1. Chapter 17
Torque Converters

2. Objectives (1 of 2)
Explain the function of the torque converter in a vehicle equipped with an automatic transmission.
Explain how the torque converter is coupled between the crankshaft and the transmission.
Identify the three main elements of a torque converter and describe their roles.
Define torque multiplication and explain how it is generated in the torque converter.
Objectives
After reading this chapter, you should be able to
• Explain the function of the torque converter in a vehicle equipped with an
automatic transmission.
• Explain how the torque converter is coupled between the crankshaft and the transmission.
• Identify the three main elements of a torque converter and describe their roles.
• Define torque multiplication and explain how it is generated in the torque converter.
• Define both rotary and vortex fluid flow and explain how each affects torque converter operation.
• Describe the overrunning clutch, lockup clutch, and variable pitch stators.
• Outline torque converter service and maintenance checks.
• Remove, disassemble, inspect, and reassemble torque converter components.

3. Objectives (2 of 2)
Define both rotary and vortex fluid flow and explain how each affects torque converter operation.
Describe the overrunning clutch, lockup clutch, and variable pitch stators.
Outline torque converter service and maintenance checks.
Remove, disassemble, inspect, and reassemble torque converter components.
Objectives
After reading this chapter, you should be able to
• Explain the function of the torque converter in a vehicle equipped with an
automatic transmission.
• Explain how the torque converter is coupled between the crankshaft and the transmission.
• Identify the three main elements of a torque converter and describe their roles.
• Define torque multiplication and explain how it is generated in the torque converter.
• Define both rotary and vortex fluid flow and explain how each affects torque converter operation.
• Describe the overrunning clutch, lockup clutch, and variable pitch stators.
• Outline torque converter service and maintenance checks.
• Remove, disassemble, inspect, and reassemble torque converter components.

4. Shop Talk
Torque converters can be confused with fluid couplings because both use similar operating principles.
The most fundamental difference is that torque converters use curved blades, while fluid couplings and fluid flywheels use straight pitch blades.
Torque converters also use stators and have the ability to multiply torque, neither of which is characteristic of fluid couplings.

5. Torque Converters
Automatic transmissions use a torque converter to couple the engine to the transmission.
The torque converter:
Transmits the twisting force or torque delivered to it by the engine crankshaft
Multiplies engine torque when additional power is needed
The amount of torque transferred from the engine to the transmission by the torque converter is directly related to engine rpm.

6. Torque Converter Construction
Truck torque converters can be:
Serviceable
Many torque converters are welded together. A normal service shop cannot disassemble them for servicing and repair.
Non serviceable
The only types of torque converters (T/Cs) that are readily serviceable are the types that are bolted together.

7. Flex Plate The flex plate carries the starter motor ring gear.
The combined mass of the torque converter and flex disc acts like a flywheel to smooth out the power pulses produced by the engine.
The flex plate also allows for a slight alignment tolerance between the engine and torque converter assembly.

8. Components The torque converter has three main components. Impeller
Turbine
Stator
Optional lockup clutch

9. Exterior
The exterior of the torque converter shell is shaped like two bowls facing each other.
They are either welded or bolted together.
A pilot shaft supports the weight of the torque converter at the front.
At the rear of the torque converter shell is the pump drive hub with notches or flats which are used to drive the transmission pump.
T/C Exterior
The exterior of the torque converter shell is shaped like two bowls facing each other and welded or bolted together (Figure 17–4). To support the weight of the torque converter, a short, stubby shaft, located in a socket provided at the rear of the crankshaft, projects forward from the front of the torque converter shell. This forms the frontal support for the torque converter assembly. At the rear of the torque converter shell is a hollow shaft with notches or flats at one end, ground 180 degrees apart. This shaft is called the pump drive hub; the notches or flats drive the transmission pump assembly. At the front of the transmission within the pump housing is a pump bushing supporting the pump drive hub and providing rear support for the torque converter assembly.

10. Curved blades rotate as a unit with the shell at engine speed
Curved blades rotate as a unit with the shell at engine speed. It starts the transmission oil circulating within the torque converter shell.
The impeller is positioned with its back to the transmission housing; the turbine is positioned with its back to the engine.
The hub of the turbine is splined so that it can drive the turbine (transmission input) shaft. The turbine shaft transfers engine torque to the transmission gearing.

