I'm trying to finish an rear diff swap into my 85. I have a 89, i think not too sure on the year, v6 diff. It has the four ribs and is 3 inches wider than the rear diff I pulled out. Are the u-bolts and mounts different? The newer diff is around an inch wider in diameter than the stock 85 rear axle.

 

*Sigh* have you considered the search function? this has been covered a million times before, and all have concluded that as long as the differential ratio is the same, and the spring perches are the same distance apart. They can be swapped.

 

I don't have the 89's perchers, but thank you old great one.

 

The '89 axle tube is 3" OD vs. 2.5" on the '85 axle. If you'll be using the stock u-bolt setup, you'll need the spring plates and possibly u-bolts off the '89 (depends if they are the narrow or wide spring perch version). If doing a u-bolt flip (u-bolts around the tube), you'll need 3" ID u-bolts and matching spring plates.

 

sounds like the wider dif came from a late model truck or 4 rnr. I have a v6 dif in my '86 and the diameters are the same for the 8" 4cyl and 6cyl.

http://home.4x4wire.com/erik/diffs/ might help.

 

After 85, the rear axle housing got slightly wider to match the IFS track width, and a larger housing.
before 85, the rear axle is like a 2" diameter