danglerb

Tire and wheels and vibration make me nuts.

Swap with a known good set of tires and wheels, make sure the mounting is done correctly. Isolating the problem is always my first step.

It could even be the new tires/wheels are actually smoother running than the old ones, so that you now notice something that used to be masked.

Good luck. (as in may the first thing you try be the right one).

Nicole

I'm getting vibrations from the rear - more when the car had been sitting for a longer time. It seems to get better after driving it for a while.

My first car in the US - an 89 Ford Probe LX - had vibrationis from the rear at about 70mph. They usually got worse after some time of driving. I went from tire shop to tire shop and learned about their incompetence and renentless hunger for selling me unnecessary stuff. I took it to the Ford Dealer, where I was told that I wasn't supposed to drive that fast anyway. Then, one day I mentioned it to the MIDAS shop around the corner from where I lived, and the manager took finding the problem as a personal challenge. Well, it was fairly lsimple: The rear brake dums were warped, but nobody had ever looked at that before...

danglerb

My dealer told me its the tire, a "slipped belt", which just made the tire guys laugh and tell me the tire is fine take it back to the dealer. Eventually it sort of went away, and I never did find out what was causing it.

4day tire stores used to have a device that used a grinder or cutter for two steps, trimming the tread for zero run out (perfectly round "as mounted on wheel"), then something on the side I think of the tread to make the rolling force from the sidewall flex constant. A good tire guy checks the runout when the tire is mounted, and remounts with the tire turned relative to the wheel until he gets the best fit and balance. Some shops also have a max amount of weights they put on before remounting in a new position.

Next new car I bought I found a dealer that owned the tire store too, unfortunately I never had a problem. ;(

Ispeed

The cayennes had some poorly cast wheels that vibrated and couldn't be balanced out, maybe the same problem?

greg928GTS

GEEEEZ.

I"m not sure of the technical aspects of what the guy is doing when he balances the tires on the Hunter, but I have the same guy do it each time, and he checks all sorts of things. The last time, he loosened one tire off the wheel and turned it about 180 degrees and then balanced it.

I don't have another set of tires and wheels anymore. That would be a good way to see if it's the tires/wheels.

When I have my wheels balanced, I always remove and install them myself. I have my own torque wrench to make adjustments after a few miles of driving.

As far as I know, the motor mounts have not been replaced. I'll have to check and see if the motor rocks when the throttle is blipped. My vibration problem really doesn't seem like the type that would come from motor mounts. It seems like it's from something turning, like wheels, rotors, wheel bearings, drive shafts, etc...

My steering rack seemed fine when I checked it.

Rear axles and CV's seemed fine when I checked those over. I had the car in the shop to "baseline" it earlier this year. That's when I had the wheels/tires changed over, and tried to fix my transmission problem. The mechanic and I checked everything we could think of in the suspension, front end, brakes, exhaust, steering, etc...

I don't know the procedure he used to replacing the rear wheel bearings. How does one tell if there's a problem with the wheel bearings?

I guess I'll bring it back in for balancing again and note how far out each wheel is.

I was thinking it could be flat spots on the tires from sitting in the shop. But don't those usually run out after 10 or 20 miles of driving?

AO

Greg-
It takes longer for those "flat spots" from sitting to round out in colder climates. Maybe you need to go for a longer drive!

bgrabner

Just an idea - possibly check the rotors if all else fails? I know it sounds far-fetched, but my truck had a bit of a vibration at 60-75 - the dealer swapped the tires front to back, and replaced the rotors because they were out of balance - sounds strange but it seems to have worked. I have never heard of a 928 having this problem, but the front rotors are pretty big...if one of them were off it may cause a vibration at speed i would guess...

Ispeed

I would recommend that we all do extensive speed testing mostly between 100 and 170mph to weed out any vibrations and trace the possible causes. I try to do this often, it's very important!!!

AO

Another good point. I believe the stock OE rotors use clip-on weights which can fall off or be thrown. The Zimmerman rotors I believe are ground to achieve balance. If a rotor is out of wack, the trick becomes finding out which one. The only way that you could be assured of having everything in balance would be by having the wheels balanced on the car, and there are very few shops/cars capable of doing that. Luckily our cars are setup for such a proceedure.

danglerb

Balancing on the car solves a lot of problems, but it can also temporarily mask a problem which comes back after a some normal tire wear.

Garth S

There is a counterbalance weight on the prop shaft within the torque tube of later cars ... IIRC: what are the symptoms if this loosens and begins moving back and forth on the shaft? ..... it may alter the node of vibration if incorrectly situated.

Dead motor mount induced vibrations can be felt in the seat when at idle on a cold start up ..... never seemed particularly bothersome at 160Kmph ....

Pfunde

Is your tyre a "v" or "w" ( 270km/h or 300 km/h ) If so, there's extra metal inforcement and harder compound, and therefore it's need's some heat after sitting for even a day before it's ok. Therefor, take a drive to get some heat in the tyres, then balance them. That's how I do it.

greg928GTS

When I brought the car in to have the tires balanced, it had been sitting for at least a week, and then just a few minutes drive to the shop. So maybe I do need to take it out for a longer run, drive really fast and get the tires warmed up, then have the tires balanced.

If someone else comes up with one more thing that could be the problem . . . .

Just kidding, I appreciate the suggestions, but just don't know how any of you find the time to keep up with these things.

Where does one get wheel rotors balanced?

Pfunde

Did you look at the wheel when it was balanced . Sometimes a wheel will come out as well balanced but not perferctly round. But when it rotating on the machine it's very easy to see. The rim could also be just a little flat. Reg. rotors, you're talking about brake rotors ? If so, they should be balanced. But here in Denmark there's a company that cuts/grind rotors still on the car, and also balance the wheels on the car !

danglerb

Try another shop. Ask around every town seems to have one place that does the few dollars more but no issues balancing.

Fortunately I haven't had a vibration issue in last two cars, so I don't pay much attention, but it used to be that some shops used a cone type thing to center the wheel, and some used the studs which is sometimes different centered.

Spinning a wheel on the car should reveal any balance issues if present. Last guy put a mark on the tire and used a spinner and a strobe light.

Does anybody have a accelerometer transducer that works with a laptop, would be fun maybe to do some vibration analysis.