porsche_addict

I have a shimmy that is felt in the steering wheel from about 50 mph onwards on my '86 951. The tires have already been balanced twice since I installed new tires last year, but the shimmy continues. Is it possible that the balance has not been done correctly? It seems to get better once the car has been driven about 10-15 miles. I don't see a tire that looks out of the ordinary and the tire pressures have all been set. What suspension items would most likely cause a shimmy?

drift a 944

Tie rod ends or control arm ball joints most likely. With the car jacked up, try grabbing a front wheel with two hands and shaking it left to right and up and down. If you feel like there is any play then you should inspect these parts carefully to see if they look worn, blown out or loose.

But as a last resort hope, do you have another pair of front wheels you could try swapping onto your car to see if anything changes?

porsche_addict

I had a service record from the P.O. that indicated that the front ball joints should be replaced. I had them inspected by a few shops and none of them could get the front wheels to move with the car jacked up. Is there a specific way to test for worn balljoints? I was thinking that maybe a wheel is bent and untrue? What is the easiest way to check for a bent rim?

drift a 944

At our shop we wiggle the wheel in all directions to see if there is any play. To check for a bent rim can be tricky... visually you can spin the wheel and inspect it for flat spots or lumps... but to really get an accurate reading you have to use some sort of feeler gauge... I have only seen a wheel repair specialist dude use one, and he can put it on different parts of the rim while spinning the rim to see if there is any slight flat spots.

Fluidplay

Had the same feeling at about the same speed. Had just replaced steering rack, inner & outer tie-rods so I know it wasn't them.

Take the front wheels at 6 and 12 o'clock and rock back and forth.. If you feel a clunk as you're doing it, it's probably the joints. You can also wedge a pry bar between the arm and steering knuckle. Pry up if there's any play replace.

Check out my post "Control arm failure" for pics of the carnage.

supes6

Most likely a bent rim, or ****ty balance. I have one rim that a shop told me was bent, and it loses air quicker than the others.

porsche_addict

I'm going to get another tire balance at a good tire shop. I will also check out the rims to see if I can spot anything out of order. By the way, some older service records indicated that the the caster blocks were getting to the point of needing to be replaced. What role does the caster block play and how can they be inspected?

John_AZ

"Shimmy" has been covered a few times.
Back in 1995 when the internet was mainly text only it was covered in section 5.4.11
http://69.55.175.34/porsche/944faq.txt

On the wheel balance is all but gone.

Your brake rotors could also be out of round-warped.

When you test the wheel for "play" at the 12 & 6 oclock position, a slight amount of play is from the front wheel bearings. Just a small, tiny amount so the bearings are not adjusted "over tight"

Some have had success with putting the locking lug nut opposite the tire valve to compensate for the gram or 2 of the tire valve.

GL
John

dinodanny

If I remember correctly when you mount your wheels the valve stem should be at the lug that is opposite the 2 screws that hold the rotor on. If you you use the locking lug nut it should be opposite the valve stem. I've had some success in diminishing the shimmy with this mounting method. The position of the locking lug does make a difference.

awilson40

I had the same issue and could not see any play by wiggling wheel or tire rods.
Then I jacked up the car and used a large screw driver and started prying on the ball joints and BAM.... the left side could be moved while the right side was firm. Replaced the left Lower control arm and problem fixed.

944Ross

Had the identical issue at same speed. Added about 1/8 turn of the tie rod towards toe-out and it went away. It appeared to keep the tie rods under tension, taking up whatever little slack there was at speed. No effect on handling, steering wheel position or tire wear.

Lizard944

John is on to something here. Back in "the day," Iceshark, Hans, and I did some experimenting to try to get to the bottom of the infamous wobble. One common factor was the use of locking lugs which were significantly heavier than the stock lugs. When the lock lugs were positioned near the tire valve stems, the combined weight was enough to induce a hefty wobble. This was even more dramatic if the front wheel bearings were even slightly loose. Solution was to chuck the locking lugs and run all five stock lugs, or place the lock lug on the opposite side of the tire valve stem which creates a counter-balancing effect. Check your front bearings by the recommended procedure: Just tight enough to be able to push the outer bearing washer around with a screwdriver. Don't rest the screwdriver on the hub to give you more leverage while pushing on the washer. I then give the bearing clamp nut an additional ~ 1/16th of a turn. Then make sure the wheels spin freely.
--Lizard

porsche_addict

I will check into the security lug nut and see if that makes a difference. There is a bit of play in the front wheels but I believe that this is only for proper tightness for the wheel bearings.