RKD in OKC

A questions...

Are you by any chance using any sort of aftermarket valve stem caps? Where the wheels/tire sets balanced with the valve stem caps on?

I had a boxster that I added those valve stem caps with emblems on them. Caused the same sort of vibration on the boxster, started at 80, smoothed out at 100+. Took them off, and vibration went away. Turned out tire shop balanced wheels/tires without valve stem caps. They weighed about an ounce.

IcemanG17

I like the dyno idea...... I can get you a great price on dyno time in west sac if needed..... Also the dyno at Thunderhill is only $60 for 3 pulls too.....

UKKid35

Why has no one mentioned brake discs?

Bill Ball

Wouldn't loose front wheel bearings be felt through the steering wheel? Anyway, yes, I did repack them and make sure they were snug very recently. There is no play in the front wheels.

Bill Ball

Valve stem caps weighing an ounce!? Wow. No, that isn't the issue. 3 sets of different wheels, one of which rode fine before, had no effect on the vibration. Thanks. Keep trying.

Bill Ball

I have looked at the rotors and they are in good shape and run true, turning them against a dial gauge. But, now that you mention it, let's say a rock got inside one. I might not see anything until I spin them at high speed. So, I will look look further at them. Again, I think it's the rear if anything since the vibration is not felt through the steering wheel, but per chance I am getting fooled, I will check them all tomorrow. Thanks!

brianrheffron

Probably not much help since you have tried three sets of wheels
but I had similar symptoms on my 89 S4. Fine up to about 60
then vibration/ wobble started to build up. I wasn't brave enough
to drive through it to see if it smoothed out at higher speeds.
Assumed it was a balance problem but the wheels balanced out fine.
It turned out that the wheels (18" Cup 11) were slightly oval probably due
to low section tyres not coping well with potholes. I had the wheels
trued and rebalanced and all was fine.

linderpat

This is what I would re-do. You have eliminated all of the low hanging fruit, and the problem seems precisely pointed to something you did before. Time to drop that tranny. If it isn't centered properly on the mounts, then the vibration could occur.

Tom in Austin

There is a procedure in the WSM to take up any difference in the trans mounts with shims. You loosen the bolts, lift the transmission slightly, measure the gap beneath each mount and then shim it equal from side to side.

Since you're looking for something in the back and just did the mounts should be an easy thing to check and eliminate as a possible problem.

Jerry Feather

You said that you "checked the wheel bearing," but I don't really know just how one could go about checking the rear wheel bearings. I think you are going to ultimately find that you ahve a rear wheel bearing going out. They are a real beefy two row ball bearing with one outer race and two inner races. They look like they could go just about right on a D-9 Cat. I think one row of the bearing can go out while the other is still carrying a lot of the load, which might be why you have had it go on so long without a complete failure of some kind.

When this happened to my S4 I could not drive 80 without the vibration, just like you describe, but I didn't try to see what the upper limit of the vibration was. When I took it apart I found that the axel nut was little more than finger tight and that one of the bearing inner races had hammered the hub to the point of very looseness inside that part of the bearing while the other inner race was still tight.

I suggest that you order two new rear wheel bearings and replace them both. The procedure is a little complicated, but with some tooling from Harbor Freight and a press you can get it done yourself.

That is my 2 cents worth.

Jerry Feather

Koenig-Specials 928

If its due to a rotating mass (wheel/tires/rotor, shaft) then the only way to check it is to have the wheels balanced on the car. There are a few shops that still do this. They lift the *** up, use a motor that is pushed against each wheel (while attached to the car) and spin it all the way up to 150 mph while checking for vibrations on the hiood, fenders, steering wheel. As vibrations occur, they move the balancing weights with a piece of tape until it is completely balanced. After that, it will drive very smooth on the road because it balances the rotors as well. Do it for each wheel. It is the only way to get a true balance. Luckily, there are two shops doing it where I live.

killav

Bill,

I know you have tried a few different sets of wheels and tires, but my car did this very same thing. Two DIFFERENT sets of rear tires did this to me. Both rear tire sets were used. I bought a brand new set of rear tires, and had them Road Force Balanced. Car was perfectly smooth after that.

Regarding the on car balance, you will have to hunt around because fewer and fewer shops still do this. It is expensive, but if you go that route, you will obvioulsy need to mark the wheel somehow in relation to the lugs to make sure it is installed back the exact same way if you take it off the hub.

If your due for tires, get some brand new ones and road force balance them. Also, if an enormous amount of weight is needed on one side of the wheel to get a good balance, ask them to break the bead and spin the tire 180 degrees around the wheel. That usually results in much less weight needed to balance the wheel. You will have to talk to the tech up front so that they don't charge you twice to balance the wheel.

That's my advice.

blown 87

find a shop that can do high speed on car balancing, at least then you will know if it is a tire/rotor issue.

My guess is that something is not lined up just right, as it started after you did mounts.

Randy V

Wow - you removed your supercharger?

How come?

BC

Its an automatic, so I do not see where you have done this -

Can you find out if it is gear dependant? 4 gears, top gear should be one rpm, and if you move it to 3, it would be another.

Any change?