The differential has three important functions,

To change the direction of the drive,

Provide a final drive ratio

Allow the wheels to move at different speeds.

It uses the following components to facilitate this,

diffs and axles technical info

Axle Technical Information


These are usually spiral bevel gears. The pinion is connected to the propshaft by a flange and supported by taper roller bearings. It drives the larger ring shaped crownwheel, the axis of which is at 90 degrees to that of the pinion, thus changing the direction of drive to the rear wheels.

Dividing the number of teeth on the crownwheel with those on the pinion gives the final drive ratio, eg 9 teeth on the pinion, 41 on the crownwheel, 41 divided by 9 = 4.55:1

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The crownwheel is bolted to a carrier, supported by bearings. Within this is a set of bevel gears. The larger (sun) gears are splined to the half shafts or output flanges.

Between them are 2 or 4 planetary gears, driven by a shaft located through the diff carrier.

They allow the wheels to move at different speeds when cornering.


The bearings locate the rotating gears.

Also as the crownwheel and pinion are loaded they push apart. This creates a side (axial) trust) which is resisted by the bearings. The axial load also stretches the casing so a pre load is applied to the bearings, usually by shims, so that the bearings do not have end float when under load. This would make the gears run out of mesh, causing them to be noisy and leading to premature failure.

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