Help with occasional "thud" coming from rear end.

[killer8man]

Ok, so here's my setup...

'71 Charger with stroked 440, TKO600, 8 3/4 rear with 3.55:1 sure grip, 33 spline axles, Wilwood floating 2 piston discs. I've been using the car for autocross and after this last weekend, there had a been a pretty loud thud coming from the rear end somewhere. The yesterday, I was out for a cruise when I decided to get a little greedy coming out of a stop light. I started off easy, but then gradually put it to the floor. When the wheels broke loose, I shifted into 2nd gear and there was a REALLY loud thud that shook my bones. I instantly let off the gas and gradually reapplied and everything seemed alright, but I still get that other thud when I'm in a turn. The big thud could have been just a bad shift somehow, I'm no pro, but I've never heard anything like that before.

Any ideas on where I should start looking? Should I pull my axles out? Take the pumpkin off? Might it be something with my transmission?

Thanks ahead of time for all of your help!

Adam

[Just 6T9 CHGR]

Pinion snubber adjusted too far from floor board??... getting on it causes the axle to wind up & snubber slam into floor?

Bad leaf spring bushing?

[killer8man]

6T9,

Pinion snubber is about an inch from the floor board. Is that too far? Leaf spring bushings look good from what I can see. Should I pull the spring out to get a better look?

Thanks,

Adam

[Just 6T9 CHGR]

Inch sounds about right.  The rubber bumper on it is in good shape right?

Is the Sure-Grip a clutch or cone type?  If its a clutch type, the clutches could be sticking?  Last time oil was changed to include a bottle of friction modifier?