rep69Hello. After driving my 1969 for approx 20/30 mins I hear a thumping sound coming from the rear of the car, when I accelerate from a stop and turn the wheel. Any suggestions? Anyone know a good mechanic in the Norfolk, VA area that knows how to work on C3 corvettes? Thanks Bob in Suffolk,VA
BillHannaFantomworks are in Norfolk and love working on Corvettes -- their shop always has a lot of Vettes in it.
They used to have a TV show that was very interesting. Dan Short and staff do meticulous work that they are proud of.
Their web site is: fantomworks.com
manchestershark
Could possibly be trailing arm bushings. How is tire ware? Also the nose cushion on the differential brace could be worn and loose.
F4Gary
The nose cushion was my first thought too.
KentvetteukWhen you say a "thump", is that a dull thud, or a harsher, almost metallic banging?
If it occurs when you are turning my thoughts would a U/J failing, or the diff needing a fluid change.
The latter becomes evident when the diff warms up a little and the car has been running in a straight-ish line for a few miles. It'll normally "crack" a few times (the posi clutches "stick") then settle down until you do another long straight run. Drain and refill with good mineral gear oil and two bottles of the GM Diff additive.
Phil's-StingrayMy '75 roadster 3:08 diff positrac did that while making a left turn. My shop replaced the fluid with new positrac gear lubricant. It resolved the issue!
My friends '68 roadster 3:08 does the same!
Changing the diff fluid with a positrac lubricant may resolve your issue.
Hope this is helpful!
manchestersharkI changed the fluid in mine. But only after a bunch of other preventative repairs. There was no drain hole in mine. So.. I drilled and taped the bottom. Total drain, flush with carb cleaner and kero. Put a flush plug in it. Filled with 80 oil and two pints of GM positrac fluid. Did about 10 minutes of figure 8s in a parking lot, good to go. No problems!
F4GaryI think bad u-joints will make a chirping/squeaking noise when turning in a circle. Don't think they clunk.
I towed a boat with my '78 and eventually they started chirping and got replaced.
manchestersharkIf U joints made a clunk, they would be on the ground under the car. A quick peek would tell you if they were bad. Check all four for looseness or missing parts. They are not really hidden.
Norsky... Did about 10 minutes of figure 8s in a parking lot ...
Every spring after the cars sat all winter this was an exercise that all would get before any serious driving took place - forward and reverse. Was fortunate that no one ever called the local law enforcement kids for my doing "crazy stuff" in a parking lot...!!!
Jim Olson 
"The Toys"...!!! Save the Wave! 
rep69Hey, Yes its a dull thumping sound, almost like something is too tight and binding .
KentvetteukI think a fluid change is the first port of call - inexpensive and relatively easy, with a small pump (no drain plug).
manchestersharkDepending on how long fluid has been there, change it regardless. I would have to hear it, or feel it. But, I think it's a worn or loose piece that transfers vibration to the body/frame through a rubber mount or suspension part.
BillHannaMy '75 was making a snapping noise in the rear end when turning. I changed the diff fluid and added positrac fluid. I forgot about this until this post and I realized it was not longer making that noise.
KentvetteukThe first time I encountered this was after a 150 mile drive to Donnington Motor Circuit, in the UK, on a motorway (freeway). As we turned into the circuit it sounded as though someone had taken a hammer to the rear end somewhere! It was finer while we were going around corners, but after a while on a straight road it would bang again when we turned, although not as loudly as the first time! I did the the fluid change and the problem was cured.
Given how expensive, and difficult to repair, some rear end issues are, a fluid change is a quick and cheap fix!👍
manchestersharkWonderful! The easy route is the first route. Glad it worked out and problem had been rectified.
