Rear end going ouy
There should be a metal tag, held in place by by one of the bolts securing the differential cover. Numbers will identify the rear end. There are also numbers stamped on the axel tube.
I want to say that I remember being able to get that info by decoding the VIN number too.
There were options. You probably have the 9.75" axle.
What is going out? Those are beefy axles. Mine went 185,000 miles until I needed new wheel bearings but the diff looked like brand new.
Looking for a Used F-150 in your area?
CarGurus has 11,434 nationwide F-150 listings starting at $2,700.
Search Ford F-150 Questions
Ford F-150 Experts
Related Models For Sale
Used Cars for Sale