Mystery Steering Wheel Shimmy- Help Needed 2003 C4S

Got a mystery steering wheel shimmy that I need some help diagnosing since my dealer seems to be a bit helpless... Don't know when it started as I had a weird ownership start to the car with not being able to drive it too far(highway) due to a back surgery. Once I did get it on the road, definitely a steering wheel shimmy that comes on 65+. Tried wheel combinations of spacers/no spacers, different tire pressures and no change. Car has new lower control arms as well. No issue with steering wheel shimmy when brake is applied and brake application actually seems to stop the shimmy if I am traveling at highway speeds. The shimmy is intermittent/not always consistent and i really only felt in the steering wheel. Car is a 2003 996 C4S. Here is what we have done so far: Wheel balancing- Dealer said the fronts balanced out, but rears still had high road force. Shimmy persisted New Inner and outer Tie rods Shimmy persisted and maybe made it worse I tried another set of wheels on the car- Not fixed, but dealer said the front wheels had high road force So, I am just torn on what to try next, dealer thinks throwing 4 new tires at the car would fix the problem, but I don't trust that is the issue with varying wheel sets not changing the issue. Unless someone can tell me with certainty that the rears being out of balance/high road force would cause a steering wheel shimmy. Any thoughts/help appreciated.

Quotes source post: 18886184

There�s a dude that has a similar issue that ended up being a bad shock.

Wheel bearing. Putting on the brake stabililizes a wobbly bearing.

A vibration transmitted through the steering wheel is caused by the front suspension. Vibration felt at the driver seat base is in relation to rear suspension vibration. Are your front rotors warped? If you�re awd, it could be a bad axel shaft. But you did say it�s intermittent.

You (the dealer) haven't mentioned in what direction the wheels had high wheel force but I presume to the side (and not vertical althoughthat is the direction typically measured on wheel balancing equipment) but since both front wheel sets tested had it, it doesn't exclude them being the cause for your C4S's shimmy. In any case you want to put on a set of wheels that have little to no wheel side force as well as little vertical wheel force in order to check whether that is the cause. I second the suggestions of bearing and shock absorber. Edit2: Front rotors are fine obviously as no shimmy present when brakes are applied. Axle shaft out-of-balance is a possibility, however I've never seen a balance weight spot welded onto them which suggests that they don't require it.

Never trust the wheel balancer person. Try another balancer. The wheels need to be carefully balanced in 2 planes and they need to be round

Quotes source posts: 18886779, 18886247, 18887197

Any tests that I can to do rule this in or out? Any tests that I can to do rule this in or out? I have tried two different shops for balancing one set...I may be at that point though to try a third if I can rule out the other two above as possibilities.

Quotes source post: 18886184

Andy, sounds like it's a new car for you from your description. The definition of shimmy may vary so here is a question for you, is it a vibration shimmy (wheel out of balance) or is it a light feeling on the front end at higher speeds shimmy? Any idea how much camber you have in the front end? The reason I ask is that if you are new to the 996, they do have an alive feeling in the steering which is amplified at higher speeds especially if you have a bit more negative camber dialed in on the front. It causes the front end to feel like it is following every nook and cranny on the highway. Mis-alignment can create odd behavior up front as well. Just something to think about. Not a diagnosis.

One new update... took the car for a drive to try and diagnose some of this. While driving with the windows down, when near a curb/wall i could hear a rhythmic tsh,tsh,tsh,tsh sound. It was speed dependent. Assuming this leads me to think more like the wheel bearing is the culprit...

Rule of thumb, if vibration starts at under <25mph in steering wheel or seat, its a bent wheel. over > 25mph vibration in steering or in seat, is a out of round tire/bad tire belt, or out of balance good tire. Bring it to a truck shop that does on the car balance. They can spin it up on the car and you can pinpoint what wheel/tire is the culprit. You say the wheels were changed..? did you change the tires also, or use the same tires on the same corners just on different wheels..?

I had a similar problem on my 99 Carrera. Wheel balance was the primary cause but the shocks were dead as well. Balancing the wheels solved most of the vibration but the front shocks (struts) were dead by this point (150k+ miles) so the wheels were dancincing at freeway speed. Now that the tires are balanced and the shocks are new the car drives great.

Sorry if this is the naive suggestion, but have you jacked up the car and felt for play in the wheels or other bits of loose suspension? It's usually the first suggestion for a suspected wheel bearing, so I probably just missed it. With hands at 3 and 9 if the wheel will shake a little, it's a suspected tie rod. With hands at 6-12, it's a wheel bearing. I'm not a mechanic, I'm just repeating what I've heard others say. I'm sure someone with more expertise can elaborate. EDIT: And my status as a naive idiot is confirmed. See post below by theprf.

Quotes source post: 18890315

You'll never feel play in these wheel bearings that way. If it moves at 6-12 it's a lower ball joint. At 3 and 9 could be a tie rod or the diagonal arm. The only useful way to check through bolted ball bearing type wheel bearings is to (1) loosen the axle nut, (2) remove brake pads, (3) then check for smoothness and/or play. The really high torque on the axle nut holds everything together. Or let me put it this way, by the time it's possible to feel play in a fully installed wheel bearing like this it will be obvious because the wheel will have extra negative camber - because the bearing is totally worn out. A less intrusive and almost as good way to check is to drive in a parking lot. It helps to have an observer outside the car. Drive in figure 8's at a moderate speed. If the noise is different depending on which way the car is turning it's probably the outside wheel bearing. The do the same thing while riding the brake slightly. The brake stabilizes the wheel bearing so if the sound changes, it's probably a wheel bearing. If the sound doesn't change then I'd be looking at outer CV joints or something else further back in the drivetrain.

Since its a C4S, A tired CV joint in the front end will also give some weird feel in the wheel often quite a while before the CV is really totally done..

No where in any of this has an alignment been mentioned. Has a four wheel alignment been done? Normally checked after tie rods are replaced.

Yea and not of a basic machine it needs to be a 4 wheel thrust alignment.. I'm lucky to have a local shop that is right by a race track and does a ton of alignments for track cars, and also does rally cars as part of their business. They have a very nice alignment rack and he knows how to use it.. If your in the Portland Oregon area, A-N-T Tire.. (Shameless plug for a friend... )

What pdxmotorhead said!