How would you do this? BTW thanks for the help.
Using this method assumed the axles and bearings are in decent shape and not froze up. Consider this a guesstimate method only but it will get you close. Always best to open them up and verify. It would really suck to buy two axles and find out one is a 3.73 and the other a 3.54.
I bought some axles off craigslist that sat in a field for years. Best I could tell were 3.73's in the 2 dana 30s, a 2.73 in one 20 and I thought the other 20 had 3.73's. Turned out it had 3.54's
. Even if I had known the 20 had 3.54's, I still would have bought them because I needed various parts from both 20's, Backing plates were good on the 2.73 and the 3.54 carrier to replace my original 2.73 carrier so I can change Ring gear to 3.73. New 3.73 R&P and Superior Axles came in yesterday, but still waiting on the installation kit.
This link will help. Good luck.
Posted from Jedi.com; What's My Gear Ratio?
So, assuming you've got an axle up in the air with the driveshaft disconnected & neither wheel on the ground:
* If you turn one tire & the other one either stays still while the pinion rotates, or the other one rotates backward while the pinion stays still, or something in between, then you've got an open diff or a very weak LSD (like a Trac-Lok with too many miles on it). In this case, you need to secure one wheel (perhaps by lowering the tire onto the ground), then you can figure your gear ratio by rotating the airborne tire TWO full rotations and counting the number of times the pinion rotates. 3.73 turns means 3.73 gears. If you only rotate the tire once, then 1.865 turns means 3.73 gears.
* If you turn one tire & the other one turns the same number of turns in the same direction, then you've got a good LSD or locker. In this case, you can just rotate the tires ONE full rotation and figure your gear ratio by counting the number of times your pinion rotates. 3.73 turns means 3.73 gears.