I have been hearing a clunking noise coming from my rearend of my '81 280ZXT. I originally thought it was my passenger side rear park brake dragging, but have since disconnect & replaced the worn pads. The noise persists. It starts off at about 15 mph and get faster as I speed up. Any suggestions?

 

use search you should find the answer, but its most likely its going to be your diff mount going out

 

is it a definate clunk?, my muffler is falling apart(previous owner put a cheap one on) and i got pieces of metal and rock that rattle around in it but only past 1500 rpm

 

Do you mean the mean the isolator or the mount itself? What should I look for to identify the problem?

 

Either the diff mount, half shafts, or driveline u-joints.

The diff mount is the rubber / metal bracket connecting the diff cover to the frame. Check it for cracks. Also while under the car rotate the half shafts & driveline by hand to check them.

 

Is this a common failure? I haven't had a chance to look at this yet but is definitely an annoyance. What is a worse case failure?

 

Yep... SEARCH for "clunk"