I have this clunk coming from the back of my car. My transmission shifts pretty damn hard, and I don't know if the clunk is from driveline shock, or if something is bouncing. It sounds almost like my gas tank is banging against the car or something, but I don't think that's possible.

I occasionally get a small clunk on the 2-3 at light throttle, but barely noticeable. The 1-2 clunk is very loud and apparent...if you guys want, I can get a video.

The rear U-joint on the LS1 driveshaft I installed also seemed to not be as loose as it should. Would a U-joint make a loud bouncing/clunking noise?

Had a poly trans mount in. Now I have a fairly new LS1 mount in, and it seems to be intact. I looked at it the other day, and I can't wiggle the tailshaft at all.

Torque arm mount is polyurethane...

 

well u dont want a loose u joint, that means its bad. tight good loose bad. that would be my guess as to what the problem is. try driving around a parking lot and getting on it real quick and let right off. if u hear that its a u joint. do a search and see what else u can find out

 

The U-joint was tight, that's what I'm saying. Not excessively tight though.

 

I get that same "clunk" from the rear, but for me its when I deccelerate from 2nd-1st. I wish I knew what it is :\.

 

same here light throttle shift of 1-2 makes a banging noise. Did it with the 4l60 does it with the th400. I was told is the shock of the stall converter when it shifts it kinda jolts the drive shaft. I say BS but it has done it with 3 trans so......I guess it has to be.

 

yeah, oh well. I'll just learn to enjoy it or something

 

Mine does the same thing, and I have poly motor and trans mounts, as well as a Jegster Tunnel Mount torque arm. Didn't start doing it 'til the torque arm. My car just shifts real hard, due to my custom shift kit. Seems to be worse when cold. I'll just live with it 'cause I'm hardcore like that.

Check to see if anything is loose maybe?

 

could it be your torque arm? some aftermarket torque arms will hit the bottom of the car back by the rearend.

 

Check the safety loop if you have one. Also check the rear trans mount. I broke 2, than went aftermarket poly, lol. It kept thumping every time I was on it. I didn't hear it at all riding normally.

 

I got the same problem as Formula_x ,the 2-1 shift,also have
the same year and model car.