2001 Steering Shimmy/Vibration

[tfeld]

I did a search on this, but only two posts come up, mostly pointing to bad tires which I don't think is the problem here since they're not very old and don't have any signs of a problem.

What happens is that when the car is going at about 60mph or so, the steering wheel will feel a back and forth vibration/shimmy--sometimes mild and other time serious. At lower speeds I don't get this, and I don't always get it at all (even at ~60mph). I've thought for a while it might be related to the road surface, but I think it's getting worse.

I had an alignment done a few months ago and the car is in perfect alignment. Rotors and pads are also checked and not warped/warn.

I plan to take it to the dealer if I can't figure this out, but would prefer to have an idea of what is wrong before they tell me to replace everything under the sun...

[denisond3]

The vibration is due to some imbalance or out of roundness. It could be a tire that has some broken cords in it, or a wheel that has gotten bent, or a bent hub, due to a pot hole. I have had it when I got a tire mounted that wasnt fully seated on the wheel. I had a tire whose tread was delaminating from the carcass - which caused a shimmy.
If its a wheel or tire, you might try swapping it front-to-rear, doing one side at a time. The shimmy should move with the tire/wheel. You might still feel it, but it would not be shaking the steering, just the rear suspension.
A tire can go bad after hitting a pot-hole, and the imbalance (due to the carcass changing shape) may not happen for many miles. If the tire is changing shape, you would be able to see that by having the wheel/tire on the rear, where you can spin it - and comparing it with a good tire.
If you take it to a tire place or repair shop, they could find the tire imbalance by rebalancing the tires. One of them will need far more weight than it did previously.
Although I think it is most likely a bad tire or bent wheel - it is possible the problem of a slightly unbalanced tire or bent wheel could become much more noticeable for other reasons:
It can happen if a wheel bearing is bad - but to be that bad, it would have been making a growling noise for a long time.
Not as likely, but it could also be that you have a loose suspension bushing or a loose ball joint - which would be a very bad ball joint - and the looseness was allowing the shimmy to be noticeable, when it wasnt previously.
A CV joint that is bad can also cause vibration - but to be that bad it would have been making clicking noises on each and every turn for a long time.
Good Luck...