At lower speeds, the car is wiggling from side to side, especially accelerating.
At highway speeds it's just an annoying shaking. But it is getting worse.
I have ruled out bent wheels and loose lug nuts. I can't see anything wrong under there, so I'm wondering if maybe it is losing a bushing from one of the trailing arms.
Any other ideas I'm missing?

 

It could be a bent axle. Have you tried jacking up the rear (stands under the axle tubes) and running it in gear to see if you get the shake? Make sure the front wheels are well chocked. Or use a dial indicator on the wheel or disk if you have disk brakes. At least visually inspect the bushes. Plus the torque arm bushing.

 

I was once told, low speed wiggle come from the front end, high speed the rear. thats is about 90% true when I had to track down similar.

 

Can't be either axle shaft because that would cause one brake to drag, at minimum. Can't be a bent axle housing, because it would kill a tire or wheel or both before the housing would bend. Can't be the torque arm bushing because the wiggle is side-to-side. I checked the panhard. Isn't happening on braking, and no front end clunk at potholes, so it isn't a front lower control arm bushing. I'm about to pull both trailing arms.

 

Not necessarily. The caliper essentially floats so could move with the disk. I only detected my bent axle with a dial indicator on the disk.

 

I doubt this is the problem, but back in the late 70's I had a set of Remington radials on a 76 Camaro that made the car wiggle at low speed like a bowl of jello. Come to find out the bands (or whatever there called) had slipped causing the problem. Replaced the tires and problem solved.

 

Might have a broken belt in a tire or two

 

Belts is what I was trying to come up with. Not sure where I got "bands".

 

id say broken belt in the tire as well, seen it way to many times and sometimes not noticeable at first glance but if u look at the tread closely while spinning the wheel u can see it float up and down

 

it wasn't a Camaro- 94 Chrysler LHS- but i once had a right rear tire with a separated belt that caused the steering wheel to shake like crazy but wasn't noticable anywhere else in the car.. i looked at everything in the front of that car looking for something that was bad, and only noticed the bad rear tire when i was laying under the rear of the car trying to figure out where the fuel filter was.. i guess what i'm saying is that maybe your problem is at the front of the car and it just shows up as something in the rear for some reason..

 

Have you tried swapping wheels around to see if there are any changes? Tried to borrow good wheels? Measured the run out on disks?

 

First thing I did was drive the car to BestTire, where fellow-third-gen-owner Trevor put all 4 of my wheel/tire assemblies on the tire balancer machine and spun each and every one up to speed, one at a time. No problems.
I'm trying to decide whether to go with entry-level non-adjustable mild-steel tubular arms with poly bushings, or just have done with it, now and forever, by getting chrome-moly, aluminum-bushed, double-adjustable, arms offset for more tire clearance.
Also can't decide between black for stealth or red for showing off.

 

Having balanced wheels/tires doesn't tell you if anything is broken or loose or too worn. Plus it won't tell you if you have a bent axle or badly worn/damaged bearing.

 

Putting wheels on the spin balancing machine WILL show if a wheel is bent. And ANY impact severe enough to bend either an axle shaft or the axle housing WILL at minimum bend a wheel first! EVERY time, without fail, NO exceptions!

 

So your wheels are good. What else have you done to diagnose the problem? You say it can't be this or that because you don't think the symptoms match but what have you visibly and physically checked or tested or measured? You can install "chrome-moly, aluminum-bushed, double-adjustable, arms" but if they're not the problem you'll just be poorer and still doing the "hokey pokey".