I have a 10 bolt rearend and what are the factors that make a posi or is it just a limited slip. The #'s are 1129
                                9799700
I had the back off,but don't know what to look for. Plus what happens if you turn one of the axles?

Hmmm, little bit tough to explain but if you have the cover off, look for springs between the gears. You look through the opening in the center section of the differential.

If that does not explain it well enough I can see if I can find a picture of what to look for.

It should look similar to this.

-- Edited by Carl Stevenson at 13:57, 2009-03-06

Thanks Carl. No springs, so it's not a posi.

You turned it a half turn and looked in both sides?

No I just felt the other side for springs

Ok, just wanted to make sure because I wasn't sure I had been clear in my explanation.

for what it's worth, I had the diff casting number written down from a friends 70 GTO 400 4 speed rag.  I wrote down 9799100, but the 1 might be a 7 as in your 9799700.  The casting number will not tell you if it's posi, you've done the right thing by looking for the springs.