11. The turbine blades are designed to have a greater curve than the impeller blades.
This helps reduce oil turbulence between the turbine and impeller blades–turbulence that would slow impeller speed and reduce the converter’s efficiency.
The turbine blades are designed to have a greater curve than the impeller blades. This helps reduce oil turbulence between the turbine and impeller blades, turbulence that would slow impeller speed and reduce the converter’s efficiency. Figure 17–6 illustrates how turbulence leads to a loss of energy and operating efficiency. For instance, when water strikes the flat surface of a teacup, it changes direction and moves back toward the oncoming flow. It splashes away from the flat surface in many directions; its energy is scattered. When the teacup is turned right side up, as in Figure 17–7, the water flow strikes the curved inner surface of the cup, which is similar to the curved surface of the turbine blades. In the teacup example, the curved surface helps direct and concentrate the water’s energy. As the water flows around the curve of the cup body, it pushes against the surface and moves away from the cup. The push of the water makes the cup a reaction member, just as the turbine is the reaction member in
the torque converter. A fundamental law of hydraulics states, “The more the moving stream of fluid is diverted (changed), the greater the force it places on the curved reaction surface.” Thus, oil in the torque converter moves around the turbine blades, pushing against the blades as it moves away and placing additional force on the turbine blade that drives the turbine shaft. The stator is located between the pump/impeller and the turbine. It redirects the oil flow from the turbine back into the impeller in the direction of impeller rotation, with minimal loss of speed or force. The blades of the stator are curved, so the stator side with the outward bulge is known as the convex side. The side of the stator blade with the inward curve is called the concave side. Figure 17–8 demonstrates the fluid dynamics of torque converter operation. During torque converter operation, the stator must lock when forced to turn in one direction and rotate when moved in the opposite direction. To make this possible, the stator is mounted on an overrunning clutch.

12. A fundamental law of hydraulics states, “The more the moving stream of fluid is diverted (changed), the greater the force it places on the curved reaction surface.”
As oil in the torque converter moves around the turbine blades, it pushes against the blades and transmits additional force.
The turbine blades are designed to have a greater curve than the impeller blades. This helps reduce oil turbulence between the turbine and impeller blades, turbulence that would slow impeller speed and reduce the converter’s efficiency. Figure 17–6 illustrates how turbulence leads to a loss of energy and operating efficiency. For instance, when water strikes the flat surface of a teacup, it changes direction and moves back toward the oncoming flow. It splashes away from the flat surface in many directions; its energy is scattered. When the teacup is turned right side up, as in Figure 17–7, the water flow strikes the curved inner surface of the cup, which is similar to the curved surface of the turbine blades. In the teacup example, the curved surface helps direct and concentrate the water’s energy. As the water flows around the curve of the cup body, it pushes against the surface and moves away from the cup. The push of the water makes the cup a reaction member, just as the turbine is the reaction member in
the torque converter. A fundamental law of hydraulics states, “The more the moving stream of fluid is diverted (changed), the greater the force it places on the curved reaction surface.” Thus, oil in the torque converter moves around the turbine blades, pushing against the blades as it moves away and placing additional force on the turbine blade that drives the turbine shaft. The stator is located between the pump/impeller and the turbine. It redirects the oil flow from the turbine back into the impeller in the direction of impeller rotation, with minimal loss of speed or force. The blades of the stator are curved, so the stator side with the outward bulge is known as the convex side. The side of the stator blade with the inward curve is called the concave side. Figure 17–8 demonstrates the fluid dynamics of torque converter operation. During torque converter operation, the stator must lock when forced to turn in one direction and rotate when moved in the opposite direction. To make this possible, the stator is mounted on an overrunning clutch.

