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Technical Forum: Should sealed wheel bearing hubs be replaced individually or in pairs?


8/24/2010

Counterman magazine presents 11 technical and sales topics in an easy-to-read question-and-answer format.
 
Should sealed wheel bearing hubs be replaced individually or in pairs?
A. If one wheel bearing has reached the end of the road, chances are the wheel bearing on the other side of the vehicle may also be nearing the end of its service life, too. Both wheel bearings have racked up the same number of miles, so it’s logical to conclude that both sides have probably experienced the same amount of wear.

Based on this line of thinking, it would make sense to recommend replacing both wheel bearing hubs at the same time even though only one has obviously failed. On the other hand, some would argue replacing both at the same time would be an unnecessary expense. As long as the other wheel bearing is not making noise and play is still within specifications, it should remain in service. But the question is, for how long? 

Wheel bearings are engineered to go a lot of miles, and often last the life of the vehicle without ever being replaced (which may be upwards of 250,000 miles or more). However, their service life can sometimes be cut short by driving conditions and environmental factors.

Every time a wheel hits a bump or pothole, the wheel bearings take a pounding. The tire and suspension will cushion much of the impact, but it still adds up over time. A vehicle that spends much of its life driving on rough roads or cratered urban streets may wear out its wheel bearings in as little as 100,000 miles. Taxis, police cars and delivery vehicles can also wear out their wheel bearings rather quickly depending on how they are driven. Hard cornering puts a lot of side load on the bearings which they do not experience with normal driving. This can also accelerate wear and lead to premature bearing failure. Sealed wheel bearing assemblies are engineered to keep out contaminants. Even so, over time seals can wear and lose their elasticity, allowing road salt, moisture and dust to enter the bearing housing. Once inside, these contaminants can cause corrosion and wear, resulting in premature bearing failure.  Driving though standing water that is more than hub deep is another no-no that should be avoided because it can force water into the bearings.

Though sealed wheel bearings require no maintenance, there’s also no way to clean or regrease the assembly if it has become contaminated.  Replacement is the only repair option. 

Q.  When should a wheel bearing be replaced?
A.  The first sign of wheel bearing trouble is often noise (but not always).  A bad wheel bearing may make a rumbling, growling or chirping noise that changes with vehicle speed. The noise should be investigated without delay because a wheel bearing failure can sometimes allow the wheel to separate from the vehicle!

The noise produced by a bad wheel bearing will usually be  proportional to vehicle speed, and will not change in pitch or intensity when accelerating, coasting or decelerating (which is often the case with noise produced by worn differential, transmission or transaxle gears, or a bad U-joint). The noise may change when turning, or become louder or even disappear at certain speeds. But it shouldn’t be confused with the popping or clicking sounds produced by a bad outer CV joint on a FWD car. A bad outer CV joint usually only makes noise when turning, not when driving straight ahead. As a rule, sealed wheel bearings and hubs should have no play or roughness when a wheel is spun by hand. If a wheel bearing feels loose, or has play that exceeds specifications when measured with a dial indicator placed against the hub, it is worn out and needs to be replaced without delay.














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