Strange, rhythmic shake coming from rear of '01 ZX3

[Contraband]

Hey folks, I've been dealing with this problem for a while now and cannot for the life of me figure out what's been causing it. I've got a 2001 Focus ZX3 that exhibits a strange, timed wobbling or swaying motion around right turns. I would hesitate to call it a "shake" or "shimmy" because it doesn't feel like it's happening very fast - definitely not as fast as the wheels spin.

I've noticed it mostly on the freeway, where at around 55mph and up, going around a slight right turn will get the car to start it's motion in the back. For the most part, going straight doesn't affect it, and it seems if there are grooves in the pavement it they will upset the car. One factor that seemed to affect it quite dramatically is how much weight the car is carrying. If it's just myself with no cargo, the problem is mostly easy to deal with. However, if I have a passenger or two, or as I found out a few weeks ago, all my belongings on my way down to school, it will cause it much more dramatically. In the case of the latter I noticed it driving the ~300mi down I-5, which is almost entirely straight - yet the car was wobbling almost the whole time.

I don't feel any vibration in the steering wheel, and because it happens around right turns, I'm inclined to believe that there's a problem with the left rear suspension. As for mods, the car has a Koni (Yellow) Sport Kit and a stock-SVT rear swaybar on it, but I remember it exhibiting the same behavior back when I had the stock suspension still on it. I've rotated the tires in the same time it's been doing this and it still does it which leads me to believe that the tires aren't to blame either.

Between the fact that it feels like the rear wants to steer, and that it will tramline on grooves in freeway pavement, I think it's a rear toe problem. I'm not entirely familiar with the control-blade rear suspension the Focus has (the semi-trailing arms on my BMW are way less complicated ) but reading this thread tells me that, in a best-case scenario, this setup WILL change toe as the suspension loads.

This makes me think that maybe, just maybe, the bushing for the longitudinal control blade has failed or something? In any case I'll be tearing apart the rear suspension this weekend, but I just thought that I'd post a thread to see if anybody's had experience with this or if anybody has some helpful pointers.

[hEaT]

Sounds like an alignment issue and possible rear suspension bushing failure.

[Contraband]

I was kind of thinking it was a bushing failure. Are the bushings in the rear suspension integral to the control arms/blades, or can they be pressed out and replaced?

[hEaT]

They can be pressed out and replaced. Not a job for a bench vise though.

[Contraband]

Despite the fact that Autozone's spring compressors won't fit on the rear springs () I've got the part of the rear suspension apart that I wanted to check. The forward point of the longitudinal control blade looks like the bushing is in fine shape, so I don't know where to look next.

Suggestions?

[Contraband]

I just found this thread and guess what - I have a front swaybar endlink that has a totally destroyed socket. I'll pick up an endlink from the junkyard tomorrow and report back with findings!

[Contraband]

I replaced the endlink this afternoon with the later, aluminum style and the problem is still there. Could it be a steering rack bushing?

[slomustang50]

I am interested to find out what your problem is as well. I have a similar issue at high speed where the car seems to walk back and forth. Strange thing is I don't feel anything through the steering wheel either.

I am going to try the endlinks and possibly the strut mount and bearing. May do the struts as well.