In trans-axles, the synchromesh unit plays a similar role. It is located between the end of each engagement sleeve and the gear.
In this layout, the engagement hub and sleeve for first and second gears is on the secondary shaft, as is the third and fourth speed hub.
The fifth gear engagement hub is at the end of the secondary shaft, furthest from the main drive pinion.
When first gear is selected, the engagement sleeve locks the first gear to the secondary shaft. When the clutch is released, the drive is transferred through the fixed first gear on the primary shaft, to the locked gear on the secondary shaft.
The secondary shaft rotation transfers the drive through the main drive pinion to the final drive ring gear and the differential case.
In first gear, the smallest gear on the primary shaft drives the largest gear on the secondary shaft, and this gives the lowest ratio. In this case, 3.4 to 1.
In second gear, a higher ratio is obtained as the fixed second gear on the primary shaft is larger. Fewer turns of the primary shaft are required to obtain one turn of the secondary. In this case 1.95 to 1.
In third gear, the engagement sleeve locks the freely rotating third gear to the secondary shaft. Drive is transferred from the fixed gear on the primary shaft to the locked gear on the secondary, and then to the final drive.
The drive transfer is similar for fourth gear.
The fifth gear ratio is provided by transferring the drive through the fixed fifth gear on the primary shaft, to the engaged fifth gear on the secondary shaft.
This is often an overdrive ratio, with the driving gear larger than the driven gear, making the driven gear rotate at a higher speed.
For Reverse, the reverse idler moves to mesh with a reverse gear on the primary shaft, and the matching-gear teeth on the outside of the first and second gear engagement sleeve.
Drive transfers through the idler to the splined secondary shaft sleeve. The idler between the shafts makes the secondary shaft rotate in the reverse direction. This reverses the direction of the final drive ring gear, and the road wheels.