13. Principles of Operation
As the pump impeller rotates, centrifugal force throws the oil outward and upward.
The faster the impeller rotates, the higher the centrifugal force.
Fluid under pressure is continuously delivered through the converter hub.
It is important to note that the oil pump delivering the fluid is driven by the engine.
A seal or combination of seals prevents fluid from being lost from the system.
PRINCIPLES OF OPERATION
As we stated at the beginning of this chapter, transmission oil is used as the medium to transfer energy from the engine to the transmission when a torque converter is used. Figure 17–9A illustrates what happens to the oil when the T/C impeller is at rest, and Figure 17–9B shows how the oil behaves when it is being driven. As the pump impeller rotates, centrifugal force throws the oil outward and upward. This is due to the curved Flat surface scatters shape of the impeller housing. (Remember the previous example of the teacup and water.) The faster the impeller rotates, the higher the centrifugal force. In Figure 17–9B, the oil is allowed to exit the housing without producing any measurable work. To harness some of this ‘lost’ energy, the turbine assembly is mounted on top of the impeller, as shown in Figure 17–10. Now the oil thrown outward and upward from the impeller strikes the curved vanes of the turbine, causing the turbine to rotate. The impeller and the turbine are not mechanically connected to each other. This characteristic differentiates a fluid coupling from a mechanical coupling. A hollow shaft at the center of the torque converter allows fluid under pressure to be continuously delivered from an oil pump. It is important to note that the oil pump delivering the fluid is driven by the engine. A seal or combination of seals prevents fluid from being lost from the system. Shop Talk There can be a mechanical connection between the impeller and turbine by the use of a lockup clutch. A lockup clutch eliminates slippage between the impeller and turbine at certain speeds. This helps to reduce the heat generated in the fluid and improves fuel mileage. The turbine shaft is located within the hollow shaft at the center of the torque converter. It is splined to the turbine and transfers torque from the torque converter to the transmission main drive shaft. Oil leaving the turbine is directed out of the torque converter to an external oil cooler and then to the transmission oil sump. When the transmission is in neutral, torque cannot be transferred from the engine to the transmission output because the powerflow between these two points has been mechanically disconnected. This does not mean, however, that the driver must physically place the transmission in neutral each time the vehicle is stopped. With the transmission in gear and the engine at idle, the truck can be held stationary by applying the service brakes. At idle, engine speed is slow. Because the impeller is driven by engine speed, it too turns slowly, creating less centrifugal force within the torque converter. The small amount of driveline torque generated can easily be held using the service brakes. When the accelerator is depressed, engine speed increases. Because the impeller is driven directly by the engine, its speed increases with engine speed. This increase in speed increases the centrifugal force of the transmission oil, and the oil is directed against the turbine blades. The force of the oil against the blades transfers torque to the turbine shaft and transmission proportional to engine speed. The faster the engine turns, the more force is applied. Torque converter efficiency is always highest when input speed (engine speed) is greatest.

14. Oil leaving the turbine is directed to an external oil cooler and then to the transmission oil sump.
At idle there is insufficient centrifugal force within the torque converter to move the truck.
As impeller speed increases the centrifugal force of the oil directed against the turbine blades becomes great enough to move the vehicle.
PRINCIPLES OF OPERATION
As we stated at the beginning of this chapter, transmission oil is used as the medium to transfer energy from the engine to the transmission when a torque converter is used. Figure 17–9A illustrates what happens to the oil when the T/C impeller is at rest, and Figure 17–9B shows how the oil behaves when it is being driven. As the pump impeller rotates, centrifugal force throws the oil outward and upward. This is due to the curved Flat surface scatters shape of the impeller housing. (Remember the previous example of the teacup and water.) The faster the impeller rotates, the higher the centrifugal force. In Figure 17–9B, the oil is allowed to exit the housing without producing any measurable work. To harness some of this ‘lost’ energy, the turbine assembly is mounted on top of the impeller, as shown in Figure 17–10. Now the oil thrown outward and upward from the impeller strikes the curved vanes of the turbine, causing the turbine to rotate. The impeller and the turbine are not mechanically connected to each other. This characteristic differentiates a fluid coupling from a mechanical coupling. A hollow shaft at the center of the torque converter allows fluid under pressure to be continuously delivered from an oil pump. It is important to note that the oil pump delivering the fluid is driven by the engine. A seal or combination of seals prevents fluid from being lost from the system. The turbine shaft is located within the hollow shaft at the center of the torque converter. It is splined to the turbine and transfers torque from the torque converter to the transmission main drive shaft. Oil leaving the turbine is directed out of the torque converter to an external oil cooler and then to the transmission oil sump. When the transmission is in neutral, torque cannot be transferred from the engine to the transmission output because the powerflow between these two points has been mechanically disconnected. This does not mean, however, that the driver must physically place the transmission in neutral each time the vehicle is stopped. With the transmission in gear and the engine at idle, the truck can be held stationary by applying the service brakes. At idle, engine speed is slow. Because the impeller is driven by engine speed, it too turns slowly, creating less centrifugal force within the torque converter. The small amount of driveline torque generated can easily be held using the service brakes. When the accelerator is depressed, engine speed increases. Because the impeller is driven directly by the engine, its speed increases with engine speed. This increase in speed increases the centrifugal force of the transmission oil, and the oil is directed against the turbine blades. The force of the oil against the blades transfers torque to the turbine shaft and transmission proportional to engine speed. The faster the engine turns, the more force is applied. Torque converter efficiency is always highest when input speed (engine speed) is greatest.

