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How Car Stuff Works

Mar 28, 2006 - 11:25:00 PM - Print

Wheel Bearings What Are They?

Wheel bearings perform two very important jobs in a vehicle’s suspension. The wheel bearing allows the wheels to rotate with minimal function, and they also support the vehicle’s weight.

To be able to do both of these jobs, the bearings must be in near perfect condition. The seals must also be leak free to keep the lubricant inside the bearings and contaminants out.

In an average sedan that weighs around 3,400 –lb, each pair of front wheel bearings, as well as the rear wheel or axle bearings, each support 850 pounds. This all depends on the front to rear weight distribution of the vehicle. It’s a lot of weight that needs to be supported over tens of thousands of miles.

Although wheel bearings are engineered to last 150,000 miles or more, the constant load does take a toll on the bearings, the grease and on the seals. If a wheel bearing fails prematurely, it is as a result of misadjustment, contamination or loss of grease.

Once a seal starts to leak, the bearings are in trouble. A damaged grease seal can allow grease to leak out of the bearings, therefore dirt and water can then enter the bearing cavity.

If the seals on sealed bearing assemblies fail, the seals cannot be replaced separately, the entire hub assembly needs to be replaced. Yet, in some older vehicles, a bad seal can be replaced with a new one to extend the life of the bearings.

Water is the worst thing for bearings as it causes it to rust and it contaminates the grease. The majority of vehicles’ wheel bearings seals are not designed to keep out water that is exerting pressure against the seal.

Therefore any vehicle that has been driven through hub-deep water should have its wheel bearing cleaned and repacked with fresh grease. Obviously with sealed wheel bearing assemblies, this won’t be possible, so the only thing to do is check for noise and play.

The first symptom of wheel bearing trouble is noise. There is usually a rumbling, growling, chirping or cyclic noise of some kind that will come from the vicinity of the wheels.

This is a good indication that trouble is now brewing and therefore immediate attention is needed. If you ignore a noisy wheel bearing it could suddenly fail. This could be fatal as the vehicle could lose a wheel while driving.

Wheel bearing noise doesn’t change with when accelerating or decelerating but it may change when turning, or it could even become louder or even disappear at certain speeds. But don’t get confused with the noise a bad outer CV joint makes, as it only makes a noise when turning.

Bearing play can often allow the steering to wander. This is often mistaken for worn steering components or even the wheel alignment being out.

Wheel bearings that are not factory sealed do require periodic maintenance. They should be cleaned, inspected and greased at about every 30,000 miles or according to the manufacturer’s recommendations.





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