Rear end noise

I recently replaced the rear end of my 68 Camaro with a 12 bolt posi.
The problem is when I drive the car I can hear a clunking noise coming
from the rear end. What could be causing this???

Were you certain to put the "posi additive" in there? The clutches in the posi will make clunking sounds when the lube isn't used. You can get the good stuff from any GM dealer.

I did put the additive in just one tube maybe two would work better.

U-Joint maybe? At what speeds? Normally only one bottle of 1052358 GM LSD additive is enough for the rear end.

It makes the noise at low speed I haven't driven it
above 5 MPH. The additive I used was brandx off the
shelf. I didn't think that would make a difference.

Radarman, we've seen hit-and-miss success with the aftermarket products. The GM is a known quantity. Does it make the same noise in reverse? Or is it possibly more pronounced in reverse? If so, the posi is certainly the culprit. Check your u-joints closely, too, as previously suggested.

just pack it with sawdust! That will fix it!

Is your pinion angle correct? Did you build it yourself? Rear ends are difficult to get 'just right' if you are inexperienced with them. Check the u-joints for bad needle bearings and make sure to lubricate them. (I've been known to install u-joints and forget to grease them)

I didn't rebuild it but I will check the u-joints.
I drove the car yesterday and it did seem to quiet down
but now it makes noise wen I take a sharp turn.