1. Manual Drivetrains and Axles
8th Edition
Chapter 6
Manual Transmissions Parts and Operation

2. Learning Objectives (1 of 2)
1.1 Prepare for ASE Manual Drive Train and Axles (A3) certification test content area “B” (Transmission Diagnosis and Repair). 1.2 Explain the construction of a manual transmission. 1.3 Discuss synchronizer operation. 1.4 Explain five-speed transmission torque flow.

3. Learning Objectives (2 of 2)
1.5 Discuss shifter operation. 1.6 Explain the construction of manual transmission gears. 1.7 Discuss the purpose of transmission case and bearings.

4. Purpose of Manual Transmissions
The purpose of the transmission is to provide neutral, forward gear speeds or ranges, and reverse.
It must be able to provide a gear ratio that is low enough, when multiplied by the final drive ratio, to increase the engine’s torque sufficiently to accelerate the vehicle at the desired rate.

5. Construction Power Paths
Parts: Cluster gear, input shaft, output shaft, reverse idler shaft
Shifting gears: constant mesh gears; speed gear
Gear ratios
Torque capacity

6. Figure 6–1 A five-speed transmission gear train.

7. Reverse
The transmission has to reverse the direction of rotation, requiring one more gear in the gear train.
When one external gear drives another, they will rotate in opposite directions.
Reverse idler

8. FIGURE 6–4 (a) The input shaft rotates in a clockwise direction; the countershaft rotates in a counter clockwise direction and the first–reverse gear drives the output shaft in a clockwise direction. (b) When meshed with the idler gear, the first–reverse gear will be driven in a counter clockwise direction. A simple (single) idler is shown.

9. Speed Gears
All gears on the countershaft are permanently attached to the shaft.
When the countershaft rotates, all gears on the countershaft rotate.

10. Synchronizers
To shift into gear, the driver disengages the clutch and moves the shift linkage.
As the sleeve moves, the detent keys help guide the stop ring toward the speed gear.
The stop ring acts as a brake to slow down the gear so that its speed matches the speed of the synchronizer assembly.

11. Figure 6–7 Typical synchronizer assembly.

12. Figure 6–10 The shape of the splines helps prevent the transmission transaxle from jumping out of gear during acceleration and deceleration.

13. Figure 6–11 Exploded view of a triple cone synchronizer.

14. Five-speed Transmission Torque Flow (1 of 3)
Neutral: all of the synchronizer sleeves are centered on their hubs.
First gear: the shift linkage slides the 1–2 synchronizer sleeve rearward toward the first speed gear.
Second gear: the shift linkage slides the 1–2 synchronizer sleeve forward, away from the first speed gear and toward the second speed gear.

15. Five-speed Transmission Torque Flow (2 of 3)
Third gear: the shift linkage centers the 1–2 synchronizer sleeve and moves the 3–4 synchronizer sleeve back toward the third speed gear.
Fourth gear: the shift linkage moves the 3–4 synchronizer sleeve forward, away from the third speed gear and toward the input shaft drive gear.

16. Five-speed Transmission Torque Flow (3 of 3)
Fifth gear: the shift linkage centers the 3–4 synchronizer sleeve and moves the fifth synchronizer sleeve toward the fifth speed gear.
Reverse: sliding gear and constant-mesh gear.

17. Figure 6–12 In neutral, the input shaft and the countershaft are rotating if the clutch is engaged (clutch pedal up), but no torque is being transmitted through the transmission.

18. Figure 6–13 In first gear, the 1–2 synchronizer sleeve is moved rear-ward, locking the first speed gear to the output shaft. Torque is transmitted from the input shaft to the countershaft and then to the output shaft.

19. Figure 6–18 Torque flows through the transmission in reverse gear
Figure 6–18 Torque flows through the transmission in reverse gear. Note that the idler gear drives the 1–2 synchronizer sleeve gear, which is splined to the output shaft.

20. Shifter Mechanisms
The shifter mechanism moves one or two synchronizer sleeves or gears to engage the desired gear speed.
During upshift or downshift, one synchronizer sleeve is moved to neutral before the sleeve of the desired gear is moved to engage the desired gear.

21. Figure 6–20 When the gearshift lever is moved, the internal linkage (shift rails) moves the shift fork and synchronizer sleeve to shift gear speeds.

22. Manual Transmission Gears (1 of 2)
Main shaft
Located by the rear bearing, bearing surface, and retaining ring.
Have a surface for the pilot bearing to the main drive gear at the front and the splines to match the U-joint splines at the rear.

23. Manual Transmission Gears (2 of 2)
Countershaft and cluster gear
The cluster gear is supported by the rod-like countershaft with a set of needle bearings at each end in older transmissions.
The fit between the countershaft and the case is tight enough to prevent lubricant leaks.
Most cluster gears are one-piece units.

24. Figure 6–25 Two gears, (3) and (4), are press fit onto the cluster gear in a TR-3550 transmission.

25. Transmission Case and Bearings
Usually made from aluminum castings; most have openings for access to gear train.
Bearings
Transmissions use a variety of bearings, and can include:
Needle (can carry large side loads), ball (can carry moderate to high side loads and thrust loads), tapered (can carry large side and thrust loads), bushings (support the driveshaft slip yoke).

26. Figure 6–26 A Borg-Warner T5 five-speed transmission shown with the shifter cover removed.

27. Manual Transmission Lubrication
What are the jobs of the lubricant for manual transmissions?
Viscosity
What are the gear oil classifications?
Synthetic lubricant
Lubrication inside the transmission

28. FIGURE 6–29 When selecting the specified lubricant to be used in a manual transmission, always check that the viscosity and the rating match factory specifications.

29. Summary (1 of 2)
Transmissions provide gear sets for forward speeds and reverse as well as neutral.
Synchronizer assemblies normally have a hub, sleeve, a set of keys, two blocker rings, and a speed gear on each side.

30. Summary (2 of 2)
Transmissions torque capacity is determined by the size of the gears and shafts.
Transmissions shifts use external or internal linkages that include detents, interlocks, and shift forks.