1974 rear end noise

[cams74]

I have a 74 with 3.36 rear and it works fine until it warms up and then when I start out from a stop the rear end really chatters almost grinds it does not matter if I am turning, straight or in reverse. I have changed the oil and did add the posi trac lube, did not help. No highway noise, only does this up to about 10 mph. Any ideas?

 

[73shark]

Need to do some figure 8s in a parking lot to work the posi-additive into the clutch pack.