In trans-axle designs, the drive is transferred through the clutch unit to a primary shaft.
In this example, the primary shaft carries gears of different sizes, meshed with gears on the secondary shaft.
Each pair has one gear fixed to the primary shaft and one free to rotate on bearings on the secondary shaft.
An engagement sleeve and hub, with a synchromesh unit facing each gear, is on the secondary shaft between first and second. And similarly between third and fourth.
The engagement sleeve moves to engage the dog teeth of the relevant gear when a gear is selected. This locks the gear to the shaft, so drive can be transmitted.
A drive pinion gear fixed to the end of the secondary shaft is constantly in mesh with a final drive ring gear. The drive is transferred through these gears to the differential unit.
A reverse idler transmits the drive from the primary to the secondary shaft when reverse is selected.
A five-speed transmission has an extra fixed gear on the primary shaft, meshed with a mating free gear on the secondary shaft.
The free gear has its own engagement sleeve and synchromesh unit beside it. Selecting fifth gear locks the gear to the shaft.
The gear on the primary shaft is larger than the gear on the secondary, so an overdrive ratio is provided. The secondary shaft rotates faster than the primary.
Gears constantly in mesh use helical gearing. Having the gearbox and final drive gears in one casing provides a compact and noise-free unit.
