Thumping coming from rear
Thread Starter
Intermediate
Joined: Aug 2002
Posts: 28
Likes: 0
From: Cary nc
Thumping coming from rear
Has anyone else experienced a thumping sound from the rear of the vechilce. I have a 76 and can't seem to find any pattern. Sometimes when I've stopped the car and just release the brake to let the car roll forward I hear and feel a thumping. I thought it might be coming from the differential and changed the oil and used an additive to quiet noisey rear-ends but that didn't help. It could be from the brakes but I think it would happen all theime not sporatically.
Le Mans Master
Joined: Aug 2000
Posts: 9,662
Likes: 7
From: Semper ubi, sub ubi
Cruise-In VI Veteran
Cruise-In VII Veteran
Re: Thumping coming from rear (dacarlto)
You need to add GM Positrac Additive, it is in small bottles about 4 oz each. I added two when I changed my rearend fluid. Plain gear lube (even with the additive you added) will clunk and thunk without GM positrac additive. Get it from any Chevy or GM dealer. After you add it, go to a parking lot and do several figure 8's in each direction. This will get the additive mixed in with your lube and up on the positrac clutches.
Racer
Joined: Jul 2000
Posts: 351
Likes: 0
From: Stoney Creek, Ontario, Canada
Re: Thumping coming from rear (dacarlto)
If its a thumping it will be a lazy piston in one of the brake calipers. I had the same problem and it drove me crazy because I thought it was a U-joint going, but usually they start sqealing first. To be sure, pull all your brake pads and then re-install, which will require you compressing the brake pistons to put the pads back in. Once the pistons have been pushed back you should find the thump goes away. If the noise remains I would advise either rebuilding or replacing the rear calipers. Personally I would do all of them at the same time. Don't get too excited about everyone telling you to use the rear-end additives. It seems to be the fix-all around here for everyone's problem. Gm posi additive is good stuff and won't hurt anything. You can try if first but if the noise doesn't go away try what I have suggested. Good Luck.
[Modified by 76Pitter, 2:36 AM 9/29/2002]
[Modified by 76Pitter, 2:37 AM 9/29/2002]
[Modified by 76Pitter, 2:36 AM 9/29/2002]
[Modified by 76Pitter, 2:37 AM 9/29/2002]
