Manual Transmission/Transaxle: Description and Operation

Manual transmissions are designated according to A, the number of forward gears, and B, the measured distance between the centerlines of the mainshaft and the countergear.

This transmission is representative of a synchronized constant-mesh transmission design. Fundamental components of this unit is the case, which houses the gears and shaft; the control cover, which houses the shifter mechanism; and the various shafts and gears. The input shaft has an integral main drive gear and rotates with the clutch driven plate; that is, the shaft rotates all the time the clutch is engaged and the engine is running. The input shaft is supported in the case by a ball bearing and at the front end by an oil impregnated bushing mounted in the engine crankshaft. The drive gear is in constant mesh with the countershaft drive gear. Since all gears in the countershaft cluster are integral to the shaft, they also rotate at the time the clutch is engaged. The countergear is carried on roller bearings at both ends and thrust is absorbed by thrust washers located between the countergear and thrust bosses in the case. The transmission mainshaft is held in line with the input shaft by a pilot bearing at its front end, which allows it to rotate or come to rest independently of the input shaft. In the 4-Speed 83 mm, it is carried in the rear bearing retainer.

Helical gears are incorporated throughout the transmission. The mainshaft gears are free to rotate independently on the mainshaft and are in constant mesh with the countershaft gears. The reverse idler gear is carried on a bushing finish bored in place, and thrust is taken on the thrust bosses of the case and extension for the 4-speed 83 mm. The transmission is fully synchronized in all forward speeds, however, reverse gear is not. The synchronizer assemblies consist of a hub, sleeve, two key springs and three synchronizer keys. The synchronizer hubs are splined to the

mainshaft and retained by snap rings. These assemblies permit gears to be selected without clashing, by synchronizing the speeds of mating parts before they engage.