A4 in FF

I've been searching half heartedly for awhile for an answer but nothing seems quite right. I've got a 2000 1.8t manual. It started only under hard acceleration (full boost second gear was most noticeable) and now has worsened to the point it happens when the cruise is trying to maintain speed. It's a repeated rubber sounding (not metallic at all) thumping that SEEMS to come from rear passenger. It quits if you let off the throttle. It can not be felt in the shifter at all. It is not speed dependent, it's the same cadence wether you're at 30 or 80mph. This morning I had to turn around while heading to work and switch cars, it was so bad. I just replaced both rear wheel bearings and had hoped they may have been the culprit somehow. This morning before parking it I jacked it up and checked the rear diff, shafts and suspension components. They all seem tight. I did not check the drive shaft because the heat shield was in the way and I really needed to get going. I'm not really sure it's the drive shaft (or half shafts) though because the cadence never changes. Anyone have any ideas?

clancy

Just wondering whether it could be related to the motor mounts? If it only happens under torque or acceleration then if the motor mounts are shot and the engine twists or moves under power it then something is then rubbing or hitting or whatever only when the engine shifts. I'd look at the motor mounts and then for something that looks like it is rubbing or interfering with something. Fresh wear or a shiny surface or ??? Vague enough?

A4 in FF

It sure could be. I did check the front mount and it was ok. I didn't check the back mounts because I couldn't reach them with the way I had the car jacked up at the time. I did kind of dismiss them because I felt that I would feel that in the shifter, but I certainly could be wrong on that thought.

Brendon Taylor

its the driveshaft center support bearing, just had to do this to my car.... audi calls it a "non servicable part" but im stubborn, and its totally possible. part costs $35 on ebay, and its a bit of a bitch- take the driveshaft out, and you'll have to grind down a 17mm wrench on the box end so you can fit it into the small space inbetween the 2 parts of the split driveshaft. dont worry, it doesn't have to be pressed in (thank god) just remember/mark the position before you separate the driveshaft, make sure the new bearing isn't touching on both sides, and do your damnest to make sure its perfectly straight or you'll get a vibration after its all put back together

A4 in FF

I was starting to think this may be the issue and your certainty drives it home. I drove it last night with the windows down to see if I could pinpoint it better. I heard nothing on the road, but when I was parking in the driveway I heard very faint squeaking that sounded similar to a u-joint going out. It seems weird to me that the cadence of the noise wouldn't vary based on the RPM's of the shaft. I will post what I find when I check it out after work tonight.

A4 in FF

So how much play much play is there in a good center support bearing? I removed the heat-shield to get to it and found it didn't look torn up, but there was a 1/4" or better of play when I pushed up on the shaft. It seemed excessive to me, obviously it's designed to have some movement but how much is too much?

A4 in FF

I should clarify, the movement is in the rubber bushing around the bearing not the bearing itself.

A4 in FF

The problem is fixed, it was the center support bearing. The bearing itself was a little rough but the real problem was the rubber support that centers the bearing in the mount. I ordered one off eBay and had it swapped out in no time. Interesting side note on the repair, all the posts regarding splitting the driveshaft I read said they had to modify a wrench to remove the bolt, I didn’t have to. The boxed end of a 17mm fit just fine. So, to wrap this up, my symptoms were a dull thumping under hard acceleration, it did not change cadence regardless of speed and I could not feel it in the shifter.

clancy

Glad you solved it. Thanks for reporting back. Now when someone searches they will find your solution.

a4b512v

Having similar issues. The noise is as though someone is hitting the rear suspension with a rubber mallet. Occurs mostly when accelerating from a stop while turning in either direction. Thought it was right rear half shaft. Put a new 1 in, but the problem persists, but changed. Happens less on turns, more going uphill from a stop. Could be from me jacking at the rear diff. Will check the center bushing next. Thanks for the post!