Originally Posted by CapnDean
jack up the rear end: Rotate the tire one full turn and count the rotatiions of your drive shaft. That is your ratio.
If you do not have positraction (both wheels spin same direction when you spin one side) you will have to rotate your wheel 2 revolutions to get 1 full turn. Jeep ratios for the TJ's are 3.07, 3.73, 4:10 Pretty easy to determine which one you got
+1 Heck of alot easier than counting the teeth. Put a peice of tape on the tire and one on the d/s for reference points. If the d/s turns a little more than 4 times its 4.10's. Little less, its 3.73's, and you get the picture. The tag on the diff is only good if it has stock gears still in it. My Stang still has the 3.27 tag on it, and it has 3.73's.