Last weekend the rear diff went bad and resulted in a cracked diff housing. I bought a used rear axle but need to know if there's a way to find the ratio and if it has an open diff without the VIN or opening the diff if possible.

My truck is a 2004 1500 4x4 5.7L and the donor is a 2003 1500 4x2 5.7L. At least I think it's 4x2. Both are quad cab SLT with the 20" wheels with the plastic chrome covers.

I have the numbers that are stamped onto the diff housing and one of the plates that's next to the spring perch.

Thanks.

 

There should be a tag, bolted to the diff cover. Pull the cover. Count how many times the pinion gear vs main gear. That will give you gear ratio.

 

Raise the rear on stands, mark the tire at some easy reference point, mark the driveline, rotate the driveline and count the number of turns to make a full revolution of the wheel.
3-1/2=3.55, 3-3/4=3.73, 3 and a lot more than 3/4, but not 4=3.92, over 4=4.10, 4-1/2= 4.56.
Not real exacting, but totally free too.