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Axle Glossary | The A-to-Z List of Definitions

Axle components are sometimes described with multiple names for a single part. Also, one term can refer to multiple parts. To aid understanding, we provide this glossary of axle terms.

Whether you're performing a route axle bearing service, replacing a CV drive axle, or overhauling a complete rear axle assembly, you're going to come across numerous terms for Axles and Components. Depending on your knowledge and experience, many of these terms may or may not be elementary. However, because many products use different names for the one part, or one name for different parts, we've created this glossary to help you understand the basic axle components that exist.

Because no one is born knowing all these expressions, taking a quick look through this glossary can be helpful. When you do decide on what you need, CARiD offers a huge selection of original equipment style axle shafts, bearings, seals, shims, vent tubes, clips, and much more that match OEM factory specifications - for vehicles old and new.

Because axle components come in many variations, our website will guide you to those that are applicable for your vehicle once year, make, and model are entered in the Product Options Field. Choices that display after that point will be a proper fit for your car or truck. Certain items may ask for further details such as gear size/ratios.

If there was more than one external supplier that originally provided axle parts for your automaker, you may be prompted to choose which one. If you're not sure of any necessary details, we urge you to check your owner's manual or place a call directly to your vehicle manufacturer in order to find out.

In alphabetical order:

Axle Gasket:

See axle seal.

Axle Housing

Axle Housing

A rigid metal assembly that surrounds axle shafts. See solid axle setups for more details.

Axle Hub:

Axle Hub

The forging or casting at the end of an axle shaft to which a wheel is bolted onto. The end of the hub usually features splined teeth that will mate with those at the end of the axle shaft. The axle hub rotates with the wheel, and delivers driving force to the wheel bolted onto it. These are also described as wheel hubs.

Axle Hub Bearings:

Axle Hub Bearings

A type of roller bearing assembly that fits between the axle shaft and axle hub in order to allow non-drive wheels to rotate freely.

Axle Nut

Axle Nut

A specially designed nut that fits onto the end of a wheel spindle or axle shaft to secure brake rotors or other hardware in place. Depending on vehicle application, an axle nut may feature grooves that allow cotter pins to be used for attachment purposes. If the nut's sides, or flats, have become damaged, these are inexpensive to replace.

Axle Shaft

Axle Shaft

A shaft on which a wheel revolves, or that revolves with a wheel. Also known as a half shaft. Axle shafts come in many varieties, depending on vehicle application.

Axle Shaft Bearing

Axle Shaft Bearing

A type of roller bearing assembly located at the point where an axle shaft goes into the vehicle's differential or transmission. These keep an axle shaft supported and aligned properly while allowing it to rotate without friction buildup.

Axle Shaft Seal

Axle Shaft Seal

A round seal located at the point where an axle shaft goes into the vehicle's differential or transmission. It prevents fluid from spilling out of the gearbox as the axle shaft rotates. In some vehicles, the axle shaft seal also helps to keep the axle shaft in proper alignment. These are natural wear items and should be replaced any time they begin leaking, or when a shaft is removed for other reasons. Also known as axle gaskets.

Axle Shims

Axle Shims

These are thin pieces of metal that are placed between axle components to adjust free play. It may be typical that the shims are available in a variety of thicknesses in order to accommodate the required free play.

Axle Support Bushing

Axle Support Bushing

These are rubber bushing pieces designed to dampen vibrations that occur naturally when an axle shaft rotates within an axle housing assembly. Your vehicle may or may not have them - but if so, replace them any time axle work is done to ensure vibrations don't creep into your driveline over time.

Axle Vent:

Axle Vent

Also known as axle breather tubes, these check valves allow for pressure changes inside a differential or transaxle that the axle shaft goes into. As gear oil heats up during driving, pressurized air and moisture is allowed to escape. This relieves excess pressure buildup when that could blow out axle seals. Depending on vehicle application, axle vents may located directly on the differential housing, or very close to it on the axle housing assembly. If the vent piece becomes clogged or cannot function, moisture can become trapped inside the differential or transaxle - also contributing to breakdown of gear oil. It's important to replace these pieces whenever differential gear oil is changed, or when other related repairs are made.

CV Joint (Constant Velocity Joint)

CV Joint

A universal joint found on one or both ends of axle shafts fitted to vehicles with independent suspension setups. A ball-shaped piece on the axle shaft end(s) sits within cup-shaped piece attached to shorter shafts leading to the wheels or center mounting point. Ball bearings situated in between allow the CV Axle to change angles - pivoting at the joints as necessary when wheels articulate up and down over bumps. CV joints are mostly found on front-wheel-drive vehicles because they can best accommodate steering angle variations in addition to up-and-down wheel travel. CV joints are fully encased in a rubber boot in order to prevent the lubricating grease they are submerged in from escaping. Many modern rear-wheel-drive cars with independent rear suspension setups use CV joints at the ends of rear axle half-shafts as well as driveshafts.

CV Axle

CV Axle

An axle assembly that is sold complete with a CV Joint already attached to one or both ends. These may also be described as CV Axle Assemblies, or CV Drive Axles. They're found on virtually all modern front-wheel-drive cars as well as rear-wheel-drive ones with independent rear suspension.

Differential / Axle Plenum

Axle Plenum

A specially shaped piece within some Jeep "Vari-Lok" (a.k.a. "Hydra Lok") 4-wheel-drive differentials that allows progressive lockup of the differential. When one axle spins faster than the other, a pump produces pressure that activates a clutch that partially locks the differential while allowing some degree of slippage to avoid driveline binding.

Full-Floating Axle:

Full-Floating Axle

An axle design where the weight of the vehicle is supported entirely by a rigid, non-flexible axle housing assembly that surrounds the axle shafts. Two roller bearings support the weight of the vehicle, and the axle shafts themselves do not support any weight. This allows the axle shaft to be removed without unbolting the wheel. These are usually found on the rear of 4x4s. This type of axle can be identified by a protruding hub that the axle shaft flange is bolted to. A full-floating axle setup is considerably stronger than a similarly sized semi-floating axle.

Semi-Floating Axle:

Semi-Floating Axle

A type of axle setup that's more common on the rear of many half-ton (and lighter) 4x4s where the axle shaft supports the weight of the vehicle in addition to being the means of propulsion. Unlike a full-floating axle, in which each wheel hub is fully supported by bearings on both sides of the hub, a semi-floating axle uses a single bearing. And unlike full-floating designs, a wheel must be unbolted in order to remove the axle. Additionally, a broken axle shaft will result in the wheel coming off the vehicle.

Solid Axle:

A suspension setup where both front or rear wheels are connected by a single, rigid axle housing assembly that runs across the entire width of the vehicle. This does not allow left-and right-side wheels to articulate independently of one another the way an independent suspension setup does. These are commonly found on the rear of older cars as well as in the front and rear of most traditional 4x4s. Also known as beam axles or rigid axles.

Solid Axle

Stub Axle:

See wheel spindle.

Three-Quarter Floating Axle:

Three-Quarter Floating Axle

An axle design rarely used today where a surrounding axle housing supports all vehicle weight, but the axle itself is subject to torque loads only some of the time. Bearings are located between the hub and the axle housing.

Wheel Spindle:

Wheel Spindle

A short shaft on which a wheel rotates. These are typically located on front wheels of rear wheel drive cars, but are also found at the rear on vehicles with independent rear suspension setups. Also known as stub axles.

Wheel Spindle Bearing

Wheel Spindle Bearing

Roller type bearing assemblies that fit onto and around wheel spindles. They're located in the wheel hub on disc-brake wheels, and inside the brake drum assembly (which forms part of the hub) on drum-brake wheels.

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