I redid the underside of my corvette recently and had to wait on a couple of out-of-stock parts. I had a clunking noise too, when I would start from a stop, or get on the gas in a new gear, I'd feel and sometimes hear the clunk. I'm 99.99% sure it's coming from the differential mount. It's a donut looking thing, and it was eaten up pretty badly. I'm still waiting on a replacement. Check out the status of that too. If you jack up your car on stands, you'll see the differential is mounted with a piece that looks like the hitch on a trailer. There are two circular mounts that sit in the lip part of the mount. Take a look at those. I've heard that's a common clunker!

Good luck

Imran - 74 Convt

If the noise is most prevelant when starting out from a dead stop or during a gear change, it sounds like it is a "U" joint getting the slack taken up before it engages. Easy enough to check. Get the cars rear wheel up in the air, put a jack stand under the frame and grab the half shaft and give it a twist. First one way then the other. If it will move back and forth without anything else turning along with it (immediately) , it is probably bad. Try both sides and also try the same thing with the drive shaft.

Thanks for the tips Chris. Sounds pretty easy so I'll look into doing that sometime this week.

|QUOTE|VTHokie77Vette said: Thanks for the tips Chris. Sounds pretty easy so I'll look into doing that sometime this week.|/QUOTE|
No problem Dale. Just be aware, the stuff stinks
If you get the pump, you can also use that to put the new fluid in also.

|QUOTE|Imran said: I redid the underside of my corvette recently and had to wait on a couple of out-of-stock parts. I had a clunking noise too, when I would start from a stop, or get on the gas in a new gear, I'd feel and sometimes hear the clunk. I'm 99.99% sure it's coming from the differential mount. It's a donut looking thing, and it was eaten up pretty badly. I'm still waiting on a replacement. Check out the status of that too. If you jack up your car on stands, you'll see the differential is mounted with a piece that looks like the hitch on a trailer. There are two circular mounts that sit in the lip part of the mount. Take a look at those. I've heard that's a common clunker!

Good luck

Imran - 74 Convt |/QUOTE|


Well, this worked for me. I replaced the upper and lower front differential mounts, and no more clunking. The car actually feels a lot firmer now too that those two have been changed out. Especially when starting or changing gears... Now onto the electrical gremlins :)

Imran - 74 Convt

As suggested, I would start with a fresh drain and refill with your favorite differential lube and at least one, preferably two, bottles of GM brand positraction additive. Others have written that once this is done, go to a large store parking lot after hours and drive in very tight turns to the left and then to the right. I am not talking about at autocross speeds. You are only trying to get the positraction additive to the posi clutches. Then do the same thing while backing up.

Once you have eliminated the positraction as the culprit, the other possible areas can be a bad u-joint, bad trailing arm bearing, failed shock, or even a worn half shaft yoke. Everything but the trailing arm is a DIY kind of job.
Gary