I just removed my 8", seamed like I only filled up about 3 or 4 inches of a 1 gallon milk jug of the oil that I drained out of it. Previous owner may have either not have put enough in, or the shop that sold me the new posi over stated the amount of fluids I would need. He sold me 3 quarts, and told me that's how much I would need of the 80W-90. He also sold me a small bottle of the friction modifier too. Is 3 quarts way too much or the correct amount?

 

I think the capacity is a little more than 2 qts, so you'll need three the bottles.

Only getting a pint out of the diff is little bit worrisome. Where did the rest of it go? Jack up only one side of the diff, so oil can drain from the tube into the pumpkin. Do the same on the other side. I bet there's some in the tube, but not that much.

If you have a limited slip diff, you'll need the additive. If you have an open diff, you don't need it.