Originally Posted by eotiii
I have a 02 Lt with 25k on it. I have been changing the FD lube with AMSOIL gear lube once, sometimes twice a year. In the past, I have only seen fuzz on the magnet. This last time, there were a few shiny metal chips on it. The drive had no play and turns smoothly.
So I decided to take the drive to the dealer and have them rebuild it. They will clean it out and replace any bearings that are bad. I expect to pay $300 - $400 for the rebuild. The dealer said a complete new FD is now $1200.
Has any done the same thing and if so how successful was the rebuild?
Ask your service depart that is going to "replace any bearings that are bad" how they are going to calculate the shim thickness necessary to establish the preload for the new bearing (s).
Typically the problem with these drives is a failed crown wheel bearing and the tapered roller bearing is okay. If they plan on just replacing the crown wheel bearing using the existing shims, I'd suggest you pass on that rebuild.
There have been some reports of the tapered roller bearing spinning on its shaft/seat on the crownwheel but this seems to be a less common occurance and has occured on new year models.
If the tapered roller bearing is replaced, then the shimming of this bearing has to be calculated to create proper gear lash between the input bevel gear and the crown gear.
Whether the tapered roller bearing is replaced or not, if the crown wheel bearing is replaced the preload should be calculated.
Some of us have speculated that not all rebuilds of final drives (even those done by BMW service depts) have had preload calculated when a new bearing was fitted. It is much easier to just rebuild using the existing shim, but not a proper way to do it. A final drive rebuilt using this shortcut technique will work fine for many miles, but will probably eventually fail prematurely.
This may explain why some folks have had more than one failed crown wheel bearing, the rebuild didn't correct the initial problem.