I have an 08 FX4 Screw and I need to know what rear axle I have. I think it is the 9.75" but how can I be sure?

Also, anybody know of a locking diff. for the 9.75"?

 

all 5.4's came factory equipped w/ the 9.75. all 4.2's and 4.6's came w/ the 8.8

 

There is a tag number on the rear axle housing assy. Similar to something like this for a random example:
S***
3L73 975 ****

The 373 is the gear ratio(3.73 to 1). L means limited slip (posi) The next number is the axle size(either 8.8, or 9.75). Top number is just the build code of the axle.

 

Ok yeah I remember my brother told me the same thing when I had my Bronco. Thanks.

Any suggestions for lockers?