Originally Posted by Mort

To find out what gears you have you can count the number of turns of the input shaft, where the driveshaft would hook up, to make the axle shaft turn one full turn. Mark the input shaft and axle stub with a crayon. You may have to lock one axle shaft with some vise grips or something or you may not, not sure? Then turn the input shaft and count the number of full and part turns it takes to rotate the axle stub one full turn. The number of times the input shaft turns will be the axle ratio of the differential. If it has 4.10:1 gears the input shaft will turn 4.1 rotations to one full turn of the axle stub.