Need some help in diagnosing a shimmy.

[TrueBlue]

1994 AWD 5-sp, NA.

Car starts shimmying around 50 mph or so, not noticeable below those speeds. It shakes no matter what gear (3rd, 4th, 5th) or regardless of if the clutch is in or out, or if the trans is in neutral or not. Shakes while braking until you're below the 50mph threshold, too.

Only seems to occur after it's driven for a while, 5 or so minutes. Comes and goes.

No odd noises are heard (i.e. squeaking or whirring)

I thought it was a balance issue, so I took it to a shop to get the 14" OEM steel wheels with tires, rebalanced, rotated, and retorqued. Occurred again less than 24 hours later.

I think it's rotational. You can feel it all through the car, in the steering wheel and in the shifter.

Thoughts, comments? I've had to park her

[log1call]

Sounds like wheels. Could it be an axle? To diagnose it you need to figure out what speed it's at... wheel/axle revs, motor revs, speed through the air related(flapping plastic cover underneath). Does it get worse or set off if you hit a bump? Does it come and go with throttle application?

If your initial impression was that it was wheel speed I would have a good look at the axles and cv joints, especially the inners.

[TrueBlue]

Sounds like wheels. Could it be an axle? To diagnose it you need to figure out what speed it's at... wheel/axle revs, motor revs, speed through the air related(flapping plastic cover underneath). Does it get worse or set off if you hit a bump? Does it come and go with throttle application?

If your initial impression was that it was wheel speed I would have a good look at the axles and cv joints, especially the inners.

Looks like it's independent of engine speed - maintaining 50 mph, I downshifted through 5th, 4th, and 3rd gears, it kept shimmying. If I pushed in the clutch, it kept shimmying too. Didn't seem to come or go with bumps.

:edit: How could I diagnose if it was CVs or axles? I don't hear any clicking sounds.

[tahiti350]

bent wheel or bad rotor... possibly u-joints or center carrier bearing in the drive shaft or bent shaft. Have you hit anything in the road lately? Slipped on ice and tagged a curb?

Jack it up nad have a CLOSE look at everything, rotate the tires and look for runout, for the front do this with the steering straight, and then turned each way until it hits the steering locks.

[TrueBlue]

I had thought bad rotor... I've replaced brakes on both a Chevy Cavalier and a Toyota Highlander and that cured a shimmy before. Hmmm.

I think I can rule out bad rim/tire assy as they were rebalanced and remounted. I told the guy I had a shimmy issue, he said there was no out-of-balance on the wheels afterwards.

Haven't hit anything with the car. I really have to get it jacked up and take a look, I think this weekend I am going to put pads/rotors on anyway as they're getting low.

In the CV/axle area, what should I be checking for?

[evolutionmovement]

They can still balance out when they're bent.

[log1call]

The inner front cvs get a bit of play where they fit onto the gearbox, that would be a good place to look. The trouble is that they all have a bit of play and it takes experiance to decide whether they are the problem or not.

If you get a piece of sticky tape and put it on a wheel you should be able to hear it flap as the wheel goes round. If the shimmy is at the same frequency as that then it will be a wheel or axle. If it seems to be about four times faster than the tape flapping then it will be your driveshaft to the rear diff.

If it seems that it is wheel/axle speed then look at the cvs and axles. Any torn boots? Grease leaked out?

Check the shock absorbers... are they dry? No sign of leaks?

Check the disks. Turn the wheels slowly while someone slowly presses the brake pedal down. Any surgiing in the wheel turning?

Check for play in the steering. turn the steering wheel left and right an note how much play there is before it moves the left and the right wheel.

[tahiti350]

I have a similar issue with my white wagon, but have swapped tires with the wife's car and it was much better. Mine is a noticable, but minor shimmy in the steering above 40 mph, worst at around 55-65. It transmits noticably into the steering under braking. There is no feedback thru the brake pedal to indicate a warped rotor.

Try swapping your wheels/tires front to rear to see what that does.

Or, put the spare on and drive it. If it still shimmies swap the spare to another corner and try again. This will tell you if it is a single wheel/tire problem.

Brake rotor "normally" won't shudder under cruise conditions unless the rotor is way warped, as the piston will push back into the caliper to provide the needed clearance. They will shudder under braking obviously. Is there any "pulsing" thru the brake pedal when braking?

[TrueBlue]

The inner front cvs get a bit of play where they fit onto the gearbox, that would be a good place to look. The trouble is that they all have a bit of play and it takes experiance to decide whether they are the problem or not.

If you get a piece of sticky tape and put it on a wheel you should be able to hear it flap as the wheel goes round. If the shimmy is at the same frequency as that then it will be a wheel or axle. If it seems to be about four times faster than the tape flapping then it will be your driveshaft to the rear diff.

If it seems that it is wheel/axle speed then look at the cvs and axles. Any torn boots? Grease leaked out?

Check the shock absorbers... are they dry? No sign of leaks?

Check the disks. Turn the wheels slowly while someone slowly presses the brake pedal down. Any surgiing in the wheel turning?

Check for play in the steering. turn the steering wheel left and right an note how much play there is before it moves the left and the right wheel.

Great post. Some of that I knew, some of that I forgot, much of that was new, and all of it appreciated. Thanks.

Tahiti, the wheels have already been rotated, no effect. I thought one may have been coming untorqued, not the case.