How a Differential Works

automotive differential

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.

spider gear

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.

pinion shaft

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 together.

ring gear locker

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.

gear oil level pinion yoke

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