Aside from the differential covers, the biggest difference between the axles is the size. The number in the name (Dana 30, Dana 44, etc.) is in reference to the sizes of the axle. Dana 30: This axle the front axle most commonly used on all non-Rubicon model TJs.

You can use the VIN to order a free Build Sheet and it will tell you what the gearing was from the Plant. For instance my Build Sheet says "DMFP 4.10 Rear Axle Ratio" Contact Jeep

There are a few ways to determine your axle gear ratio: 1. Look for a tag under one of the diff cover bolts in the 9 o'clock position. This will tell you what ratio the Jeep originally had and likely should still have. If someone would have regeared it, chances are they would not put the tag back on.

Look at the axle tag bolted to the 9 o'clock position of your differential cover, that tag has your ratio stamped into it. This tag is indicating the axle gears inside have a 3.73 ratio. If your axle still has this tag odds are high that it was not regeared and that it still has the same ratio gears the factory installed.