A hub assembly is a critical set of components that together allow a car’s wheels to rotate smoothly while being able to move up and down with the suspension and swivel with the steering. The hub assembly connects the wheels, brakes, driveshafts (driven wheels), steering (front wheels) and suspension together allowing all to work as a system.
For front wheel drive cars the front hub assembly consists of a wheel hub carrier, the hub assembly and a wheel bearing. The hub carrier is mounted to the suspension and steering system and as its name suggests holds or carries the hub assembly. The hub assembly rotates freely within the hub carrier on the wheel bearing, which generally consists of an inner and outer set of roller bearings. Brake disks and wheel rims are bolted to the hub assembly. The driveshaft passes through a hole in the centre of the carrier to the hub assembly to provide drive to the wheels.
A rear non driven hub assembly is similar to the front although does not incorporate a driveshaft. In some cases the hub assembly may incorporate a stub axle. The bearing is more likely to be tapered race bearing and with inner and outer races often separated by a spacer.
Driven rear wheel hub assemblies are generally similar to that of a front wheel drives front in that they contain roller bearings and the carrier has a hole or hollow to allow the driveshafts to enter the hub. Similarly the undriven front wheels are similar to the rear wheels of a front wheel drive car.
For all types of car the hub assembly is located directly behind each wheel and is generally accessed with the wheel removed.
The most common cause of issues with the hub assembly is linked to the wheel bearings. Due to the high levels of wear they require routine maintenance as specified by the manufacturer. Generally speaking at some point in the vehicles life the wheel bearing will need to be replaced as the metal components are likely to wear beyond acceptable tolerances.
Other components that are likely to require maintenance or replacement include nuts and washers during routine maintenance of the hub assembly. Also for some cars dust covers, split pins and spacers may need to be replaced.
A useful preventative measure is to ensure that all wheels are fitted with hub caps or wheel trims as this helps to keep road grime and grit out of the hub assembly reducing the likelihood of premature wear and corrosion.