928Myles

Hi, 1990 S4 auto with 107,000km (70,000 ml).
Once in D,2,3, or R and stationary at idle with foot on brake I have begun to notice a slight 'dry bearing' sound and vibration through the foot rest. Does not do it in P or N. Occurs when hot & cold. Have not noticed it once moving.

PO replaced TT with 2nd hand unit at some stage. MM's done recently. TB play checked 5000km ago and within limits (just). Auto fluid & filter changed recently.

Any ideas what this might be?
How much of a concern is it?
Where do I start looking?

Many thanks,
Myles Garmonsway

piccardo

Tough to pinpoint these vibrations, I had a noise like the one you describe but in park and at idle that ended-up being the flex plate. I just picked up another vibration at 3k rpm and im told the motor mounts are suspect so they are next on my list.

Mrmerlin

you might check the heat shields front to back
See if it maybe a throttle cable is rubbing or the bowden cable housing might be as well.
What was the last thing you did to the car that would be a good place to look, also check all of the exhaust hangers and recheck the motor mounts and see if the motor mount stud that comes out of the bottom of the crossmember is rubbing on the top of the steering rack.

928Myles

Thanks for the suggestions.
This vibration happens when stationary and only when in gear so I think that items rubbing is unlikely (unless the cable position alters enough to rub). I had not done anthing to the car immediately before noticing the sound but will check through your list of things Mrmerlin.
My gut feeling is that the TT bearings or TC bearings but I have no experience of either.

Thanks,
Myles

Charley B

You can relax a little. If it were these items you would hear and feel it the same in Park or Drive. The torque tube turns with the flywheel not the transmission. Mr Merlins suggestions are more likely and a lot less expensive.

WICruiser

The difference between N/P and in gear is basically load on the drive system. You don't say where the dry bearing sound seems to be coming from. The added load on the drive system "torques" the engine mounts slightly and moves the engine and all the attached stuff like exhaust pipes etc. accordingly. Some of these movements are different / no noticable when under motion. I would check for any contact points.

bernard farquart

I know this is probably going to be shouted down, but I would continue to drive it until the sound got worse, and thus easier to locate. But, what do i know, I had to rebuild my torque tube twice.

928Myles

Thanks for the reassurance Charley & Roger. I will hunt for a source this w/e. If I can't find anything I will take Bernard's suggestion and drive it until the source is clear.

Cheers,
Myles

WallyP

Find a way to SAFELY get under the car with it idling in Drive. If the source isn't quickly apparent, a one-meter piece of rubber or plastic tubing stuck in your best ear might help as a locator. Adding the earpieces from a stethoscope to the tubing is even better.