Wheel bearings allow each wheel to rotate. There are several types of wheel bearings used in cars: some require no maintenance; others can be disassembled, cleaned, and inspected for wear.
Failing wheel bearings develop excess clearance, or play. One symptom that may develop when the bearing is put "under load" is a distinctive growling noise that can be heard when the wheels rotate at road speeds.
To replace wheel bearings located in the brake drum or brake rotor, the wheel is removed, as is the brake drum or brake disc. The wheel bearings are replaced and packed with fresh grease. If the wheel bearing is an integrated part of the vehicle's suspension, the suspension or wheel hub may need to be removed to ease wheel bearing replacement.