speed12sil

Now, I have used the search button and the only matches that came up from the 993 sub-forum dealt only with steering wheel vibration whilst braking, and my situation is different...

I was driving the 993 yesterday and when the car was going faster than 60 mph, around 75-85 mph, the steering wheel was vibrating quite a bit. Now I was able to hold it and it still steered fine, and I don't think I felt any vibration coming directly from the tires when I held it somewhat firmly. The vibration seemed to decrease in magnitude as the speed dropped and I think it stopped as I dropped below 50 mph. At city speed (~37mph, or 60km/h ) I don't get the vibration at all.

Interestingly, the sunday the week before I drove at about the same elevated speed(~80 mph), and the steering wheel was not vibrating. It sat in the garage since then and only got driven again yesterday.

I got this '97 993 about a month ago, and checking all of the receipts(dealer/Weissach) from the previous owner(there were two before me), there were no service memo related to front suspensions/steering mechanism, nor tires. Last service was done back in April and was not driven much after that (less than 500km if I'm not mistaken). The front tires were *probably* changed by the 2nd owner at a private shop as I did not get any receipt for the two front tires. Wheels are still the original optional 18", so I'd assume tires/wheels not balanced is probably not the cause. As long as the tires are mounted correctly, there's no need to re-balance the tire/wheel right?

Tire pressure measured yesterday was 36 fronts and ~41 rears. This was done approx. 6 hours after being driven, parked in the garage(temperature was pretty cool, at most 23 C), so pressure should be that of cold...

So....after reading such a long post, could anyone please enlighten me as to why my car is doing this?

Thanks a lot for the feedback

993inNC

sounds like a flat spot from sitting that long. If they are a soft compound, its easy to retain that flat area, should work itself out with enough use. Happens to me from time to time.

epj993

To start, I'd suggest trying two inexpensive things:

1. Remove the front wheels and flush the brake rotors with a jet of water. Brake dust can accumulate inside the vanes and the drilled holes. Use a small drill bit to clean out the holes.

2. Have the front wheels rebalanced. It's possible you lost a weight.

I had a slight shimmy that only appeared at 55-60mph. I cleaned the rotors and it eliminated about 50% of it. I then had the front wheels rebalanced and that completely eliminated the vibration.

If these don't resolve the problem, I'd have the tie rods checked to see if they're worn.

p_carfan

Most Likely Culprit ....Use a quality tire balancer such as a "Hunter"

TCallas

I would recommend you check things in this order. First off, it is not impossible that your front tires are flat spotted if your car sits whitout being driven for any length of time. Second off, a good front wheel balance should fix it if you have lost a wheel balance weight or just have a tire/s or wheel/s out of balance. Third off there is a common problem with the 993 front control arm bushings cracking when they age but these bushing cracks are fairy difficult to see without being trained for what to look for. In the early stages of failure, the control arm bushings have quite a strange fault feel (Steering wheel shimmy). When they first start to crack, they act like a surface activated (intermittent) wheel balance problem but as they get worse the problem is mostly between the 45-65 MPH range and all the tire balancing in the world won't get rid of that annoying steering wheel shake or shimmy. Now, having said all that, there are basic items I have left out considering the following is OK, I.E. your brake rotors, wheel bearings, tie rods, steering rack, all balljoints, shocks and front suspension components are OK, your lug nuts all are the same weight (same type), etc...

geolab

I totally agree. As per porsche workshop manual, the anti-theft nut should be mounted opposite the tire valve also.

From past experience, vibratons at 70mph are usually solved thru a good wheel balance.
Vibrations at 110mph are allignment problems.

__________________________________________

'97 Carrera S 100% original

pcar964

Try this little trick - drive at 70mph or so, see what the wheel feels like. Then lightly tap the brake pedal, and see if the vibration changes/gets worse. Then you'll know if it's warped rotors or not.

speed12sil

Thank you guys so much for the valuable inputs. I'll have to go try those things asap.

Francisco Martinez

I know this is an old thread but did you ever get the vibration issue resolved. I have a similar problem on my '95 993 and have done the following without fixing the problem:

New rear rotors and break pads (Not that I think this has anything to do with the problem)
Rebalanced all 4 wheels/tires
Tried my recently balanced Track wheels/tires (With brand new Nitto-NT01s)
Properly torqued the Lug nuts and placed the anti-theft nut opposite to the valve stem.
Replaced Front arms's rear and front bushings with Powerflex replacement units.
Cleaned the Rotors with 1200psi pressure washer
Installed Steering Rack Brace
Testet calipers to assure no caliper stuck problem (No vibration change under braking anyways)

There is no wheel bearing noise at any speed. What should I try next???? Replace the Tie rods???? I am running out of options. My mechanic insists it's wheel balance but this cannot be, I have tried two recently balanced sets plus the vibration is not constant as expected with a unbalanced wheel. I realize that under acceleration I may not exprience the vibration. Also the vibration starting point may vary from 55 to up to 70 mph.

This is a little frustrating, any suggestions appreciated..

grmnxtc

The other thing (and about the only thing) I recall from the Tony Callas 993 day...

Front suspension A arm bushings... on early cars these can be very worn and result in all sorst of "strange" vibrations, floatyness and assorted maladies..

Get your wrench (or yourself) to see if there's any play in them . IIRC this ivolved a big crowbar "flexing" the A-Arm when it was up on a lift.

JChiles

I had a slight vibration at those speeds, a new wheel balance cured maybe 50% of it, which I was fine with since it then was very slight.

Recently I fitted a new suspension and it is completely gone as far as I can see now. Components changed were shocks, springs and sways so I can't really be specific, but it clearly can be suspension related as well. Of course an alignment was done after the susp change, but the alignment was fine before as well.

pcar964

Can the control arm bushings be replaced without replacing the entire control arm? I ask, because the arms are expen$ive and I don't see a separate listing for just the bushings (on Pelican, at least).

Terry Adams

I replaced my A arms at 75K when I did the suspension upgrade. The bushings were cracked and had about 1/4" play. At the time, there were no bushings sold separately, but I think later some outfit in the UK sold a polysomething bushing separately. I can't recall the thread, but a couple of people commented that they were expensive and difficult to insert.

95 C4 993

I had the same issue when slowing down at about 40mph last year and the vibration would start. It was on deceleration for me. When I replaced my rotors and pads, everything was fine.

gonzilla

Powerflex is the name of the company that makes the bushings.
http://www.powerflex.co.uk/products....5&catalog=0125
They are available in the states through this site:
http://powerflexusa.com/
No affiliation. Just information.

I haven't used these, but plan to at least try them rather than buying new control arms when the time comes.