or jack up you rear end, mark you tire and mark you driveshaft. see how many times the driveshaft spins to get one revolution of the tire.
Do this with a spool or welded diff.
BUT if you have an open diff or locker do this with one tire on the ground but this time you have to do 2 revolutions of the tire and then count the number of times the driveline spins as indicated below.
4 turns + less than a 1/4 turn should= 4.10
4 turns + about 1/2 turn should = 4.56
4 turns + a little more than 3/4 turn should = 4.88
5 turns + about a 1/3 turn should = 5.29
You get the picture.