15. Shop Talk
There can be a mechanical connection between the impeller and turbine by the use of a lockup clutch.
A lockup clutch eliminates slippage between the impeller and turbine at certain speeds.
This helps to reduce the heat generated in the fluid and improves fuel mileage.

16. Types of Oil Flow (1 of 2)
The two types of oil flow that occur within the T/C are:
Rotary
Rotary flow describes the centrifugal force applied to the fluid as the converter rotates on its axis.
Vortex
Vortex flow is the circular flow that occurs as the oil is forced from the impeller to the turbine and then back to the impeller.
TYPES OF OIL FLOW
Understanding fluid flow within the torque converter during its operation is essential. The two types of oil flow that occur within the T/C are rotary and vortex (Figure 17–11). Rotary flow describes the centrifugal force applied to the fluid as the converter rotates on its axis. Vortex flow is the circular flow that occurs as the oil is forced from the impeller to the turbine and then back to the impeller. If a toy pinwheel were held at arm’s length and swung in a large circle, air movement at the outer circle would produce rotary flow, while the small circles cut by the pinwheel’s propeller vanes would produce vortex flow (Figure 17–12). As the speed of the turbine increases, it approaches the speed of the impeller that is driving it. The point at which the turbine is turning at close to the same speed as the impeller is referred to as the coupling point. Due to some fluid slippage that occurs between the turbine and the impeller, however, a true 1:1 coupling ratio is unobtainable unless some type of mechanical means is used to couple
the two components. A lockup clutch is used to achieve this.

17. Types of Oil Flow (2 of 2)
If a toy pinwheel were held at arm’s length and swung in a large circle, air movement at the outer circle would produce rotary flow, while the small circles cut by the pinwheel’s propeller vanes would produce vortex flow.
The point when the speed of the turbine approaches the speed of the impeller is referred to as the coupling point.
TYPES OF OIL FLOW
Understanding fluid flow within the torque converter during its operation is essential. The two types of oil flow that occur within the T/C are rotary and vortex (Figure 17–11). Rotary flow describes the centrifugal force applied to the fluid as the converter rotates on its axis. Vortex flow is the circular flow that occurs as the oil is forced from the impeller to the turbine and then back to the impeller. If a toy pinwheel were held at arm’s length and swung in a large circle, air movement at the outer circle would produce rotary flow, while the small circles cut by the pinwheel’s propeller vanes would produce vortex flow (Figure 17–12). As the speed of the turbine increases, it approaches the speed of the impeller that is driving it. The point at which the turbine is turning at close to the same speed as the impeller is referred to as the coupling point. Due to some fluid slippage that occurs between the turbine and the impeller, however, a true 1:1 coupling ratio is unobtainable unless some type of mechanical means is used to couple
the two components. A lockup clutch is used to achieve this.

18. Split Guide Rings
Fast moving oil exits the impeller blades, striking the turbine blades with considerable force.
It then has a tendency to be thrust back toward the center of both impeller and turbine.
To control this fluid thrust and the turbulence that results, a split guide ring is located in both the impeller and turbine sections of the T/C.
The guide ring suppresses turbulence, allowing more efficient operation.
SPLIT GUIDE RINGS
Power can flow through the converter only when the impeller is turning faster than the turbine. When the impeller is turning at speeds much greater than the turbine, a great deal of oil turbulence occurs. Fast moving oil exits the impeller blades, striking the turbine blades with considerable force. It then has a tendency to be thrust back toward the center of both impeller and turbine. To control this fluid thrust and the turbulence that results, a split guide ring is located in both the impeller and turbine sections of the T/C (Figure 17–13). The guide ring suppresses turbulence, allowing more efficient operation.

