Wheel bearing adjustment question.

[Brian Minkin]

What they are hunting for is loose wheel bearings which is a sign of impending bearing failure.  Bearing failure which will build up extreme heat could lead to a wheel departing the car while it is in motion.  A loose wheel bearing also will effect the handling of the car in cornering.  There is a static test for loose (worn out ) wheel bearings which is to raise the car on a lift and push and pull on the tires with your hands at a 12  and 6 position.  If you find a click or more movement your bearings are worn and should be replaced.  Acceptable movement is no more than 2mm. Simply tightening bearings that are loose will further push the bearings under preload into a worn out race and will still fail. You can also diagnose a worn out bearing from noise (a grinding sound when you rotate the wheels)  and even perhaps a rumble feeling in the steering wheel.

Once bearings show movement they are worn out and need replacement. Repacking will not help as the hard metal of the race is worn and pitted and the softer metal of the bearing cup will not hold up to the pressures placed on it. If inspection of the races  during repacking shows a darkening of the metal surface even if no pitting is evident  and no play was found this is also a sign of a worn out bearing.

Reasons for bearing failure are :

1. the lubricant has washed away or broken down due to failure of the seals

2. An outside contaminent has entered the bearing and scored or pitted the race.

3. A bad ground strap has caused static electricity arcing across the bearings and this has destroyed the race through electrolysis.

4. Miles and age

When I tech a car for RTR tech inspection I always check for bearing play and rotate the wheels to be sure there is no crunching sound coming from the bearings.  Our tech form ask the inspector if the bearings are in good condition and have no play.