Guys,

I traded my 2 door JK this past week to a used 2008 stone white 4 door. Is there a letter or number in the vin number that tells what axle ratio the jeep has. Its an automatic, so I am thinking it might be a 3:73 gear. I would like to make sure of what it has so I can determine what mods I want to add first.
Any ideas?

 

Give the VIN to the dealer and they can run a build sheet for you. The jeep web site has a page where you can send in your VIN and they will e-mail you a build sheet.
However, the previous owner could have regeared. So....

If you want to know for sure, and remove all doubt, do this:

Chock the front tires, fore and aft.
Put the transmission in neutral.
Emergency brake off.
Jack the left rear tire off the ground.
Put a jack stand under the frame, just in case the jack fails (had to add this).
Put an index mark on the aft end of the drive shaft, visible from the left rear wheel.
Put an index mark on the left rear tire at the 6 o'clock position.
Rotate the left rear tire 2 complete revolutions while counting how many times the index mark on the drive shaft passes its original position.
That number will be your axle ratio.
Remove jackstand and lower jack.
Put transmission in gear and/or apply emergency brake.
Remove chocks.
If you have limited slip, jack up both rear wheels and rotate one revolution, making sure both tires rotate equally.

If the driveshaft rotated almost 3 1/4 turns, you have 3.21
If the driveshaft rotated almost 3 3/4 turns, you have 3.73
If the driveshaft rotated a little over 4 turns, you have 4.10