I have a 76 vette and it has a werd problem not allways mostly when hot or warm it has a clucking at low speeds its on pas side rear if i back up and stop it clunks and if wheels are strait it dont do it as bad but back up and turn wheel and clunk clunk clunk clunk sounds like something hiting the caliper so i re built the rear end all new parts like yokes bearings seals new pin in possi unit and gess what it still does it and new calipers and brakes i thout it mite be possi sticking so i re built it and i also add 2 bottles of trac aditive dont do it going down hiway just at slow speeds feels like it mite fall off so dam werd stumped please need help

 

Could be something in the parking brake area.

 

you know I thinking the same thing ya see drivers side is all brand new the other is arig stuff and the parking brake ant qwite right it is too lose to hold and it is adjusted all the way on the cable and its the pas side doing this clunking sound it sounds like the half shaft is hiting somware but no marks showing prof of it hitting also caliper is new so I think ya right il tere into it wen I get done with the paint job thanks so mutch for your thout it helped

 

IMHO, check your swing arm bushings.
Hope I'm wrong.

 

After adding the Posi-Trac additive, did you do a series of figure 8s to work it in to the clutch plates?

 

The bushing at the differential support, when bad, makes a "Clunk" sound.
Check it too.