In a conventional rear wheel drive, a beam axle assembly encloses the final drive gears, differential and axle shafts in one housing.
A crown wheel and pinion transfers the drive through ninety degrees, and provides a final gear reduction to the driving road wheels.
Hypoid bevel gears are normally used for this purpose.
Hypoid gears are a special design of spiral bevel gears, with the center line of the pinion below the center line of the crown wheel.
This reduces the height of the propeller shaft tunnel to give a flatter floor pan. The tooth shape provides a greater area of tooth contact, and therefore greater strength.
In this example, the crown wheel, pinion and differential gears are mounted in a differential carrier which can be separated from the axle housing.
Taper roller bearings support the pinion in the carrier. The companion flange splines engage with the pinion splines, to transfer the drive from the propeller shaft.
A collapsible spacer, between the bearings, allows a specified pre-load to be set, and depth of mesh shims position the pinion in relation to the crown wheel.
The crown wheel is bolted to the differential case, which is supported in the carrier by taper roller bearings, retained by bearing caps and bolts.
Threaded adjusting rings engage with threads in the carrier, and these are used to set the bearing pre-load and a back-lash clearance between the crown wheel and pinion.
With the carrier bolted to the axle housing, the splines on the axle shafts can engage with the splines of the differential side gears, and drive is transferred through the differential case and gears, to the road wheels.
