Meaning | Concept | Definition:
An axle assembly on a car or truck is the set of components that allow the wheels to turn freely. Two wheels are usually connected by a hub known as an axle; it sits within an axle housing and is held in place by bearings and/or bushings that allow it to rotate within the axle housing.
Damage to the shaft itself can cause the entire assembly to fail, so the housing acts as a protective layer for the rotating shaft. Shaft lubrication is also possible thanks to the housing.
Two wheels are usually connected by a hub known as an axle; sits inside an axle housing.
The axle housing may also contain other components that allow for steering, driving, or load-bearing. If an axle housing is designed primarily to carry a load, it may be called a dead axle because it is not used to propel the vehicle forward.
Many front wheel drive vehicles feature a rear dead axle that is designed only to carry the load and to keep the left and right rear wheels on track. If the axle is part of the transmission system, it may be known as a driveshaft.
Sometimes an axle is not one solid piece, but rather two pieces that connect inside the axle housing. This allows the wheels to spin at different speeds; the gears that drive these wheels will be contained within the axle housing, as will the two separate axle pieces.
A driveshaft can also enter the housing at its front, usually in the center, to connect with any drive gears on the wheels. The casing allows these components to be protected from impact, and also allows the lubrication to be contained within the space, preventing premature failure of the axle components.
Larger trucks may have more than one axle to help support the weight of the vehicle without causing excessive stress on the axle. One axle is fully dedicated to supporting the weight of the truck, while the other axle bears no weight at all and allows the axle shaft to rotate with much less stress.
This is sometimes known as a full float axle system and is common on dump trucks, tractor trailers, and other large load-bearing vehicles. Semi-floating axles will end up carrying some of the weight of the vehicle, and non-floating axles are usually responsible for supporting the entire load of the vehicle.