Monday, August 25, 2008

1983 BMW 633 CSi: Drive Shaft Carrier Bearing


Rust not only destroyed the muffler system, it also has made this task much more difficult than expected. It's rusty enough to probably require some torch work and welding to remove the old carrier bearing mounting studs. From what we could tell, BMW welded stud bolts to the frame of the car. To these are mounted the carrier bearing brackets (see red arrow). That may have worked well at one point, but it's not working well now. Rust has eaten through one of the carrier bearing's two brackets and the frame to which it should be bolted is covered with rust. The mechanic was willing to try, but couldn't guarantee that it wouldn't turn into a $500 repair. So, I'll be driving it home tonight where I will attempt to do the job myself. At least that's the plan.

For someone who has never changed a U-bolt in his life, the big question is this. How is it supposed to be done? That called for some help from Google. After searching for a while, I tried Autozone's Repair Guide. Their advice covers several models, so it may not apply to the 633. But it's worth a read. Here's what they said:
To remove:
  1. Paint alignment marks on the drive shaft at the center bearing for installation back into its original orientation. It is critical for balance that the 2 halves of the drive shaft be replaced into their original relationship.
  2. Remove the drive shaft.
  3. Loosen the spline locking sleeve at the center bearing and separate the front section from the rear section.
  4. Remove the snap ring at the splines.
  5. Use a puller or press to remove the center bearing from the shaft.
  6. Note the location of the dust shields.

To install:
  1. Press the new center bearing onto the drive shaft. The dust shield should be flush with the center mount.
  2. Clean the splines and coat with moly type lubricant. Install the front half to the rear in the same position as it was removed.
  3. Install the drive shaft and tighten the spline locking sleeve to 12 ft. lbs. (17 Nm), except for 4-wheel drive which is 16 ft. lbs. (22 Nm). If not equipped with splines, use a thread locking compound and tighten to 70 ft. lbs. (97 Nm).
That seems to jive with what the mechanic was thinking. But thinking and doing it myself are two different projects. We'll see what happens.

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