wheel shimmy

[930slant]

I have an 88 930 that has developed a shimmy in the steering wheel that intermittently occurs above 60 mph even after I had the wheels balanced (on the car by Radial Tire, a very reputable shop in MD). Assuming that there may be a problem with front suspension components, can anyone recommend a Porsche shop in the MD, VA, DC area that specializes in suspension/front end work. Thanks!

[kstylianos]

There are many shops in the NoVA area that specialize in P-car work. But I don't know of any personally that are known for their suspension greatness.

Check out the PCA's Potomac region BBS:

http://www.pcapotomac.org/cgi-bin/ultimatebb.cgi

[Kevin Stewart]

Hi I think I would take the tires back and have them rebalanced, if there is any cupping or uneven wear the tires will shake, also if there is any debri on the hubs, the front wheels of a 911 a very sensitive, I would ask to see the tire run on the balancer, look at the very bottom edge(the balancer cover will only allow you to see the botton) if the tire moves any you have found your problem, the problem will increase with the size of the wheel, less sidewall less cushion. the tires can move side ways or up and down either way there will be a problem, also ask how fast there balancer is rated, most are only like 60, so I think I would find someone that works with performance wheels and tires more, maybe a discount tire, dont let them tell you different if the tire moves one the wheels, sometimes they can rotate the tire 180 degrees to take care of this, matching the high spot of the wheel with the low spot of the tire, (the little dots on the side of the tire), Kevin

[NoLift911]

I am assuming you have fuchs correct? I have found these wheels notoriously tough to throughly balance for all speeds with no detectable shimmy...you usually sacrifice a slight shimmy here or there. The wheels are so light usually the tire assembly takes control of the wheel.

First off, make sure they are not static balanced...all weights on the inside to hide them. This is ridiculous IMO that people sacrifice looks for imbalanced wheels/tires. You don't want this.

I am a wheel balance freak. I have found that the taller the sidewall of the tire the tougher it is to get a good balance. My fuchs on my 84 Carrera never really balanced up correctly. Moving to a 17's eliminates any balance problems since the sidewall is so small...no flexing at speed to throw the works off. Smooth as silk at all speeds.

High spots on the tire will not cause a shimmy...more of a hopping action which at speed just feels like a vibration. I am sure your suspension is fine...can't think of too many suspension realted issues to cause a shimmy except for the obvious...tug on things shake things, if it is really loose that may cause it, but probably just the tires, maybe a loose wheel bearing.

Some shops like Radial Tire can balance on the car as an assemby, you just need to index the wheels and put back if replaced, otherwise you have not felt anything like this type of vibration I had them do this with my fuchs and was not impressed, the tech was in a hurry and did not take his time. It takes a long time to get this right.

I used to balance the wheels on my Honda CRX in college. No shop could ever get it right. Front drivers are great for this...just put it up on blocks and run it up to your problem area and start moving weight around and experiment with different sizes. You can really fine tune this and you would be surprised at how much wheel weight you do not really need to make a wheel run smoothly. I was doing this to within .005 grams of weight

Tire balancing is somewhat of an art form IMO for correctly balancing a wheel. 9 out of 10 tires jockies just read the machine and do what it tells them without using common sense. Also if tire jocky 1 has just balanced some SUV wheels that are 30 inch in diameter and weigh 50lbs. the machine should be recalibrated before the delicate fuchs are balanced.

I have a ton more info on this if you need it.

-Jeff Kramer
nolift911@hotmail.com

[Kevin Stewart]

nolift911 a lot of great points that i didnt have time to clearify earlier but as the over all diameter of the tire increases even though the wheel gets bigger balancing does become an issue, 19 x10 per say most machines will not handle this wheel, my personal 18's we balanced 3-4 times, as the side wall decreases there is less give which leads to vibration if the tire is not true, you do find the the less the sidewall the treu'er the tire will be, but when it is even a little oor (out of round) it is almost impossible to get the vibration out, as with a larger side wall the tires may not be as true but will be sometimes be more forgiving, most times when we have a repeat vibration problem its is not so much from the tire oor but has movement side to side, a lot of people will put to wide of a tire on the 16x6 wheel which causes problems, Lot of great points you brought up and, yea, most tire jockeys dont have a clue, i have heard that would work well on my moms caddy, (235/75/15) of coures soft suspension etc, and have even made the guys rebalance because of counter balancing, but i think we agree that any movement of a tire side to side or up and down will casue problems for any stiff suspension car, especialy the 911's with out power steering, Kevin

[930slant]

Thanks for the information. The wheels are Racing Dynamics, 5 star design, 8 1/2 X 17 front and 9 1/2 X 17 rear. The tires, Toyo Proxes T1-S, have less than 1000 miles on them. (Prior to this, the car had Yokos that also had the intermittent shimmy, although not as much as the Toyos. i like the Toyos much better - they are much quieter, have better grip in the rain, and don't tend to follow ruts in the road.) Fronts are 235/45/17 and the rears are 265/40/17. The strange thing is that the shimmy is not consistent. For a mile or so it will be as smoioth as silk and the next mile the steering wheel will shimmy, sometimes rather slightly and other times very noticeable. i have also noticed that the steering wheel seems to shimmy (sometimes) when i am turning to the right or left at speeds above 60.

i will, for sure go back to the tire shop to make sure the tires are not our of round.

Thanks again.

[pnzr911]

How are your rotors? Front rotors take most of the load. They usually wear faster and can warp. I have a wheel shimmy as well on my 83. I balanced my tires and it helped but still shimmy. So I checked out my brakes/rotors/suspension. Guess what? My shimmy is caused by a stuck front left inside caliper piston. Thats right, the PO never changed the brake fluid. As we all know brake fluid attrackes moisture. This means eventual rust. My caliper piston was "fronzen" and was always applying force to the inside of the rotor. With heat and time this caused a slight warp. Be sure to check your caliper pistons and rotor runout before you drive yourself crazy on tires/wheels suspension.


Good luck!

[Kevin Stewart]

Is the steering wheel loose, do you hav the turbo tie rods, my car shimmies some and i was told that the turbo tie will cure it, Kevin