What Is a Rear Axle Assembly? Definition, Meaning and Concept

A rear axle assembly is a very large and heavy piece of steel and iron that is used to propel the vehicle by converting rotational force into linear motion. The driveshaft sends rotational power from the engine and transmission to the rear axle assembly differential. That assembly uses a ring and pinion gear assembly to convert rotational power into linear motion, turning the axles, tires, and wheels. The differential component of the rear axle assembly may be a separate and removable component of the axle housing, or it may be a permanently attached component of the rear axle with a removable cover to allow access to the gear assembly.

On most vehicles, the rear axle assembly is the second largest and heaviest component on the vehicle, second only to the engine block. The reason for the weight of the rear axle assembly is that this component not only supports the weight of the rear of the vehicle, but also supplies the propulsion aspects of the vehicle. The method of propulsion of any wheeled vehicle is usually the same.

Rotational power from the engine's rotating crankshaft is transferred through the transmission and sent to the rear axle assembly in a rear-wheel drive application. The drive shaft connects to the pinion yoke, which is actually the snout of the pinion gear. The pinion applies the power of rotation to the crown. This is the first step in converting to linear motion.

As the ring gear drives around the center of the rear axle package, it rotates the axles, wheels and tires with a driving force. The differential can be equipped with one of several types of differential packs, each with a particular feature. The most common type of differential carrier is the open carrier. This powers one drive tire, while the other remains free and de-powered. This type of differential sits on the average family sedan rear axle assembly.

The next step up in the performance-type rear axle assembly is the limited-slip differential. This allows both rear tires to receive power if the vehicle stalls. The most performance oriented of all the factory axle packages is the locker or locked carrier. This differential provides power to both rear tires equally and at all times. This differential only unlocks to allow the vehicle to turn a corner. In racing applications the rear axle assembly will commonly have a spool installed to permanently lock both axles at all times.