Gents,

I've got a few questions with respect to Ford 9" and 9 3/8" differentials, and I was wondering if you could be so kind as to give me some insight. I've picked up a used 9 3/8" diff centre with 3.5 gears, 31 splines and a limited slip diff. The 9 3/8" differentials came in some 1971-75 Fords and Lincolns.

The ring gear is 9 3/8", not 9" and the carrier is slightly larger than the 9" carrier. The diff housing and axles are interchangable with standard 9" components. You can put a 9" in a 9 3/8" housing just fine, but you will need to grind a 9" housing for ring gear clearance to put a 9 3/8" in a 9" housing. I have read that the 9 3/8" third members were all cast from nodular iron and are stronger than any factory 9" third member.

I would like to exchange the diff with a Detroit Locker and am wondering if you knew what the ring gear register diameter and bolt pattern circle diameters on a standard Ford 9" diff were? From what I've gathered, these dimensions are the same for all Ford 8", 8.8" and 9" diffs, but I have not found any info on whether or not they are also similar to the 9 3/8" diffs.

I would like to find out what custom machine work needs to be done if I wanted to exchange that 9 3/8" diff centre with a Detroit locker (31 spline Ford 9").

 

Here some pictures of the 9 3/8" diff center:

 

Here an image comparing a Ford 9" carrier (limited slip, left) with a Ford 9 3/8" carrier (also limited slip, right). There is a small chance that the bolt circle diameter is the same on both units - if that is indeed the case one can use any 9" diff centre in a 9 3/8" diff. Of course, one would have to make a spacer for centering the larger 9 3/8" ring gear on the 9" diff center.