Thumping rear brake noise

[kkvette]

Hi!
New to the forum
I have a 92 LT1 convertible.
It has had this annoying thumping noise when applying medium brake pressure since I bought it (with 27K mi). It's coming out of the drivers side rear.
I have checked rotor for run-out and it seems fine. I have replaced the spindle and bearing carrier. The only thing left is the caliper, I guess?
Anyone else had this problem? It thumps and also pulses . If you hit the brakes hard it goes away, and light brake application also had no sound.

I looked at the caliper with the pads off and it looks like the piston wiggles in the bore? Not leaking any fluid. Trying to take the caliper off, but educating myself on Parking brake wierdness. Haynes manual pathetic on auto-parking brake dis-able to get caliper off. Printed off a post from this site, will try tomorrow.

I was thinking about just getting a new caliper. Pads looked OK, but running out of options. Also the car was in an accident, but I don't know anything about it.

Thx!

 

[Eagle85C4]

It may not be brake related. Check everything under there for something loose...bad bushing loose shock......and u-joints on the half shaft...

 

[kkvette]

Eagle

Thx for the reply. I will ckeck other thinks out, funny how it is OK under power, just makes the noise with medium braking applied?

 

[Eagle85C4]

Forgive my manners...Welcome to CAC!!!!

 

[WhalePirot]

a light or heavy thumping sound?

A heavier sound might indicate unloading ot a U-joint, just enough to allow it to wobble. Heavier loads, either braking or accelerating could allow it to 'seat' and make no noise.

Seems low mileage for a U, but stranger things......................

 

[kkvette]

Glad to be here, Thx!

Is there a way to tellif the U-joints are bad? If I put a crow bar between the studs and try to move the axle froward and rearward will I see movement in the u-joints?
How about loos shock test?
Anything else I should do/look at?
Thx
larry

 

[Eagle85C4]

If you jack up the rear of the car...just moving the wheel and or rotating it back and forth will tell you a lot...

 

[kkvette]

Still Confused

I have the wheel off, car jacked up and caliper swung away.
I put a bar (with towel) across a couple studs and moved the axle forward and backward. There was a little play, but it looked like it was in the 3rd member. Eveything else looked tight. No movement in shock, u-joints etc.

Also I can make the thump-thump-thump happen while going down a hill while having the stick in neutral and applying medium pressure to the brakes. Doesn't that pretty much eliminate everything but the brakes? If I apply the brakes with no opposing force from the engine through the 3rd member, wouldn't that eliminate the u-joints since there would be no pressure on them?

More ideas?
Thx
larry

 

[kkvette]

Break out the check book

Happy happy joy joy.
Well replace two rear hub/bearing, one LR outer tie rod, one LF hub bearing and turn four brake rotors with excessive run-out!
Once fixed and a four wheel alignment, I should have no more thumping, a much nicer driving car, and less money to worry about!

 

[Rabbit]

Did you check your shock mounts?

 

[kkvette]

Rabbit, Thx

I actually gave up and took it into a guy here in Seattle that is a guru, but thx for the effort and thought to suggest something.
I will post how it drives once I get it back!
Thx
larry