not fixed yet

[mlm0]

Still having a problem with my rear end, I guess I should say my 89's rear end. I have a great 89, coupe with 47000 miles with auto transmission. I have replaced and fixed everything I could find wrong with the car, except this one last problem. I will do my best to describe the problem

1. when I slap the gas pedal and let off, I get a loud clunk coming from the rear of car
2. it also does it to some degree when up shifting and down shifting not under much power
3. I have jacked the car up on all fours, and the noise is coming from near the read diff. just to where the drive shaft connects to the diff. or just to the drivers side of the diff. could not tell for sure.
4. no noise heard when under quick take off, or turning.

I took it to well known corvette shop in my area who has done work on engine for me, but not much help. They heard noise, check u joints, but thought they were ok, but not sure. Got the feeling they really did not want to mess with it. They kept telling me c4's were not worth what most owners thought they were. I can understand that, but I just wanted my car fixed and was willing to pay for it. To their credit they did not charge me for the half hour they looked at it.

I don't want to take it to chev dealer or other shop what does not know much about c4's, because I think they will just throw parts at it and cost me lots of money I do not have to spend.
If I could just figure out what it is, I could fix it or pay someone else to fix it. I love my car, but the noise is driving me nuts.

I have replaced upper and lower control rods on both sides but did not help.

sure do need some help.

 

[hcbph]

Clunk

I've had something like that once in my old Chevelle, turned out to be the u-joints on the driveshaft. Had something similar to that on my Vette, turned out to be the u-joints on the half-shafts. If you're mechanically inclined, parts will run around $150 for all 6.
If you shift out of neutral to reverse or first and you get a clunk - most likely u-joints IMO. Same thing if you hit the accelerator and let off, clunks each time there's a change in torque applied to the driveshaft. Based on what I've seen myself, seems the half-shafts are more prone to u-joint failure than the driveshaft.
It is possible it could be in the differential (incorrect pinion depth) but that usually doesn't happen except if it's been a recent repair or has a lot of miles on it.
One way to test u-joints is to grab on either side of the joint and twist opposite directions, if you can see or feel any play then it's definitely bad. Sometimes they seem good yet aren't.
My thoughts, good luck