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Problem: diagnosing unitized style wheel bearings

Cause: The sealed design of the wheel bearing sometimes makes identifying which bearing is the source of the complaint difficult.

Solution: There are a number of techniques available that can help pinpoint a failing bearing. They are listed below:

+ Test Drive

Wheel bearings can cause a number of different types of noises when driving. The noise will usually be more pronounced when the bearing is in a loaded condition such as in a turn.

+ Vibration Test

Failing wheel bearings will often cause a roughness when the wheel is rotated. The vehicle’s strut and spring act like an amplifier and allow easy diagnosis of a rough bearing. Place your hand on the spring and rotate the wheel assembly. A rough bearing will produce a pronounced vibration through the spring. Repeat the procedure on the opposite side.

+ Stethoscope Test

Failing bearings will often make a noise when they start to fail. The noise is not always easy to identify. The use of a stethoscope can make pin-pointing the problem bearing easier. With the vehicle on the rack and in gear place the stethoscope on the knuckle as close to the bearing as possible. A dry or failing bearing will produce a noticeable hum or grinding sound. It may be necessary to turn the wheel slightly to duplicate the bearing noise on the rack.

CAUTION: Extreme care must be taken when working near a rotating wheel.

+ Isolation Test

In some cases it will be necessary to isolate the bearing to determine its condition. On most FWD vehicles this is a relatively easy process. Remove the caliper and rotor. Disconnect the outer tie rod end and low ball joint. Remove CV axle nut. Disconnect knuckle from lower ball joint and remove CV joint from hub. Bearing is now isolated. Rotate the bearing while feeling for roughness.
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