Clunk noise in rear

is it a swing axle or IRS?  Check the shock mounting bolts. I had a car that someone put a U.S. thread bolt and even though it tight it had enough movement to make a knocking or clunk sort of sound. Is this a new sound or have you had it since day one?

wrong shocks? check spring plate and torsion bar retainer,check spring plate bolts to axle and also check IRS bolt which attaches the arm to the pan

Anthony mentions all great stuff.  

 

Also have someone check the tightness of the two rear wheel hub nuts.  They should be torqued up to 280 ft. lbs. or so.

How are the bumper brackets looking? Is there a chance the rear bumper or something similar is flopping around / up and down as you go over large bumps?

OK guys, all good suggestions.  It is swing axle, and I have checked all of the above except the bumper brackets.  They seem tight. It really feels suspension related.  I did install rear bump stops when I got the car as they were missing, so I know its not bottoming out. It really sounds like when you hit a bump and the chassis goes back to normal is when it happens. Could it be rear torsion bars loose?  How do you ck those? Thanks.

There is a horizontal mount plate on the L & R rear of the speedster body frame work that is bolted to the top of the rear suspension tower forward of the shock. These come loose and the body "clunks" now and than...tighten the bolt on each side and take it for a ride...I'll bet pocket change ~

Great! I'll check those. Thanks

When this noise occurs is your foot on the accelerator pedal or did you ease off it. If your foot is backing off the pedal it could be backlash or the axles slapping against the fulcrum plates. This would one of the last areas to check. how much is the car lowered? Are the shocks bottoming or too short and topping out?

Throttle makes no difference. I am pretty sure it is not topping out although that could be a possibility.

Frank:

 

You could take the "Car Talk" guys' approach and have one of your volunteer neighbors hang out over the back of the car as you drive around so they can see what's going on, right?  OK, maybe not.........

 

In lieu of that, maybe you could get that same neighbor to bounce the car up and down as much as possible while you look and listen underneath to see if/where it's clunking.  Maybe two neighbors, one on each wheel well?

 

Those rear suspension clunks are a pain to find.  It could be as simple as a shock absorber that's lost it's prime from sitting for a long time and then getting fully extended when you had the car up doing the valve job.  That sometimes makes them clunk.  

 

Try this.....Remove the shocks entirely, then take a short (not spirited) drive over some bumps that you know caused the clunk before.  If it's gone with no shocks then consider replacing them.  If they're relatively new (like less than a couple of years), then take them one at a time, held upside down, and fully extend and then fully compress them five times and replace them on the car.  That might fix it (if it's the shocks).

 

The only other thing that hasn't been mentioned is a failed front transaxle mount (torn rubber) but that's down a bit on my suspect list.

 

This just reminds me that I have to get off my butt and get my seats finished so I can drop by and visit!

Rear disc brakes?

Drums. I have to drive it some more. It just may be topping out. I tried bouncing the rear end and it is quiet. I looked to see what it would be clunking on if it topped and the spring plates can bang in to a stop cast into the torsion bar/shock mount. This would make the sharp metallic sound it makes and it has touched those stops but this may have happened on the numerous time I jacked up to make the Stiffy kafer bar fit with my heat exchanger. So that is inconclusive. Oh, also the axle nuts were torqued to spec and I can't feel any play in the axles.  Gordon, the shocks are making that hydraulic sound when I bounced it so I think they are fine. They also are damping properly. I'm sure the nose cone mount is OK as it is new and I have one of those braces under the trans to stop that from breaking.

Did you tighten down the 2 body bolts at the horzontal rear mounting plates?