Axle

What is an Axle

An axle is a central shaft for a rotating wheel or gear.  In simple terms, an axle is a rod fixed to the centre of a wheel to help the wheel rotate. Without an axle, a wheel will have nothing holding it, therefore, it will not be able to rotate. The axle is sometimes attached to the wheels and made to rotate with them or, it could be fixed to the vehicle with the wheels made to rotate around it. In the case where the axle is attached to the wheels, extra components known as bearings or bushings are added to the point where they are mounted in order to regulate motion. In the case where the axle is attached to the wheels, a spindle is made.  This is the process where a bushing or bearing sits inside a hole in the wheel while the wheel rotates around the axle.

The axle is an essential part of any vehicle or truck, and it plays an important role in ensuring that the vehicle works correctly. The axle is what separates the wheels from each other and keeps an equal gap between them.  The wheels are the only parts touching the ground in many vehicles and therefore the axles holding them must be strong enough to be able to handle the weight of the vehicle and any load it may carry.

When dealing with cars and trucks, the word axle is often used incorrectly, sometimes when a remark is made about the shaft itself, the enclosure where the axle stays or when talking about an extended pair of wheels. In the correct context, a shaft which is attached to a pair of wheels and rotates along with them is an axle.

Axle in a Vehicle, Truck or Van

Axles are key components of any wheeled vehicle, because they serve essential functions which include transmitting driving force to the wheel and keeping a relative distance between the wheels and the body of the vehicle. The axles must also bear the weight of the vehicle itself, as well as the cargo of the vehicle.

In the case of a non-driving axle, also known as a front beam axle which is most often found in heavy-duty trucks and light vans, there will be no shaft and the axle will serve mainly for suspension and steering. In other cases, the axle serves only to provide driving force to the wheels and the position and angle of the wheel are handled by an independent suspension system. This is similar to the type of suspension you find in most new cars and SUVs, and on many light trucks

Structure & Design

Straight Axle

A straight axle is a single rigid shaft which holds the left wheel in a car to the right wheel.  A common axis of axle rotation exists between both wheels. This is designed to keep the wheel position steady even under substantial stress and also to support heavy loads.

These axles are commonly used in trains, at the rear of commercial trucks and on some heavy duty off-road vehicles.

Split axle

In the split axle, the wheel on each side is fixed to a separate shaft.  These axles are commonly found in modern passenger cars and this provides a smoother ride by creating an allowance for independent suspension on the left and right wheels.

Even in cases where the suspension is not independent, split axles allow the left and right drive wheels to be driven at differing speeds, while the vehicle turns with the use of a differential. This improves traction and extends tire life.

Tandem axle

This involves a group of two or more axles placed closely together, and trucks are built using this type of axle configuration to provide a greater weight capacity than what is found in a single axle. In smaller trailers, this type of axle is usually found in the rear.

Parts of an Axle

Axle Housing

A strong metal assembly which surrounds the axle shaft.

Axle Hub

The casting at the extreme of an axle shaft to which the wheel is attached.

Axle Hub Bearings

A roller bearing that sits between the axle shaft and the axle hub to help non-drive wheels rotate freely.

 Axle Nut

A special nut which is placed onto the end of a wheel spindle or axle shaft to protect the brake rotors and other components.

Axle Shaft

This is the shaft around which the wheel revolves, or in some cases, revolves with the wheel.

Axle Shaft Bearing

A roller bearing arrangement found at the point at which an axle shaft enters the vehicle’s differential or transmission.

Axle Shaft Seal

A circular seal, found at the point where an axle shaft enters the vehicle’s differential or transmission.

Axle Shims

Flat pieces of metal placed between the axle components to adjust free play.

Axle Support Bushing

Pieces of rubber designed to dampen naturally occurring vibrations when an axle shaft rotates within the axle housing assembly.

Axle Vent

These valves permit pressure changes inside a differential into which the axle shaft goes, they are also known as axle breather tubes.

Constant Velocity Joint

This is a universal joint placed on the ends of axle shaft and fitted into vehicles with independent suspension setups

Axle Plenum/Differential

A uniquely shaped piece found in 4-wheel drive vehicles that permits a progressive lockup of the differential.

Wheel Spindle

A short shaft located at the front wheels of rear wheel drive cars, and on which the wheel rotates

Wheel Spindle Bearing

This is a roller bearing assembly fitted around wheel spindles

Types of Axle

Drive Axle

Any axle driven by an engine is referred to as a drive axle.

The drive axle is a type of split axle with universal joints between the two halves of the axle and a differential. Each half of the wheel uses a constant velocity (CV) joint to connect to the wheel and this allows the wheel assembly to move freely in a vertical direction.

Dead Axle

Also known as the lazy axle, this axle is not part of the drive train but rotates freely. You can find this type of axle at the rear of a front wheel drive car and also on some trucks and trailers used for load bearing purposes

Lift Axle

Also known as the airlift axle or drop axle, some dump trucks and trailers are configured with this type of axle. This axle can be raised or lowered.  It is lowered to increase the weight handling capacity or to ensure even distribution of the cargo over more wheels, it is raised to prevent wear on the tire and axles.

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