Low/high speed grinding sound

[Henn28]

Well that sucks Aidzer, but at least you know now. And as long as the driveshaft is out you can do the splines if they look suspect, and the giubo. There is also a very good thread here about the driveshaft/giubo spacer route guys take to resolve the spline issue. Since you’ll have the motor up off the mounts, I’d pop new engine mounts in too if they haven’t been done.

The Bentley manual diff replacement instructions are pretty good, except you don’t necessarily need to remove the left engine mount, if you aren’t going to replace it. The top aft bolt on the diff is the long one and won’t come out because the subframe/mount is in the way. Stupid design. The other three are much shorter and don’t have clearance issues. Regardless, you can work the diff out and then the new one back in with that long bolt in the diff, or if you get the motor high enough (several inches) you can at least get the bolt all the way out of the diff with the space made between the diff and the top of the mount. You can also loosen all 4 bolts, although some are easier to access than others. Extensions, wobble heads and universal joints will be needed in various combinations.

As far as getting the diff in and out, it’s heavy and needs to go up into its “area” head-first and towards the back of the oil plan/subframe area, then rotate 90 deg or so, then move forward so you can get two bolts started to hold it in. It’s at least 45 or 50 lbs so I got it started upwards with a floor jack, but the rest was bench pressing. All while trying not to damage the outside seal, or the inner o ring seal that is supposed to be protected by a flimsy metal sliding ring (presumably slides back to expose the o ring as you torque the diff into the oil pan). The metal ring kept on popping off as I wrestled the diff into place. No leaks though so it’s tougher than it looks I guess.

An engine hoist would be best for lifting the motor a little bit at a time, and two floor jacks on either side will allow you to drop the sub-frame easily onto jack stands. I’d shoot initially for about 2 or 3 inches down on the subframe, and about the same on the motor, but in increments. The subframe is held up by six torx head bolts and has a guide pin on the unibody to help get it back up into place easily. You may need a little trial and error as you find the right amount of space between the motor and the subframe to maneuver the diff out.

Finally, one of the guys here recommended Amsoil severe gear oil in the collapsible bag. The filler hole is a bit hard to get to, so the collapsible bag worked like a champ for me. Three bags were more than enough for the front and rear diffs. I think each bag is 1 quart, delivered to your door. The plugs can be a pain, and mine did come out finally, but I’d recommend ordering new ones. They take a giant hex head for some bizarre reason. Another tool that only has one use…thanks BMW. The good news is now I have a whole set of mostly useless giant hex head drivers.