mkd944

I need some help to diagnose a problem that I am having. When my car reaches 50 mph the steering wheel shakes violently. As I get over 55, the shake starts to dissipate and above 60 mph it is barely noticable. Same thing under 50 mph. I have searched for threads on this topic but have not found anything that matches my problem. Most talk about brake issues and I do not believe that it has anything to do with the brakes. I have jacked up the car and pulled on front wheels from the 12 o'clock and 6 o'clock positions and the 3 and 9 positions and feel no extra play. I have been told that it could be the ball joints. I searched for those threads too and didn't get much info that I could use.

Has anybody else experienced this? And if so, what was the fix? It is really taking the enjoyment out of my driving.

Thanks,
Mike

sundog

Well, that is indicative of your car hitting a resonance in the suspension/steering assembly. The forces happening during this are amplified very much, and could do severe damage to the car. It could be as little as an out of balance tire/wheel or bad strut, but could be much worse. If you aren't a confident do-it-yourselfer, then take it to the local indy ASAP.

Jacke2c

Have you had the balance checked on your tires (dynamic)? Have you broke an inner belt? Can you see a slight bulge on the tire(s)? Tire balance can make tires only vibrate at specific speeds. I would check that out once I have exhausted the obvious (struts (yes, worn struts can contribute to strange vibrations) bearings, CV joints, bent axle shafts, bent rim, all of which can cause the same symptom at a determinate speed...sometimes even by differing harmonics of difference in balance between wheels on the same axle.)

I have actually witnessed out-of-round tires that were balanced, but would beat you silly at certain speeds and then ride normal at other speeds.

mkd944

Thanks sundog. I am not afraid to do-it-myself. Just not sure where to start. I was just over on Pelican and found an article on tie-rod replacement that seems to be the closest match to my symptoms that I have found online so far.

mkd944

Not something I had considered. My tires aren't new but there are no obvious signs of damage to tires or wheels. I will check to see if there are any obvious signs that I may have lost any wheel weights.

Thanks for replying,
Mike

Laguna Seca

Have your balance checked where they actually load the wheel with the same weight that the wheel would be stressed with while on the car. This will give you the most precise balance. I had this done on my '94 964 after I purchased it and it took care of the shimmy. Two of the wheels were way off! The cost was $80.00 here on the west coast. Good luck!

Makmov

With the front off the ground turn the wheel to lock one way or the other and check play at ball joint. Sometimes with the wheels pointed stright there is too much tension on the joint to feel any static play.

It can also be a symptom of a stuck caliper, but that is very uncommon.

Steve Weiner-Rennsport Systems

Hi Mike,

This one is plenty common and in the vast majority of cases, its due to a tire problem:

1) Balance
2) Out of round
3) Separated plies

There is FAR more to this and I'd be happy to discuss if you call me.

Naturally, I'm assuming that the wheel bearings are perfectly adjusted and there are no other resident issues with the tie-rods or ball joints.

John Boggiano

Mine just started doing this at 50mph too.

I am certainly expecting it to be a tyre/balance problem.

Frank 993 C4S

I had the exact same problem. Turns out that one of my wheel balancing weights fell off.

FeralComprehension

I had a similar issue recently and it WAS a brake problem; the stainless 'spring plates' upon which the pads slide get mung (that's a technical term) underneath them and the pads cannot retract properly.

One way to check for this without dissassembly is to drive for a bit with no heavy braking (and if possible, coast to a stop) and then check for heat in your rims/calipers. On my car there was quite an obvious temperature difference between driver (warm) and passenger (ambient) so it was clear I had some stuck brakes.

$0.02
FC

CabrioArtie

I had this issue too. It ultimately worked out to be lower control arm bushings. I spent a tremendous amount of time ensuring the wheels were true, balancing was correct and no tire issues. I was at my wits end when I read about the bushings on the 993 board and the description is exactly as you described it.

I had them replaced and all is perfect since. It would seem the rubber bushings deteriorate with age and can’t be easily diagnosed.

mkd944

Thanks to all for responding. You have given me lots to check out... which I will do this weekend. Feel free to keep responding as it sounds like others have experienced something similar and maybe your answers can help others as well. I'll let you know what I discover for my particular situation. RL'ers are great!

Babalouie

Just in case...check tyre pressures.

When they are really low, they can make you think that all kinds of suspension pieces are about to fall off

mgianzero

Mike,

Sundog had a very good point when he said "that is indicative of your car hitting a resonance in the suspension/steering assembly." The 993 has full rubber control arm bushings which degrade and weaken with age (and miles.) When you reach a particular speed, the suspension responds to a particular shake in your car, but often times goes away at other speeds. Take your car to an alignment or suspension shop and have them put the front wheels in the air and apply some lateral pressure with a pry bar to the control arms. If you see excessive play and/or rubber separation, you should replace your bushings. I installed the urethane ones and the car steers tighter and smoother than it ever did before.

Other peoples suggestions are all valid (wheel balance, flat spots on tires, etc.) but this is a quick check and any of these 993's at this age and over 60K miles can experience this problem.

Here's a video on how to check for the lateral play in these bushings. The part that examines the control arm bushings starts at around 4:40.

Marc