I went to my local yard and they had about 12 different 2wd F100s all 70s w/ rear 9". (No F150s/250s/350s/4x4s) Anyways I noticed most of the 9" I found had the rounded housing, which I guess is 28 spline. But a few (from the top view) were flat and wider, which looks to be hd housing compared to the other. Would it be safe to assume the hd housing 9"s are probably 31 spline? Also what wms to wms are these 9"? I also think I found an early 80s w/ 5 on 4.5 which is perfect for my XJ.

I also have been told to look for an N on the top of the housing, is this true for the F100s?

I didn't have my tape measure or tools w/ me at the time and the yard is over an hour away. So that is why I ask here :D

Thanks

I'm not sure you can be sure about the rounded housings being any certain spline count. I do know that an "N" case was used in F100's,,,most of the time with a factory 460 in them. I have never seen a 9" with that bolt pattern, for the most part every one that I have or have had is 5 on 5.5

80-82 F100's with power brakes have the 5x4.5" pattern. This is a 31 spline, late big bearing axle. 80-86 F-Trucks got one of the strongest housings Ford built.

An "N" case indicates it is nodular, a strong case, and quite preferred. I would look at the HD housings, and pull a shaft and count the splines to be on the safe side. All it takes is removing the 4 nuts from the retaining plate after you pull the brake drum off. I wouldn't assume anything in a stacked pile of axles. Pull the shafts to make sure. And measure the outer housing ends to make sure they are big bearing ends. I think the big bearing end will have a 2.325" measurement from the center to center measurement on the top to bottom retaining bolts, and I think the small bearing ones had a 2" measurement, but I'm not certain.

Check Moser's site, I think they list the dimensions on the retaining plates so you can verify if they are big or small bearing units.

When we put a mini spool in my buddies 74' F-100, it had the smaller housing, 28 spline rearend.