I've read all the comments about worn out parts causing the rear clunk but mine is just the opposite. I have a 1978 280Z that made no rear clunking noise what so ever with the old rubber bushings. I just replaced the mustache bar, inner control arm and sway bar bushings with energy suspension poly and now when getting on and off the clutch I get the clunking. I used lots of grease and I torqued all the bushings down to spec. When I dropped my diff down, I did notice a piece of thick rubber fell off the top of the diff ander the arrestor strap. I put it back in where I thought it should go. Is this a factory piece (it looks kind of like a piece of tire rubber) or did a previous owner put it there to eliminate the clunk in the first place? I now have a better handling car but also have the dreaded clunk!
Thanks,
Dan

 

Yeah, the po was using that as a bump stop. Your front diff mount is broken.

 

Scroll down the the bottom. This should take care of that pesky bump ~

http://www.arizonazcar.com/diffmount.html

JM

 

These are really nice! I'll put them on my wish list!