955 Cayenne v6 Vibration at 80mph
 

Hello everyone, I currently have a 2006 cayenne base (v6 3.2l) and I just had the differential rebuilt as it was grinding due to bad bearings. I had a shop that specializes in transmission rebuilds for German cars. I picked up the car a few days ago and as soon as I drove off it felt like it was brand new car. When on the highway I was doing about 75mph and I felt the car start to vibrate at that speed and over. Before I had the differential rebuilt it had a grinding feel to it but never a vibration at high speeds. The vibration feels like it is coming from the driveline and you feel it in your seat, not the steering wheel so I don't think that it is tire related. I also got a road force balance and the ride improved, but the vibration is still there at 75-80. Any ideas on what could cause this? Thank you!

Check your Cardan shaft and bearing

I currently have 80k miles and had the cardan shaft replaced at 70K. Any other ideas?

Hmmmm.....that type of vibration to mean seems a balance or alignment issue somewhere in the driveline which is I was think driveshaft. I short on other suggestions

So do you think that the front driveshaft is out of alignment from when they reinstalled everything?

It's possible

Control arms. Probably lower, but your should do uppers as well if they have never been done either.

Vibration through the steering wheel is usually attributable to out of balance front tires. When the whole car shakes (seatbacks, etc) that's usually rear tires. A simple test, assuming you're not running a staggered tire setup, would be to swap your front and rear tires, drive it again and see if the steering wheel now shakes, but the car doesn't. I would think you'd pickup a driveline vibration before 75/80 MPH and this sounds like a tire balance or wear issue to me. While you have the tires off, run your hand along the circumference and see if you feel any cupping - cupped tires can have this sensation at speed too.

Yes, a wheel problem would be the simplest explanation. Combining that with the fact that the problem appeared out of the blue, I would first re-install the wheels. Loosen the lug bolts, then seat things and reinstall carefully, torquing to spec (currently an interesting thread on here regarding antiseize and torque settings for lug bolts).
https://rennlist.com/forums/cayenne-...-lug-bolt.html

If that does not help, try swapping wheels left-right, and even front-back to try to isolate which wheel (if any) is bad.

Or if you can't do that, I'm sure a tire shop will gladly give you new tires, new balance, rotation, wheel alignment, free coffee, you name it, etc., and you'll have to hope they did it right and did not break anything new.

If you can't do any of that and want to do a simple experiment, you could try letting some air out of the tires. Do that evenly for all 4 tires, and see if it affects the speed at which the vibration starts. If you do have a wheel balance / trueness issue, lower air pressure should give each tire just a little more compliance, delaying the onset of vibration and reducing it a little. That might be helpful in narrowing things down before you dive into chasing drive train issues.

I have a few updates, however the issue has not been solved yet. I had the tires rotated front to back, still didn't solve the issue. Had a hunter road force balance again, no bent rims and tires balanced normal. The only thing i was told was that my tread is on the lower side - 4/32 with about 30k miles on them. Had the driveshaft checked when the balance was done and there was no play where the carrier bearing / u-joint is. Car vibrates at exactly 80mph and has a humming noise, but at 75mph no vibration or noise and smooth ride. Could this possibly be bad wheel bearings? Any other ideas?

Is it at 80 and every speed higher or just at 80? If its at only a doecjfuc speed, it might be a harmonic resonance from something and that might be hard to get rid of. Move the cruise control up 4 MPH to 84.

Yes, It is at 80 and higher with a vibration in the seat/floor.

That sounds like something with the rear end. Front end would shake the steering wheel. Rear end shakes the seats and body.

Any idea on what could cause this in the rear end?