I started noticing a clunk - only under hard, WOT accel. Will happen going at 70 or from a dead stop. Will do it stopped with the brake on as well. It almost feels like someone if bumping you from behind but you feel it on the shifter.

I have an 89 GTA 5.7 with about 500 miles on the following mods: transgo shift kit (the more expensive one), ZZ4 cam, Vortech heads and TPI vortec intake, AS&M runners, ported intake, bigger TB, custom PROM.

I have an appointment to get the car dyno tested next week and I'm not sure if the numbers will be off because of this driveline issue.

I had someone power brake the car while I looked underneath and under the hood, and I didn't see any movement that was out of the ordinary. Also, no bump at all under partal throttle - you have to really be standing on it to make it happen.

thanks in advance for any insight!!

Check your trany mount and your torque arm mount .

did more searching and saw that that's a good place to start... thanks.

Your welcome . My car is a 5-speed and it was doing that really bad all the time because of shifts and once it was the torque arm mount then again when the tranny mount went .

It was the trans mount - never had one go like that.

It's pretty common for hte trans mount to go bad and do that int hese. I suggest everyone go to a poly mount.

my car to clunks when it shifts. i have a 700R4 with a stout shift kit in it. with moderate throttle it clunks adn shakes the car. at wot it feels like something is hitting your hand whenit shifts, sounds liek i need to look at the trans mount. any suggestions on a good quality poly mount?