ShakyA4

My new A4 3.0QS Tip vibrates. I have had the tires balanced multiple times on a Hunter 9700 Road Force and they look great. Here are the symptons. At around 40MPH, the passenger seat rocks back and forth and the car feels jittery. As I drive up and down through 40 MPH, sometimes it is worse than at other times. It can vary somewhat with load. Yes, if still does this with the tranny in neutral. At highway speeds better than 70 MPH and building. You can almost hear a slight booming or buffeting like sound from the rear. The entire car feels shaky and you can feel it in the seats and see it in the visors as they shake. My 2000 Jetta is much, much smoother than this car. I get the sense that if i try to run the A4 up to 100MPH, it just may shake itself apart.

I am convinced it is not tires or wheels as my winter set does the same.

What should I have the dealer do?

If it is a driveshaft imbalance, would attaching hose clamps to it on a trial and error basis help to find the problem as we did in the old days?

Thanks for all of your help.

smallTTs

40 mph is the right speed for a vibration at wheel speed. It should be worse at double that, but milder between those speeds.

IMO, not driveshaft. I suspect a half-shaft, or maybe even something in a brake rotor that's turning at wheel speed. You didn't mention any steering wheel shake, so I'm guessing rear only.

If it is load sensitive, I'm even more inclined to a half-shaft joint.

Has it always done this? How many times have you had the dealer work on it? If not at all, take the service person for a ride and demonstrate the vibration. I'm guessing that they will look closely at the rear half-shafts.

Keep us informed.

ShakyA4

Jon,
Thanks for the response. There is not wheel shake. Yes, it has always done this. I have played with air pressure, etc. and wheel balance but no real effect.

The rear half shafts are just simple axles...How can they be the problem?

Thanks

Rich

smallTTs

four chances for your problem.

Something's not right and your dealer evidently hasn't found it. Insist that they find the problem. You might try another dealer's service department.

Just a hunch: do you have stock wheels for your summer tires?

ShakyA4

yes, Stock wheels and Dunlop 9090 tires. So you suspect a u-joint problem on one of the rear axles?

How do I instruct dealer to diagnose. They are not very competant plus they are the only one within 2 hours.

smallTTs

Take the Service Manager for a ride and demonstrate the vibration at both 40 and 70 or so mph. If SM agrees that there is a problem (first big step! You may have to go to the General Manager or owner of the dealership. Try "nice" first). Tell SM it occurred with winter tires and wheels, which I assume are aftermarket, and stock factory wheels/tires.

Stop right here if you mounted winter tires on original stock wheels; in that case it COULD be one bad wheel. This is unlikely unless one wheel has been damaged by hitting something which put a flat spot in the rim. This is common with aluminum wheels but you have to wack something like a large pothole pretty hard. The damage can be easily noted when the wheel is mounted on a balancing machined and rotated. You might not remember doing it, but if they find a flatted wheel, they could slip another TT wheel on your car to test drive.

Assuming you used different wheels for winter tires, offer to take in the other set for them to try. Their first tests should be to eliminate tires as a source of the vibration. Be sure to tell them you have had the tires rebalanced several times with no effect. Bent wheel vibration can't be balanced out.

I would insist on a loaner while they are working on your car. Sometimes that keeps them on task; they want the loaner back, so you car doesn't sit around.

My $.02. Good Luck!