A differential is needed so front or rear tires do not skid around a corner
A differential or sometimes called a rear driver was designed to allow the front or rear drive wheels of a car
to work independently of each other. This means that both wheels will transfer
engine power to each wheel while not being directly connected to each other. If a car did
not have this device when it went around a coroner the wheels would skid
because of the different distances each wheel travels. The outer wheel travels
further then the inner wheel. This action is possible by a set of 4 spider gears
which are located inside the 3rd member or carrier.
These gears are held in place by a pinion shaft and have each axle attached
to two of the spider gears. The main drive gear is called a ring gear and
together with the pinion gear is responsible for creating the gear ratio of the
final drive. These gears receive power from the output shaft of the
transmission. Gear ratios can be changed and are usually about 3 to 1 (3.0). The
drive shaft will turn three times to the one time the wheel will turn. Gear
ratios are used to multiply engine torque delivered to the drive wheels. Ring
and pinion gears are helical cut for smooth operation.
If one drive wheel looses traction neither of the drives wheels will transfer
power to the ground. As one wheel spins the other wheel remains stationary, this
is referred to as a dogleg. This condition is hazardous in snow and icy
conditions. To combat this issue a locker differential was developed in which
both axles can be locked together. In the image below we show this style of
traction device which is equipped with a weighted centrifuge that detects the
wheel slippage and engages the locking action by connecting the spider gears
The pinion gear sits at the front of the differential and is where the
driveshaft or final drive of the transmission is connected sometimes using a pinion yoke.
A crush sleeve is uses to set the bearing load of the pinion gear which is
determined by tightening the pinion yoke nut. On rear wheel drive cars a
driveshaft equipped with a U joint is used to transfer engine torque to the
differential. Gear oil is used to lubricate the gears and bearings inside the
differential. A magnet is featured inside the differential attached to the rear
cover are just inside the housing. This magnet is used to remove the metal
particulates from the gear oil which can be produced by the differential under
normal operation. The differential's gear oil level should be
checked and serviced
according manufacturer's recommendations.
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