19. Stator (1 of 3)
The stator is the key to torque multiplication. It redirects the oil leaving the turbine back to the impeller.
The stator then redirects the fluid flow so that the oil reenters the impeller, moving in the same direction as the impeller.
The kinetic energy remaining in the oil now helps rotate the impeller with more force, multiplying torque.
STATOR
The stator is a small wheel positioned between the pump/impeller and the turbine (see Figure 17–3). The stator has no mechanical connection to either the impeller or turbine but fits between the outlet of the turbine and the inlet of the impeller so that all the oil returning from the turbine to the impeller must pass through the stator. The stator mounts through its splined center hub to a one-way, overrunning clutch, which is itself splined to a mating stator shaft, often called a ground sleeve. The ground sleeve is solidly connected to the transmission housing and therefore does not move. The stator can freewheel, however, when the impeller and turbine reach the coupling stage and the overrunning clutch unlocks. A stator can be either a rotating or fixed type. Heavy-duty truck torque converters use the rotating type. Rotating stators are more efficient at higher speeds because less slippage occurs when the impeller
and turbine reach the coupling stage. The stator is the key to torque multiplication. It redirects the oil leaving the turbine back to the impeller, which helps the impeller rotate more efficiently (Figure 17–14). Torque multiplication can occur only when the impeller is rotating faster than the turbine. This results from the velocity or kinetic energy transferred to the transmission oil by impeller rotation, plus the velocity of the oil that is directed back to the impeller by stator action. During operation, the oil gives up part of its kinetic energy as it strikes the turbine vanes. The stator then redirects the fluid flow so that the oil reenters the impeller, moving in the same direction the impeller is turning. This allows the kinetic energy remaining in the oil to help rotate the impeller even faster, multiplying the torque produced by the converter.

20. Stator (2 of 3)
The roller clutch is designed with an inner race, rollers, accordion (apply) springs, and outer race.
Around the inside diameter of the outer race are several cam-shaped pockets.
The rollers and accordion springs are located in these pockets.
As the vehicle begins to move, the stator stays in its stationary or locked position.
An overrunning clutch keeps the stator assembly from rotating when driven in one direction and permits overrunning (rotation) when turned in the opposite direction. Rotating stators generally use a roller-type overrunning clutch that allows the stator to freewheel (rotate) when the speed of the turbine and impeller reach the coupling point. The roller clutch (Figure 17–15) is designed with an inner race, rollers, accordion (apply) springs, and outer race. Around the inside diameter of the outer race are several cam-shaped pockets. The clutch assembly rollers and accordion springs are located in these pockets. As the vehicle begins to move, the stator stays in its stationary or locked position because of the wide difference between the impeller and turbine speeds. This locking mode takes place when the outer race attempts to rotate counterclockwise. The accordion springs force the rollers down the ramps of the cam pockets into a wedging contact with the inner and outer races. When the overrunning clutch is locked, the stator will be held stationary. As vehicle road speed increases, so does turbine speed until it approaches impeller speed. Oil exiting the turbine vanes strikes the back face of the stator, causing the stator to rotate in the same direction as the turbine and impeller. At this higher speed, clearance exists between the inner stator race and hub. The rollers in each slot of the stator are pulled around the stator hub. The stator freewheels or turns as a unit.

