changing diff gears

[SUX2BU99]

^ Righto. A good way is to do the trick of putting both wheels in the air and if you spin one tire and the other spins in the same direction, it will be a functioning posi. If you spin it and the other spins the opposite way, then it's either an open diff (non-posi) or it's a worn-out posi. The 3.40 posi I just put in seems to be worn out since when I do that tire spin trick, it goes the opposite direction 

[chrpmaster]

Just today I swapped the 4.10's in my shortbox out for a rear end with 3.07's.

So did you swap the entire rear end or just the final drive?

[bob77]

I swapped the entire rear.