input shaft of the transmission, which drives the gears in the transmission. The transmission manages the drivetrain. It is the driver’s means of managing drivetrain torque and speed ratios to suit chassis load and road conditions. A transmission enables the engine to function over a broad range of operating requirements that vary from a fully loaded standing start to cruising at highway speeds. Light-duty truck transmissions have a limited number of gear ratios and a single set of gears called main gearing, contained in a single housing. Most heavy-duty truck transmissions consist of two distinct sets of gearing: the main or front gearing, and the auxiliary gearing located directly on the rear of the main gearing. Auxiliary gearing compounds the available ratios in a transmission. Most heavy-duty trucks use at least one compound, some two compounds. Gear pitch refers to the number of teeth per unit of pitch diameter. The three stages of contact through which the teeth of two gears pass while in operation are coming-into-mesh, full-mesh, and coming-out-of mesh. The relationship of input to output speeds is expressed as gear ratio. Torque increase from a driving gear to a driven gear is directly proportional to speed decrease. So, to increase output torque there is a resultant decrease in output speed. And vice versa. The major types of gear tooth design used in modern transmissions and differentials are spur gears and helical gears. A heavy-duty standard transmission consists of a mainshaft and one, two, or three countershafts. Standard transmissions can be generally classified by how they are shifted. Sliding gear, collar shift, and synchronized shift mechanisms are used to effect shifts in standard transmissions. Synchronizers have two primary functions. First, they bring two components rotating at different speeds to a single, synchronized speed; and second, they lock these components together. Block or cone and pin synchronizers are the most common in heavy-duty transmissions. Most standard truck transmissions use mechanically shifted main sections: either a direct-actuated, shift tower assembly, or, in the case of COE trucks, a remote-actuated shift tower. Most current compounded transmissions use air controls to effect shifts in the auxiliary section, though some older trucks used gear levers for both main and auxiliary section shifts. An air-actuated gearshift system consists of an air filter and regulator, slave valve, master control valve, range cylinder, and connecting air lines. Auxiliary section gearing can be optioned to include a third gear in addition to the high- and low-range gears. This third gear is engaged or disengaged by a splitter shift system air activated by a button on the shift lever. A transfer case is an additional gear box located between the main transmission and the rear axle. Its function is to divide torque from the transmission to front and rear drive axles and, in addition, to option driving force to the front axle. The accessory drive requirements on trucks are met by using power takeoff (PTO) units. Hydraulic pumps for pumping loads off trailers and compressors for blowing loads off sealed bulk hoppers would be two examples of PTO-driven equipment. The six types of PTOs, classified by their installation, are side mount, split shaft, top mount, countershaft, crankshaft driven, and flywheel.

Summary (8 of 9) Auxiliary section gearing can be optioned to include a third gear in addition to the high- and low-range gears. This third gear is engaged or disengaged by a splitter shift system air activated by a button on the shift lever. A transfer case is an additional gear box located between the main transmission and the rear axle. Its function is to divide torque from the transmission to front and rear drive axles and, in addition, to option driving force to the front axle.

Summary (9 of 9) The accessory drive requirements on trucks are met by using power takeoff (PTO) units. Hydraulic pumps for pumping loads off trailers and compressors for blowing loads off sealed bulk hoppers would be two examples of PTO-driven equipment. The six types of PTOs, classified by their installation, are side mount, split shaft, top mount, countershaft, crankshaft driven, and flywheel.

Standard Transmissions

Similar presentations

Presentation on theme: "Standard Transmissions"— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Standard Transmissions

Similar presentations

Presentation on theme: "Standard Transmissions"— Presentation transcript:

Similar presentations

About project

Feedback