21. Stator (3 of 3)
Locking mode takes place when the outer race attempts to rotate counterclockwise.
The accordion springs force the rollers down the ramps of the cam pockets.
As vehicle road speed increases, turbine speed approaches impeller speed.
Oil exiting the turbine vanes now strikes the back face of the stator, causing the stator to rotate in the same direction as the turbine and impeller, unlocking the clutch.
An overrunning clutch keeps the stator assembly from rotating when driven in one direction and permits overrunning (rotation) when turned in the opposite direction. Rotating stators generally use a roller-type overrunning clutch that allows the stator to freewheel (rotate) when the speed of the turbine and impeller reach the coupling point. The roller clutch (Figure 17–15) is designed with an inner race, rollers, accordion (apply) springs, and outer race. Around the inside diameter of the outer race are several cam-shaped pockets. The clutch assembly rollers and accordion springs are located in these pockets. As the vehicle begins to move, the stator stays in its stationary or locked position because of the wide difference between the impeller and turbine speeds. This locking mode takes place when the outer race attempts to rotate counterclockwise. The accordion springs force the rollers down the ramps of the cam pockets into a wedging contact with the inner and outer races. When the overrunning clutch is locked, the stator will be held stationary. As vehicle road speed increases, so does turbine speed until it approaches impeller speed. Oil exiting the turbine vanes strikes the back face of the stator, causing the stator to rotate in the same direction as the turbine and impeller. At this higher speed, clearance exists between the inner stator race and hub. The rollers in each slot of the stator are pulled around the stator hub. The stator freewheels or turns as a unit.

22. Variable Pitch Stator
Each of a series of movable stator vanes has a crank rod fitted into a circular groove in the hydraulic piston.
The movement of a hydraulic piston varies the angle of the stator vanes.
Variable Pitch Stator
A variable pitch stator design is often used in torque converters in off-highway applications, such as aggregate dump trucks or other specialized equipment used to transport unusually heavy loads in rough terrain. Each of a series of movable stator vanes has a crank rod fitted into a circular groove in the hydraulic piston. The movement of a hydraulic piston varies the angle of the stator vanes (Figure 17–16). A constant low-pressure oil force is applied to one side of the piston while a valve directs a variable flow of high-pressure main oil on the other side of the piston. As the flow of high-pressure oil varies, the piston moves back and forth accordingly, turning the crank rods of each stator, which varies the stator angle. When high-pressure oil is applied to the piston assembly, the vanes rotate to a partially closed position (low capacity), which causes the torque converter to absorb less force. Because less of the available power is being absorbed by the torque converter, more of it is available to the power take-off gearing for operation of auxiliary equipment. When the oil pressure decreases to the point that the pressure-regulating valve reduces the amount of high-pressure oil being delivered to the piston, the piston moves back to its normal position, allowing the stators to rotate to their usual position (high capacity, fully open). This directs the available fluid power so that its energy can be most efficiently used.

23. Lockup Clutches
A lockup torque converter eliminates the 10 percent slip that takes place at the coupling phase of operation.
The engagement of a clutch has the advantage of improving vehicle fuel economy, lowering overall engine emissions, and reducing torque converter operating heat and engine speed.
LOCKUP CLUTCHES
Most modern heavy-duty trucks equipped with automatic transmissions have lockup torque converters (Figure 17– 7). A lockup torque converter eliminates the 10 percent slip that takes place between the impeller and turbine at the coupling phase of operation. The engagement of a clutch between the engine crankshaft and the turbine assembly has the advantage of improving vehicle fuel economy, lowering overall engine emissions, and reducing torque converter operating heat and engine speed. The lockup torque converter is a four-element (impeller, turbine, stator, lockup clutch), three-stage (stall, coupling, and lockup phase) unit. There are two types of lockup torque converters: centrifugal and piston. Piston lockups tend to be used in heavy-duty truck applications. A piston lockup clutch consists of three main elements: a piston, clutch plate, and back plate. These components are located between the torque converter impeller cover and the torque converter impeller. The piston and back plate rotate with the converter impeller. The clutch plate is located between the piston and the back plate and splined to the converter turbine. The engagement of the lockup clutch is controlled by the lockup relay valve that receives its lockup signal from the modulated lockup valve. The clutch apply pressure compresses the lockup clutch plate between the piston and the back plate, locking all three together. When the converter impeller and the turbine are locked together, they provide a direct drive one-to-one from the engine to the transmission gearing. The result is top vehicle speed performance and improved fuel mileage. As rotational speed of the output shaft decreases, the relay valve automatically releases the lockup clutch and standard torque converter operation resumes.

24. Caution
The torque converter is free to move forward when the transmission is disconnected from the engine.
To ensure that the torque converter does not separate from the transmission while the transmission is being removed from the vehicle, install a retaining strap to hold the T/C in position.

