Supachop

I bought a pre-owned 2009 Wrangler X. How can I determine the factory diff gear ratio?

weebus

i think you can call the dealer and give them vin and/or axle code and they should be able to tell you. or you could get a paint stick/chalk jack up rear put on stands for saftey! draw straight line on driveshaft put a a line on a rear tire and in neutral turn the drive shaft one full turn and count the times the tire goes around should get you very close like 3 1/4 turns would be 3.73

weebus

3 1/4 would be 3.21 lol 3 3/4 would be 3.73 my bad

ronjenx

A build sheet will tell you what it left the factory with.
If you want to know what your used vehicle has...
Here is an outline on how to do it:

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 jack stand and lower jack.
Put transmission in gear or Park, 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 drive shaft rotated almost 3¼ turns, you have 3.21
If the drive shaft rotated almost 3¾ turns, you have 3.73
If the drive shaft rotated a little over 4 turns, you have 4.10
If the drive shaft rotated 4½ turns, you have 4.56
If the drive shaft rotated a little under 5 turns, you have 4.88
If the drive shaft rotated a little over 5 turns, you have 5.13