This has been going on as long as I've had the car (wow almost 2 months?) Its an 87 GTA, 700R4 with the 9 bolt rear end Car has an energy suspension poly trans mount When shifting to drive, or if I'm cruising along not under any load and push the pedal down, theres a "Clunk" from under the car (havn't pinpointed it) before the car accelerates. I'm ruling out the tranny mount because its an energy suspension poly one, and when I was under the car putting the rear sway bar back in, I checked the u joints and they seem to be good. One thing I did notice was that with the rear of the car off the ground, if I turned the driver side wheel, it didn't immediatly turn the pass side wheel. I'm no expert on rear differentials, but I would think that a good rear end would be pretty tight (ok we're talking cars here so stop thinking that way), and there wouldn't be any play between the two. Any ideas on how to figure this out, what it might be? Thanks

Might be your shocks. At the drag strip, when my car hooks, the rear bottoms out.

If its just a little clunk, and happens even on little acceleration, it might be a ball joint. However, if its a ball joint, it should also clunk on braking and turning. Not always, but usually.

what the torque arm mount look like

+1

if it occurs when shifting from park to reverse or reverse to drive or drive to reverse and sounds like somebody wacked your floorboard with a hammer. You my friend have a torn torque arm mount bushing.

Dont bother buying a stock replacement, get a poly one (they usually are less than $20), and fix it for good.

Look under your car, follow the torque arm along the drive shaft to the front of the bar, there is a mount attached to the trans, this mount has a rubber bushing, most likely it is trashed. Not the direction the edge "lips" of the torque arm face (either towards or way from driveshaft) you'll need to know that when you get a new bushing.

Interesting, I hadn't thought to check that.
What about the thing with it taking some time for the other wheel to start spinning when I turn one side? Also, the posi seems to work based on my "driveway testing", but when I was turning the wheel clockwise, the opposite side was going counterclockwise....

thats normal..posi traction wont engage until enough torque is provided hence "limited slip" if it was full locking differential both would spin same direction

I'm having the same exact problem with my car clunking...... i thought it had something to do w/ the driveshaft shifting, but i'm gonna take a look at the torque arm bushing now.......

while youre under the car, doesn't hurt to check the U joints too.

checked everything...... and it all looks fine....... i popped it out of gear, and spun the driveshaft back and forth with my hands, and i felt a decent amount of play...... i dunno

I had/still have the same exact issue. I don't think it's the torque arm mount. I replaced mine with spohn's tranny xmember mounted one and actually, I have more "clunk". There's 2 distinct ones now though. One from the TA moving in it's mount and the second from.... dunno! I too saw a 'decent amount of play' while under the car when manually turning the DS. One would think, that after all these years of these F Bodies being around, SOMEONE would be able to give the answer! My mechanic thinks it may be excessive lash on the pinion, but I haven't gone that route yet. Soon though.

well my car does it a little bit, only when I really hit the gas it may do it, I replaced the TA bushing with an energy suspension one and while doing that started the car whiles it was in the air, there was excessive movement in the differential even with the brakes on. The driveshaft turned about 2 full rotations without the tires moving, and the u joints looked tight, and the new ta bushing is tight. So I think it is maybe the ring and pinion being worn and slipping a little or just the splines are worn.

well i replaced my pan hard rod and my torque arm, with BMR stuff, and my clunks went away for the most part

Ok then other sources of odd "clunk" sounds from the undercarriage....

Worn tailshaft bushing...although if its worn enough to make noise/vibration, you usually have a tranny fluid leak there too

Worn bushings on the rear control arms, or possibly loose bolts allowing the arm to travel about when the suspension works

Exhaust too close to axle or broken exhaust hangers letting the pipe bang into stuff.

Broken sway bar end links, typically you hear a nice healthy bang when cornering or when the suspension travels.

Check exhaust heat shield by fuel tank, it can rattle and bang if loose

Those are all places I've found making noise on 3rd gens, also keep in mind that these are mass produced unibodies that are at the newest pushing drinking age, so they are prone to odd squeaks, groans, and rattles. Especially when you have tweaked motor with a lot of torque that makes the whole car flex