25. Lockup Clutch Back Plate
The back plate should be flat to within inch.
Inspect the football key slot for evidence of wear from movement of the lockup back plate and football key.
Excessive wear or elongation of the football key slot will require component replacement.
Inspect the back plate for cracks, from the key slot to the ID of plate.

26. Turbine Assembly
Inspect the turbine assembly for cracked or broken vanes and signs of overheating.
If the turbine assembly is taken apart, inspect the rivet holes for signs of wear or elongation.
The turbine assembly hub should be checked for stripped, twisted, or broken splines.
Turbine Assembly
Inspect the turbine assembly (Figure 17–29) for
cracked or broken vanes and signs of overheating. If
the turbine assembly is taken apart, inspect the rivet
Inspect the turbine assembly (Figure 17–29) for cracked or broken vanes and signs of overheating. If the turbine assembly is taken apart, inspect the rivet holes for signs of wear or elongation. Any damage noted usually requires component replacement. The turbine assembly hub should be checked for stripped, twisted, or broken splines. Any damage observed will require component replacement. Inspect the roller bearing journal for scoring, pitting, scratches, metal transfer, and signs of overheating. Slight irregularities can be removed with a crocus cloth. Inspect the selective turbine thrust bearing spacer surface for scores, scratches, burrs, and signs of overheating. Light honing is permitted to remove slight irregularities. Inspect the spline condition of the lockup clutch hub for notching due to lockup clutch plate movement. Replace lockup clutch hub if splines are notched deeper than inch on any one side. If the turbine assembly is taken apart, inspect the rivet holes for signs of wear or elongation. Check the rivets for cracks or loose fit. Any damage noted will require component replacement. Replacement of the turbine, turbine hub, or lockup clutch hub (Figure 17–29) will require replacement of rivets.

27. Lockup Clutch Piston Inspect the seal ring groove.
Check the lockup pinholes.
Inspect the friction surface for wear, scoring, scratches, signs of overheating, and flatness.
It should be flat to within inch TIR.
Inspect the seal surface.
Lockup Clutch Piston.
Inspect the seal ring groove of the lockup clutch piston (Figure 17–30) for cracked edges, nicks, burrs, and sharp edges; remove any slight irregularities with light honing. Pistons with cracked or chipped groove edges must be replaced. Check the lockup pinholes for signs of battering and elongation wear. Excessive elongation wear of the holes could indicate a wear condition of the lockup pins in the flywheel assembly. Excessive wear will require component replacement. Inspect the piston for cracks, warpage, and signs of overheating. Inspect the surface in contact with the friction plate for wear, scoring, scratches, signs of overheating, and flatness. The surface in contact with the friction plate should be flat to within inch TIR. Any damage noted will require component replacement. Inspect the seal surface for scratches, burrs, and nicks. Slight irregularities can be corrected with a crocus cloth.

28. Inspecting the Stator Assembly
Inspect the stator assembly.
Inspect the rivets for cracks or loose fit.
Check the stator cam roller pockets.
Inspect the stator thrust bearing race surface.
Check the stator freewheel roller surface, thrust bearing surface, and roller bearing surface.
Inspect the stator freewheel rollers.
Stator
Inspect the stator assembly (Figure 17–31) for cracked or broken vanes and signs of overheat. Any damage noted will require replacement of the stator assembly. Inspect the rivets for cracks or loose fit. Any damage noted will require component replacement. Replacement of the stator, stator thrust washer, cam, side plate washer, or stator cam washers will require replacement of rivets. Check the stator cam roller pockets for pitting, scoring, signs of overheating, and wear. Emery cloth can be used to clean up slight irregularities. Inspect the stator thrust bearing race surface for scoring, scratches, nicks, and grooves. Light honing is permitted to remove slight irregularities. Signs of overheating and metal transfer will require component replacement. Check the stator freewheel roller surface, thrust bearing surface, and roller bearing surface for scoring, scratches, nicks, and grooves. Light honing is permitted to remove slight irregularities. Signs of overheating and metal transfer will require component replacement. Inspect the stator freewheel rollers for scoring, scratches, grooves, and signs of overheat at bend. The freewheel roller springs should show no signs of cracks, distortion, overheating, or breakage. Any damage noted will require component replacement.

