Drive Train

Vibrations at High Speed

I had a high speed vibration last year. I did alignment and balance to no avail. Then I was told that high speed vibration normally comes from rear tires. Since I had already had the rear tires balanced, I thought I might "see" the vibration. So I jacked up the rear, put jackstands under the rear lift points, started the car, put it in gear and took a look. Guess what, I could see my differential jumping up and down. This was due to a bad inner CV joint.

I got a used half shaft from Dave Roberts and the vibration is gone. I also had a noisy rear bearing on the same side. I recently replaced the bearing. I couldn't tell you which one caused the other to fail, but I'll guarantee there was a relationship between the CV failure and wheel bearing noise. If you jack the car up and put it in gear, BE CAREFUL. That shaft can catch a piece of clothing and you'll be kissing the Weissach rear in a micro second.

Good luck,

Joe Rausa '89 S4 (smooth and quiet - except of course when you stomp it)



When I accelerate past 120 kph (approx 72 mph) I'm getting a strong vibration that shakes the entire car
and increases with intensity directly proportional to speed. By the time speed reaches 140 kph (approx 84
mph) it feels like the whole car is going to vibrate apart. (The vibration seems to be originating from either the middle or rear of the car but definitely not the front)

I've had the balance and general integrity checked on all four tires/wheels and they are fine and my
mechanic can find nothing obviously wrong when he looks around underneath (understandably, he's refused to road test it to experience the problem as he's not interested in adding to his ticket collection)

I don't know how long this problem has been there -- I hadn't driven the car this fast for a while but was recently in the outback and noticed it the first time the speed went past 120kph. There's no vibration at all below 120kph.

Anyone have any ideas what this might be coming from?

Robert Smallwood
86.5 928S AT



Check your half shafts (axles) i replaced one last year but i think i may have another bad one. I have new rims/tires and have a pronounced vibration at 80mph+. I thought it was my old wheels but the new set proved otherwise, so im deducing its the other axle.

On those lines, how would an axle assembly go out of balance, or cause such a vibration. I figure a bad CV joint but i have no other indications as far as i can tell that the joints are bad.

Tony
1987 S4 Auto 83k



Ive done this in the past to diagnose vibration in the drive train:

Assuming rear wheels are balanced OK (mine did this a bit at 160km/h recently but it was rear wheel balance) then sounds like could be the prop-shaft (torque tube?) from the clutch to the gearbox may have worn bearing, or bent last time you ran over a roo. Alternatively it could be rear half shafts.

Jack each side of rear end in turn (the other rear wheel still on the ground) up on secure axle stands and blocks under other wheels and spin the jacked up rear wheel with engine up to 60kph on the speedo and check if it vibrates. If not, take it to 120kph on the speedo and see. If it vibrates the same on both sides at 120kph its likely to be prop shaft, or if one side only vibrates at 60kph (wheel turns at twice speed coz of differential) then could be half shaft, loose rubber boot, or wheel balance.

Be careful that you have secure axle stands and chocks coz you have to do this with the handbrake off !!

Cheers,
Jeremy