TeufelHei

It's the only reasonable explanation for why it shakes so bad at 90+ MPH

I've checked the balance of the wheels (good) and repacked the front wheel bearings. The tie-rod ends were replaced with the steering rack.

There was a small ammount of play at the upper A-arm ball joint, is this likely the culprit? I suspect so, but is there a way to rebuild the joint without buying a new arm? Who's got the parts? What other sort of WYIAT things should I take care of?

Jim_H

Sure does sound like a balance problem. Could you have thrown a counterweight?

GlenL

Could be looseness in the joints and/or an alignment issue.

Quick Carl and Rennbay have jointly developed a kit for the upper A-arm balljoint. I think it's for the early (pre-S4) cars and is doable without removing the arm. I used a rennbay balljoint kit on my 944 and was satisfied. http://www.928motorsports.com/

Imo000

Yes, it's either a balance or a bent rim issue. You can have a wheel 100% balanced and bent at the same time. If the technician is not looking he'll not notice the rim being out of round. The machine will show that it’s 100% balanced but once it’s installed it will shake like hell.

Also it’s possible the mating surface is not true. Either corrosion built up or incorrect machining of the rotors can lead to wheel wobble.

I hope thishelps!

John V

Tim,

when I put brand new 18" tires and rims on my car, I noticed some vibrations that I didn't like. They weren't severe but, even though the package came high speed balanced, I still had vibrations that got worst with speed. Since the package was mail order, I took the car in to a local shop that had the "roadforce balancing system (sp ??)" and it made huge difference! It may be worth looking into - worth the inflated price in my view.

jyoon

Could the engine or tranny mounts cause this?

Mark

BTDT! My issue turned out to be a flat spotted tire - would balance PERFECTLY...and still shake like heck.

The "Road Force Balance" actually loads the tire with weight while running it up to speed. It not only indicates balance issues - but out of round problems. It is done on a Hunter GSP9700. My local shop that has one charges around $15 per tire for the balance - but that includes shaving if necessary to fix the out of round.

You can locate one here -> http://www.gsp9700.com/pub/search/findgsp9700.cfm

Ron_H

Have you checked the inner upper control arm bushings? Where the A-arm meets the body? Mine were worn and the car was aligned twice until Brian @ Devek walked up and took a close look at them and spotted the problem. Not an easy fix, but might need to be done.

The road force method sounds intriguing. More good stuff to learn from the Rennlist people. Thanks. I have had mysterious balance problems in the past and particularly in that range. The looks on people's faces when I tell them the speed at which the problems appears is interesting as well.

TeufelHei

I'll probably order a kit from Carl, since I know they are going bad. I'll have to do the poly uper bushings too. I guess I'll have to get the car aligned (again).

Any advice on the parts replacement scheme? I've got a donor car parked next to it if it's something that is a lot easier to do with the parts out already. Might not be a bad idea just to swap the known good arms over (and put new bushings in).

I'll look into the road force preloader hunter super deluxe (with cheese) machine in the area. Actually, I've got a "free" alignement coming my way since the car pulls right after having it aligned. Should I wait until the parts are swapped or what?

TeufelHei

Yeah...I feel kinda silly telling someone about a balance problem at 90+ MPH, but the car can (and has done) in excess of 140 MPH with narry a flinch. This really annoying, suspension wrecking, shudder notwithstanding.

If they didn't mean us to drive so fast, they would patrol I-10 a whole lot better. Especially in West Texas.

heinrich

tyres. have you tried clutching at speed? thinking ttube or clutch

cobalt

My car was very nervous above 90 mph until I changed the shocks. How are yours? I had a shimmy at 90 which all went away when I replaced the shocks with Bilsteins, corner balanced and aligned. The car also became much more stable with new tires as my front end was originally too low and they had worn unevenly.

Nicole

Is it the body or the steering wheel that's shaking? If it's the body, I would focus my search on the rear end of the car.

I once had a car where the rims were not exactly round. As a result, once the tires were on I was driving on egg-shaped wheels. They were able to balance them perfectly, but there was vibration still. So they put ot in a grinder that grinded the tire to be exactly round, despite the non-round rim. That worked reasonably well. But that car was not nearly as powerful and fast as your 928.

I also would look at the bolts for the CVs - one of the CVs fell off on my car, because its bolts had not been tightened and torqued properly.

Tom. M

Chris Ford recently had an annoying vibration at speed (think around 80 or 90) which he first thought was an engine miss...

Ended up being the torque tube ..as the front bearing migrated back leaving the front part of the shaft unsupported and causing the vibration.
May want to look there...

good luck
Tom
89GT

TeufelHei

I just changed the TT and clutch, no problems there, it is definitely speed dependant.

I just had shocks and springs (Bilstein/Eibach) installed and the problem persists.

It's better than it was, it used to feed back a lot into the steering wheel. Now, not as much but it still shimmys.

Normally I would think it's tires and just go about solving it that way. Except that I have swapped the tires in all possible combinations without positive results. I've got the feeling it's front suspension related.