Let's figure out this Vibration

[shaferbm]

I've been trying to refrain from making a separate thread for this, but alas here it is.

I've got a bad vibration/clunking that seems to be coming from the rear end. It get worse when I let off the gas and/or when I'm braking lightly. It also gets worse with higher road speeds. Under power its still there, but definitely less noticeable. The front end has new control arms, tie rods, CABs and sway links, so we should be able to isolate this to the rear.

I intend to replace rear trailing arm bushings and subframe bushings when I install lowering springs, shocks, and their associated bearings and mounts so this is just to reaffirm that the problem will be fixed.

I've been underneath and haven't discerned what the problem is yet. How do I nail this down to CSB, guibo, subframe bushings, etc?

The car is not being driven right now, because I don't trust it/don't want to cause more damage.

[jalopi]

The safe way:

If you know someone with a lift, put the car up in the air in first/second gear - whatever it takes to get the rear wheels up to 20mph. Use a stethoscope on the diff and both hubs. If you don't have a stethoscope, harbor freight sells em pretty cheap.

The not-so-safe way:

Same thing as above, but minus the lift. Just make sure you've got some really beefy jackstands set on solid ground... in any case, doing this will at least eliminate the diff or wheel bearings if they're not the problem.


On another note:

I know it might sound a bit crazy, but I've seen rotors before that were so out of round that they made a clunking sound going down the road, getting worse as speed increases... only seen this once, but who knows? Just throwing some ideas out there.



*EDIT*

I doubt it's the bushings, but if you don't hear any grinding/clunking noises coming from the diff or the hubs, grab a mirror and a good light. Go under the car (not jacked up) as best as you can, from under the rear of the car so you don't get run over, and have a friend put the car in 1st, fully depressing the clutch & brake pedal. Have them keep the brake pedal fully depressed and cycle the clutch from fully depressed to the point of almost stalling out - otherwise known as power braking. You'll be able to see the driveline flex pretty good if the bushings are shot.

[Earendil]

Sounds like what my drive shaft did when the U-Joint gave up on life. There was a position where the U-Join was "balanced" and a position where the U-Join was very "unbalanced". Acceleration or Deceleration would cause the U-Joint to shift, and end up in one of those two positions. I was never able to physically move it, but a very close visual inspection with good lighting showed that the metal was very worn and starting to tear. I replaced it asap.