Technical rear end clunks when auto trans downshifting to first.

I have rebuilt everything on this car it is sbc 2004r and auburn posi in a 8.5 10 bolt. When it down shifts into first there is a clunk from the rear end area.

Any thoughts?
Greg

 

tv cable needs adjusting? u-joint? drive shaft correct length?

 

What is the vehicle ????????

 

U joint?

 

Can you get the rear wheels up and verify the noise is from the rearend? If so I would be looking at the bearing retaining caps to see if they have loosened up on you. If the sound is actually coming from the trans, then there is a good chance that the shifter is not adjusted correctly, trash in the valvebody, low fluid pressure or even a busted fiber washer allowing too much clearance in the gear train.

 

First (and easiest) thing to check.

 

This, also make sure your wheels are tight

 

When you rebuilt the transmission did you remove the spring in the 2nd gear servo? That will cause a 2-1 clunk.
Does the clunk occur under power like going up a grade? Is a lift foot clunk like stopping at a light?