Axle hubs are devices used to attach wheels to the end of an axle or a trailer. The axle hubs also provide mounting locations for the braking components. Commonly attached to an axle by a splined connection, some axle hubs may be connected to an axle via universal joints (U-joints) or constant velocity joints (CV joints), especially in steering axle or independent suspension axle design. In trailer manufacturing, a full floating style hub is commonly used because of the superior strength of this style of hub. This style of hub is also used in performance vehicles and heavy trucks.
Most axle hubs are attached to the axle through the use of bearings and an axle nut. The bearings, typically roller bearings, ride in a bearing race that is mounted within the hub, while the axle is positioned through the bearing and the hub. The axle nut, a large castellated nut, is tightened to the recommended torque and locked in place with a cotter pin pushed through the castellations in the nut and the axle and is then bent over to prevent the nut from backing off of the axle threads. A bearing or axle cap is then snapped into place, covering the axle nut to maintain the axle grease inside of the hub assembly where it lubricates the bearing assembly.
These types of axle hubs are known as semi-floating and use the axle to support a portion of the load carried on the assembly. Another style of axle hubs, full-floating hubs, do not rely on the axle to carry any of the load. This type of hub is supported by two axle bearings and a stub axle mounted to the chassis of the vehicle or the trailer. This is the same hub assembly as used on heavy trucks and equipment. In a trailer application, these axle hubs require no axle at all, while in a drive axle assembly, the axle is attached to the hub via a drive plate or flange.
In some front-wheel drive vehicles, the axle hubs are part of a hub assembly that includes a wheel bearing as well as a splined drive flange. In this style of drive line, the axle hubs are changed as a unit when any single component of the assembly has failed and requires replacement. Maintaining proper service intervals and greasing is critical to the survival of any axle hub assembly. It is also critical that only high-temperature axle bearing grease be used to lubricate an axle hub.