Rear axle parts can vary depending on the type of axle being used. Sometimes the axle situated at the rear of a vehicle is used as part of the drive system, while in other cases it is a dead axle, or one that does not drive the vehicle forward but instead simply helps support the weight of the car or truck. Some rear axle parts are fairly universal, however, as just about all axles will feature an axle housing as well as a spindle within that housing to allow the wheels to spin freely.
Drive components are rear axle parts that transfer power from the drive shaft to the wheels. This is usually done using a unit known as the rear differential. Several gears are mounted within the differential casing: one gear is attached to the drive shaft, which is situated perpendicular to the axle itself; the two axle shafts meet the drive shaft's gear within the differential housing, and they are subsequently spun by the drive gear. Each axle goes in a different direction: one reaches the left wheel, and the other reaches the right wheel. Each spindle and gear is contained within the axle housing to protect the rear axle parts from dirt, grime, and other potential sources of damage. Many other components may be contained within the differential housing, depending on the make and model of the unit and the added features of the vehicle.
Depending on the design, sometimes rear axle parts include bearings as well. These bearings usually surround the axle shaft itself and promote free movement of the shaft within the housing. This function allows the wheels to spin freely and prevents drag in the drive system. The bearings are usually located at either end of the axle, though the specific position can vary significantly depending on the axle's design. If the unit is a dead axle, it may be connected to the chassis of the vehicle by using U-bolts, which are heavy-duty bolts that wrap around the axle housing.
Some types of axles will feature more rear axle parts for specific functions. A portal axle, for example, is a unique system that raises the axle itself above the centerline of the wheels. This means the axle is farther off the ground than normal, giving the vehicle more clearance. These are usually used on off-road vehicles, and while they are very useful, the design means more components will be necessary at either end of the axle so torque can be transmitted to the wheels. Bearings and drive systems are often part of these axles.