Anyone had a shimmy that was NOT the wheels/tires? (long)

I've been trying to track down a shimmy w/my car for a year now. I've tried a new set of Porsche wheels (5 spokes vs the SDs that came on the car), and recently dumped $1k into new tires to try and kill this once and for all. Shimmy="side-to-side" vibration at 55-65mph on certain roads. You feel it in your seatback, and in your legs, not in the steering wheel. It's been to the dealer a couple times to address. The first time, they "checked everything, and it was tight", rebalanced the Carrera 5-spokes & Michelins, and mounted/balanced a set of Winter-sports on my SDs. They were considering warranteeing the tires, but after they sat in the shop for a week, they said they checked them again, and they fixed themselves (flatspot) Net: the shimmy was worse with the lighter 5-spokes. Now, I thought the Michelins might have been "tweaked" when mounted from the SDs to the 5-spokes, so I'd rationalized that it must be the tires. Oh, but to throw a monkey wrench into it, the winter tires shimmied on the SDs, but at about 50% the "volume" of the 5-spokes. I brought it to a great local alignment/tire shop (Fordahl, for the locals) to check the alignment and rebalance the rears (they have a road-force balancer). Net: they were able to balance the rears, but noted a slight bend in one of the rear 5-spokes. Net: no change in the shimmy (still on the 5-spokes). Thinking that it must be the tires, or a combination of the tires and the bent Carrera wheel, I thought I'd buy a new set of tires (S02a's) and mount them on the original wheels (SDs). The dealer got a new hunter road-force balancer, so I was hopeful. They said that the wheels balanced perfectly, and were straight. Now, today, driving around extensively for the first time since the new tires were mounted (about a week ago), the shimmy appears to still be there (although less than with the Carreras). Random note: the shimmy appeared to get worse after taking a LH onramp fairly hard. Net: I may appear a little slow , but it's seeming like it's not the wheels/tires. So, here's what I know: - the shimmy is worse with lighter wheels/tires. - all bolts relating to the suspension appear to be tight (I put a wrench on anything I could grab) - no shake through the brake pedal, so I doubt it's the brakes... Anybody heard of a similar situation? It frustrates me any time I finally get a chance to put some miles on the car. Thanks for any pointers, Scott.

It's your alignment if you noted it based on a turning deal- I bet your toe is out-

I had a very similar problem on a 2000 Boxster S. It had only 8500 miles on it, but it turned out to be a front wheel bearing.

I've had my alignment checked and set by a very reputable local shop. The vibratration wasn't while turning, rather the symptoms seemed worse *after* the spirited turn. Heating up the wheel bearings, maybe?

Pete, how was the wheel bearing identified?

I would second the wheel bearing except for two things. One, it's very easy to diagnose so I would hope that someone would have found it by now and two, it should have gotten worse over the course of a year. Unless you don't drive much I guess. By any chance is your brake pedal a little soft on your first touch after one of those spirited LH turns? To check your wheel bearing, jack up your car and check each axle for play. Also, turn each wheel and listen for slight clicking or popping. Good luck, Jim

Basically, I went through the same things that you've done to try to cure it (changed wheels, changed tires, balanced and aligned several times). I also noticed an odd moaning sound when making a turn. All that added up to "must be a wheel bearing". Barrier Porsche was kind enough to order and replace both front bearings "just to make sure" even though it was not 100% certain that this was the problem. Apparently, there is no simple diagnosis because the wheels won't wobble even when the bearings are shot on the 986/996; you have to remove them to diagnose them properly.

Jim, I jacked up each corner tonight to test the wheel bearings (yes, had the e-brake off), and could sense zero play. Also, the typical noise that I associate w/wheel bearings going bad is absent. Re: brakes, that's interesting. I've noticed a softer pedal in general lately, but hadn't thought it could be related. What are you thinking? finally, the shimmy seems to come and go. It seems to be most prevalent at the end of a longer drive, and tougher to repro when the car is cold. I'm baffled at the moment, and not sure how much hell to raise at the dealer when at this point the behavoir is pretty subtle. Perhaps I just need some medication Oh, the car has 8800miles on it now. I too would think wheel bearings would get noticeably worse during this time.

If it's quite subtle then it may be somewhat normal. Is this your first 911? I've found that at least the 986/996 cars, especially with a sport suspension, can be quite sensitive to whatever factors cause some shimmy. Basically, they seem to shimmy naturally a bit more than other cars that I've owned. Note that the dealer's mechanic told me that on the new Porsches you cannot detect a bad bearing by wiggling the wheel when jacked up. But mine definitely made some relatively quite noise when making right turns over 40MPH which was suspicious enough to warrant ordering new bearings. If you haven't noticed, I live in your neck of the woods (I'm on Union Hill) so if you want a second opinion, I'd be happy to ride along with you and confuse you even more

Pete, I could use a second opinion. Plus, I'd love to see the 40ae. My wife, although she's definitely felt it at its worst, thinks I'm losing my mind I'm one hill south of you, at the north end of the plateau. Maybe we can find some time to compare rides next weekend? Any other thoughts from other folks would be appreciated. Thanks, Scott. [email removed]

The reason I asked about the brakes is that when my front bearing went the wheel would move enough through a hard corner that it pushed the pads back a very small amount leaving the pedal soft for the first pump afterwards. I could detect the failure by wiggling the wheel but mine was pretty bad. Good luck, jim

Update: the situation seems to come and go, and is most easily repro'able after some hard cornering, especially if it includes some hard left-handers. Hopped in my car after work a couple days ago, and it shook on the way home. Drove it in the next day -- smooth. The local dealer is stumped. I've written a doc summarizing everything that's been tried to address this, and am pursuing more aggressive action. We'll see.