The wheel bearings are an important component because they reduce friction by allowing wheels to turn easily. They also support the weight of the vehicle. Most wheel bearings don’t require any maintenance because they are sealed assemblies on most late model cars and trucks. That means no need to repack the bearings with grease or to adjust bearing play. Even so, wheel bearings in many older vehicles do require periodic maintenance and adjustment — though they seldom receive it.
Sealed wheel bearings and hub assemblies in today’s vehicles will usually last up to 150,000 miles or more. But that doesn’t mean they last forever. Potholes, heat, friction and metal fatigue eventually take their toll and can cause a wheel bearing to fail. Water is especially hard on wheel bearings because it can contaminate the grease inside the bearing if the vehicle is driven through hub-deep water. For this reason, the wheel bearings on boat trailers should always be cleaned and repacked with grease every season.
SIGNS OF FAILURE
The classic symptom of a wheel bearing that is failing is cyclic noise. Most often a bad bearing will produce a chirping sound or a growl or a squeal that changes in proportion to vehicle speed.
If a bad bearing is suspected, the wheel bearings should be inspected to check for play or roughness. On late model vehicles with sealed wheel bearings or bearing cartridges, there should usually be little or no play when the wheel is wobbled by hand.
Wheel bearing play can be checked by grasping the tire at the 12 and 6 o’clock positions and rocking it back and forth. If any play can be felt, the bearings are loose and need to be replaced.
Spinning the tire by hand can also reveal bearing trouble. Any roughness that can be felt while rotating the tire, or any noise from the bearings would tell you the bearings are worn or damaged and need to be replaced.
CHECK FOR PLAY
The most accurate way to check bearing play is with a dial indicator. Place the dial indicator against the hub and rock the wheel in and out. As a rule, there should see no more than .005 inches of play if the bearings are good. Always refer to the vehicle manufacturer’s specifications as play can vary depending on the application.
If one wheel bearing is loose or noisy, all of the wheel bearings should be inspected because all have the same mileage. If one bearing is failing, chances are some of the others may also be nearing the end of the road, too.
Customers should be warned not to put off replacing a noisy or loose wheel bearing. Loose wheel bearings are potentially dangerous wheel bearings! If a wheel bearing seizes or breaks, the wheel can lock up or even separate from the vehicle.
The wheel bearings in most vehicles are designed for normal, light-duty driving. They are not designed to handle unusually high cornering forces or excessive loads. Consequently, many passenger cars and even some light trucks and SUVs have double ball bearing wheel bearings inside their hubs rather than stronger roller bearings. It’s a cost-cutting step that automakers use in many applications. But when a vehicle is driven hard and subjected to unusually high cornering loads, it puts a lot of strain on the wheel bearings and can cause premature bearing failure. This is a common occurrence on police cars, race cars, even taxis and delivery vehicles.
Sealed wheel bearing and hub assemblies may also have to be replaced if the ABS wheel speed sensor inside goes bad. Corrosion on the sensor rings inside the hub can cause an erratic wheel speed sensor signal. The ABS system doesn’t like this and will set a fault code and turn on the ABS warning light. Unfortunately, the fix isn’t cheap because the sensor is integral to the hub assembly and cannot be replaced separately on many such applications.
A sealed hub assembly with an integral ABS sensor should not be replaced, though, unless your customer is absolutely sure the fault is inside the hub and is not due to a wiring problem in the ABS sensor circuit. On older vehicles with serviceable wheel bearings, the bearings should be cleaned, inspected and repacked every 30,000 to 50,000 miles. There are still a lot of these older vehicles on the road, and the bearings on most are poorly maintained because few motorists know the bearings require maintenance. The only time the bearings receive any attention at all is when the vehicle is having a brake job, and even then the bearings might be skipped over if the technician is trying to cut corners to save time.
Serviceable wheel bearings need to be cleaned, air dried, then visually inspected for hairline cracks, flat spots, dimples, flaking, wear or damage. If a bearing race, roller or cage is bad, it has no business going back on the vehicle. The entire bearing assembly must be replaced.
