black ice

Please help. I'm dying. My car has a speed related vibration that you can barely feel even going 5-10 mph and it gets worse as you go faster. You can feel it in the seat of your pants and it feels substantial between 40 and 80mph.

I have a 95 C2. Options are a factory short-shifter and LSD/ABD. My car has euro M030 springs all around a Bilstein HDs in back. The car was very low and poorly aligned, so my shop raised it back up (about an inch in back I think) so the front/rear relationship is correct. He could only get it between Euro standard and sport heights anyway.

The alignment had way too much toe and about 2.5 degrees camber each side. I drive a lot on freeway so he put it back exactly to stock specs. He did no kinematic toe, which should be done when ride height and camber are changed, so don't know if that would be a problem. But he double- and triple-checked settings.

Here is what I've done so far.
- had wheels/tires balanced twice, runout checked (I watched...)
-checked the play on rear bearings - they feel fine but with each rear wheel mounted and off ground , I am able to get discernible movement (although small) twisting side to side. Is there a spec for this and is it normal?
- checked axles. One outer boot torn.
Please let me know of anything else you think I might check.

Edit: also curious on your thoughts how bad my toe setting would have to be for that to be a factor in vibration.

thanks in advance, folks.

Dave

chris walrod

Have you checked the front lower control arm bushings? How many miles are on your car?

black ice

87K miles on the car. Did the rack about 9K ago and all seemed well up front - How do I check/isolate the control arm bushings as cause? The car tracks really nice and straight on freeway after alignment...

chris walrod

While this control arm is off the car, you can see the cracking. On the car, you can pry against it and the tub to show any cracking. Without prying, it will look normal. You are looking at the forward bushing on the front lower control arm.

Typical symptons include steering wheel shake, but not always at the same speed or frequency.

macanswer

Just my two cents but if you are feeling something at 5-10 mph it must be something significant that is bent. The first thing that occurs to me is maybe someone put a jack under a half shaft (axle) although it would be pretty hard to get a jack on those parts. Do you feel the vibe in the steering wheel or as a shudder throughout the car?

Recently, after putting new springs and shocks in my car the ride height and alignment was all out of whack as expected and I had a shudder in the car that I think was being caused by ride height and the rear swaybar being pre-loaded. Having the rideheight set and the car aligned solved the problem. Funny I just posted about how Bilstein HD's have the swaybar end link mounts as part of the spring perch. This means as you adjust ride height at the rear you pull the swaybar up and down. Not ideal. Make sure to check that your swaybar is not "jacked up". :-)

I'm still not convinced you could feel anything that would be caused by suspension mis-configuration at 5-10 mph though.

Marlon

WHEN did the 'shudder' problem arrive? All of a sudden or following a recent maintenance action??? If it happened immediately following your raise & align, it sounds like something went possibly arwy then. A bent or damaged halfshaft as mentioned above is about the only thing that rotates at a frequency (other than a really bad wheel or tire) that you would 'notice' at lo-speeds. A seat-of-the pants feel sort of indicates the problem to be in the back end anyway. You could check that by putting the car on a safe overhead lift and spin the rear wheels. You could also double check security and tightness of all fixings involved in the raise and align. You indicated that your wheels are all true and that your tires and undamaged. Might consider installing another set of wheels just to make sure it's not your wheels or a bad tire. IF you were local to me we could install any number of spare 993 wheel/tires sets that are cluttering my garage!

black ice

Had alignment and got tires pretty close together - seemed like it started getting worse after alignment. Good idea on wheels and tires, my friend is lending me a nice set of his to swap to eliminate wheels once and for all.

You mention the swaybar drop link mounts on the bilstein HDs - what a dumb design. Huge PITA to set ride height with that design. Shop I took it to is willing to check alignment and load on those parts again this weekend so hoping the problem presents itself.

Yes, definitely seat of the pants feel. One thing still bugging me (which I'd rather not fix if not broken due to cost) would be toe control arms but with wheels off of ground I can twist wheel side to side and get a -little- play (at least more than I've felt on other cars).

Garth S

Gently run your fingertips around the tires tread face: this will reveal any irregular wear patterns that can be difficult to see - and are often a vibration source, even on a freshly balanced tire.

TMc993

Vibration through the seat of the pants without a steering wheel vibration is a definite indication of the problem being in the rear.

As mentioned above, the fact that the vibration increases and decreases with speed indicates a problem with a rotating part, most likely a wheel or tire.

Is it possible that the out-of-spec alignment caused your tires to wear in an manner that caused no vibration in the out-of-spec mode, but sets up a vibration when the alignment was put right (Because the tires no longer have a uniform shape and are now rotating in a different manner)?

Also, I know you said the tire shop checked the tires, but I would re-check for the possibility of a belt separating on one of the rear tires. That is a problem that will present a minor vibration when the tire is cold and speeds are slow, but get worse (And more dangerous) as speeds increase and the tire heats up.

TMc

black ice

Thanks for the advice Terry, that makes me feel like I'm headed down the right path. I came to the same conclusion yesterday that I might have a bad tire. But hard to say that it would be from the alignment because they are brand new Bridgestone Potenza RE750s and am working on the assumption (however unlikely) that there is a manufacturer's defect. Ran my hand around the tread like you said and it feels fine, so I may take my wheels back to the balancing shop that has the fancy Hunter and have them "load force balance" the tire or whatever they call it - they put this big roller that presses down on the tire and it's able to tell if there is a stiff spot (even if tire is rouund). I definitely have an appt to meet a buddy with nice wheels and tires that will fit and I'll try his out to eliminate the problem. He's got 18" Rufs powdercoated a dark grey - they will look awesome on there, even if it's just for five minutes.

Do you think my 993NA can spin his Pilot Sport Cups??

I'll report back Saturday....

Dave

TMc993

Oops! I didn't realize the tires were new...Strike the part about the alignment causing unusual wear...Do let us know what you find this weekend.

TMc

DJF1

a long shot, but have you actually checked the wheels? If they are bent, for sure you will feel vibration... Had the same thing in the past on another car and the culprit was a rear wheel... and yeas it was "balanced" LOL

Peter B

When the new tyres were mounted, did the technician seriously over inflate them? I hope he did because I had a Merc 190 2.5 that suffered the same speed related vibration that defeated everyone (even Dunlop's own tech dept that took the wheels/tyres away for inspection). It turned out that the beading was not properly seated and the tyres were physically moving or squirming on the rims. The fact that it was a diesel with tons of torque did not help either (at least it had that in common with a 993!)

2ndof2

Unless I missed it nobody suggested looking at the sway bar drop links so try that and also spray out or drill out brake pad deposits from the rotor holes. Do all the above and the stuff I mentioned here and I bet you'll resolve the issue. Assuming you use the car frequently enough that the tires aren't temporarily flat spotted from non-use?