This section examines the rear-wheel drive differential.
A rear wheel drive differential uses bevel gears at right angles to each other inside the differential case.
The two smaller pinion gears are mounted on a driving pin passing through the case. They are constantly engaged with two larger side gears, located in recesses.
The side gears are splined internally to receive the inner ends of the axle shafts.
When the vehicle travels in a straight line, the ring gear rotates the case. The driving pin and pinion gears rotate end over end, turning the side gears with them, and the drive shafts.
There is no relative motion between the pinion gears and the side gears: each side gear turns at the same speed.
As soon as the vehicle turns from a straight ahead position, the inner wheel slows down and its side gear turns more slowly than the differential case.
The turning effort applied to the driving pin, forces the pinion gears to rotate slowly on the pin. They walk around the inner side gear while still being turned end over end.
This rotation of the pinion gears makes the outer side gear, and its road wheel, speed up by an equivalent amount. The outer side gear then turns faster than the case.
This provides an equal turning effort to each drive shaft while allowing for their speed difference.
In this standard type differential, traction occurs only if both wheels can grip the road surface.
If one wheel spins, the other cannot drive the vehicle - because of the differential action.
