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Old 01-06-2011, 12:28 PM
cn90 cn90 is offline
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Location: Omaha NE
Join Date: Mar 2006
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Mein Auto: 1998 528i 5-sp 140K+
Originally Posted by doru View Post
1. Did you preload the center bearing?
How do you do that? (For noobs like me...)
If you look carefully at the BMW Center Bearing anatomy, the ball bearing is surrounded by a rubber sleeve, itself suspended by a rubber boot (or ? polyurethane boot) that is attached to the metal holder.

This rubber boot allows some play in the bearing movement while preventing noise from entering the cabin.

When installing the new Center Bearing, one needs to preload the bearing toward the engine by 4-6 mm or so. This way when the car is lowered, the Rear Differential moves upward (in other words, the car body weight goes downward) and during that process, the Driveshaft moves forward a few mm. This is basically the fore-and-aft movement of the driveshaft when the car is lowered to the ground.

This preload procedure allows the Center Bearing to sit "perfectly" with little strain on it when the car is lowered to the ground.
Failure to do preload will kill the rubber boot very quickly.
On the other hands, if you never removed the wheels and raised the car via the tires (tires sitting on wood ramps for example) to do the repair, there is no need for preload.
The preload procedure was written for repair shop where the car is raised by the hoist for repair.
Here is a pic of premature rubber boot failure:

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Last edited by cn90; 01-06-2011 at 12:32 PM.
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