29. Pump/Impeller Pump/Impeller
Inspect the pump (Figure 17–32) for cracked or broken vanes and indications of overheating. Any damage noted will require component replacement. Next, inspect the pump-to-flywheel surface for nicks, scratches, or burrs that could cause fluid leakage between the flywheel assembly and pump assembly. Inspect the pump-to-pump hub gasket surface for nicks, scratches, or burrs that could allow fluid leakage when assembled. Light honing is permitted to remove slight irregularities.

30. Pump (Impeller) Hub (1 of 2)
Check the seal ring grooves on the pump hub for cracked edges, nicks, burrs, and sharp edges.
Inspect the front seal surface for scoring, scratches, nicks, and grooves.
No rework of any irregularities noted is allowed on the seal surface.
The use of a crocus cloth or light honing on this surface could promote leakage past the front seal.
Pump (Impeller) Hub
Check the seal ring grooves on the pump hub (Figure 17–33) for cracked edges, nicks, burrs, and sharp edges. Light honing is permitted to remove slight irregularities. Any cracked or chipped edges noted will require component replacement. Inspect the front seal surface for scoring, scratches, nicks, and grooves. No rework of any irregularities noted is allowed on the seal surface. The use of a crocus cloth or light honing on this surface could promote leakage past the front seal. Any irregularities noted will require component replacement. There should be no signs of cracks, scoring, metal transfer, or heat damage on the pump drive flange. You can remove any slight irregularities with light honing. Inspect the snap ring groove for burrs, cracks, and nicks (Figure 17–34). The snap ring must be able to lock securely in its groove. Check the bearing race surface for scoring, scratches, nicks, and grooves. Light honing is permitted to remove slight irregularities. Signs of overheating and metal transfer will require component replacement. Inspect the roller bearing bore for scratches, grooves, nicks, scoring, and signs of overheating. Inspect the gasket surface for nicks, scratches, or burrs that could allow fluid leakage between the pump hub and pump assembly. Light honing is permitted to remove slight irregularities. Inspect the pump hub for pulled, stripped, or crossed threads. Damaged bolt threads can be repaired.

31. Pump (Impeller) Hub (2 of 2)
There should be no signs of cracks, scoring, metal transfer, or heat damage on the pump drive flange.
Inspect the snap ring groove for burrs, cracks, and nicks.
Check the bearing race surface.
Inspect the roller bearing bore.
Inspect the gasket surface.
Inspect the pump hub for pulled, stripped, or crossed threads.
Pump (Impeller) Hub
Check the seal ring grooves on the pump hub (Figure 17–33) for cracked edges, nicks, burrs, and sharp edges. Light honing is permitted to remove slight irregularities. Any cracked or chipped edges noted will require component replacement. Inspect the front seal surface for scoring, scratches, nicks, and grooves. No rework of any irregularities noted is allowed on the seal surface. The use of a crocus cloth or light honing on this surface could promote leakage past the front seal. Any irregularities noted will require component replacement. There should be no signs of cracks, scoring, metal transfer, or heat damage on the pump drive flange. You can remove any slight irregularities with light honing. Inspect the snap ring groove for burrs, cracks, and nicks (Figure 17–34). The snap ring must be able to lock securely in its groove. Check the bearing race surface for scoring, scratches, nicks, and grooves. Light honing is permitted to remove slight irregularities. Signs of overheating and metal transfer will require component replacement. Inspect the roller bearing bore for scratches, grooves, nicks, scoring, and signs of overheating. Inspect the gasket surface for nicks, scratches, or burrs that could allow fluid leakage between the pump hub and pump assembly. Light honing is permitted to remove slight irregularities. Inspect the pump hub for pulled, stripped, or crossed threads. Damaged bolt threads can be repaired.

32. Summary (1 of 2)
Automatic truck (and passenger car) transmissions use a type of fluid coupling known as a torque converter to transfer engine torque from the engine to the transmission.
A flex plate, sometimes called a flex disc, is used to connect the torque converter to the crankshaft.
Transmission oil is used as the medium to transfer energy from the engine-driven impeller to the turbine, which in turn drives the transmission.

33. Summary (2 of 2)
Two types of oil flow take place inside the torque converter.
Rotary flow and vortex flow
A converter lockup clutch enables a mechanical coupling of the engine and transmission.