Under acceleration there is a knocking coming from underneath the car. Mechanic says it is a driveshaft bearing. Is anybody familar with this repair?? The shop wants about $900 to fix. I'd like to try and get out cheaper. It's a manual tranny car, '86 635, and I am fairly mechanically inclined.

Sounds like a proper diagnosis. I had the same problem on my 740. The CV joins was bad too so I bought a whole rebuilt shaft ($400 from Thrash Driveshaft in San Antonio and so. CA). I suggest you pull the shaft first and look for other problems, if nothing replace the bearing. I have one I bought for my E32 that I'm pretty sure is the same (but please make sure) that I'll sell you. There's plenty of write ups on the procedure, mark the shaft before you take it apart so its still balanced later.

If you're fairly mechanically inclined you can do it. The driveshaft itself isn't the problem, it's wrestling the exhaust out that's tough (you have to remove it to get to the shaft). I used a lift which helped a lot, but I think it can reasonably be done without one.

If the center bearing is bad, it usually means one or more of the driveshaft UV joints have gone bad. They get a flat spot and bind, which excessively side loads the bearing and causes it to fail. If that's the case you have to replace the driveshaft too.

I got my driveshaft for about $300 from a place in Texas called Driveshaft Specialists and was impressed both with the driveshaft and with the people there. There's some controversy over whether it's better to get one with the original type non-greasable, non-replaceable staked UV joints or the replaceable joints with a grease fitting. I went with the staked type figuring that the shaft was engineered for that type and that the originals lasted over 100K miles.

While you've got the exhaust off, it's also a good time to redo the shift linkage and transmission mounts.

I got my driveshaft for about $300 from a place in Texas called Driveshaft Specialists.

Same place...they changed their name at some point. Good people, I've bought 2 from them.

Yep, they're good folks. And I liked the fact that they're an actual business rather than an internet website. They rebuild the shafts themselves rather than farming it out and doing a drop shipment.

Agreed. If there's no address and phone number on the site, I don't buy!

u can just replace the bearing yourself, its only 25 dollars, and u dont have to remove the exhaaust, ive replaced several, just undo the hangers and push it out of the way, its about a 2 hour job, when u have the driveshaft out inspect the u-joints, a bad bearing dosnt always mean u need a new shaft.

Thanks fellas. Are there any options as far as lightweight shafts or are they all pretty much OEM replacements?

I have access to a pit that I can drive over to work on the car, this should be adequate enough, yea?