In a manual transmission for a rear-wheel drive vehicle, the gear train is built up on three shafts.

The input shaft extends from the front of the transmission. An external parallel-splined section engages with internal splines on the clutch-driven plate.

A main-drive gear is an integral part of the shaft. It meshes constantly with a mating gear on a counter-shaft which has a number of gears formed on it.

These gears mesh with mating gears on the mainshaft, or output. These mainshaft gears are supported on bearings on the shaft. They can rotate without turning the output.

Each mainshaft gear has an external toothed section on one side. The teeth face an internally-toothed engagement sleeve located on a central hub, which is itself splined to the mainshaft.

The engagement sleeve can slide in either direction to engage the external teeth on the appropriate gear. This locks the gear through the sleeve and hub, to the mainshaft.

Before engagement of the components occurs, a synchromesh device between the sleeve and gear synchronizes them.



The gears constantly in mesh, have their teeth cut on a helix, at an angle to the gear center line.

This reduces gear noise and distributes load more evenly, as several teeth are in contact at any one time.

Teeth on the reverse idler are normally straight cut or spur gears, cut parallel to the gear center line.