Wicked Shimmy


#1

I’ve got a vibration issue. I’ve been after it for a while now. Still am not sure what’s causing it.



The vibration is cyclic. It occurs at highway speed. It seems to cycle from being intense enough to really bother me, to being virtually non existent. It goes through three or four of these cycles every minute, almost as if some kind of harmonics are at work here.



The tires are Goodyear Viva Touring, and they are about 20,000 miles old. 6/32 left up front, 8/32 left in back. All four were installed at the same time about one year ago. They were just balanced today. The tech. assured me that they are as balanced as balanced can be.



I’ve tested the suspension and steering. Steering freeplay is minimum, and I’ve found no freeplay in the tie rod ends or ball joints. There are some worn out bushings but that’s all I’ve found. There’s no noticible freeplay in the bearing assemblies.



All I can think of is maybe it’s the tires themselves, or the rims are no longer any good after over 17 years of service.



Any theories?



-Matt


#2

Harmonics come to mind. If the toe in/out is set very close to zero, or neutral, the small amount of movement through flex, or “play”, could permit harmonics to set in. You could add a little bit of toe-in to the wheels. During driving, when the vibration begins, apply a little left, or right, pressure to the steering wheel. If the vibration is interrupted, check for steering linkage play, from the steering wheel to the wheels and wheel bearings. A little play could go a long way. Also, worn shocks?


#3

I believe so.
But it is my understanding that worn shocks just make the car floaty.
I’m still working on my steering and suspension knowledge it’s one of my weaker points in automotive. I’m actually in a college class for it right now, but I can’t wait a semester to figure out what’s wrong. =-/

-Matt


#4

Oh! The alignment is set slightly off to the left. Forgot to mention that. Could that do it?

-Matt


#5

Try rotating the tires. If that has no effect, i6t’s probably something else.

If rotating the tires has an effect, then it’s likely the tires are out of round - and that is usually caused by a misalignment.