I've got a 9" with 28 spline axles in my 61 uni and want to put 31 spline axles in it. The 9" I recently got from an 84 f150 had larger diameter splined end that won't fit into my posi carrier. What I want to do is get 31 spline axles that will fit my carrier and go into the housing that is in the truck now. I would also like to use the brakes from the 84. Thanks Rich.

 

the 80-86 trucks got a wider track on them than previous F100's. Try out a set of 31 spline axles from a 73-79. They should be the right length as your 61. We did this in my buddy's truck as he got a 31 spline gearset that was the right ratio for him.

 

Here is a link to a page that may help with your axle width delemma
I am sure that all ford nine inch truck rear ends where the same width from 73-90 . Eric
http://www.ridgenet.net/~biesiade/Fordrears.html

 

OK, went to the barn and measured (as close as I could by myself) some 9" F100 rearends. Here is what I came up with. 1966= 61 1/4" long, 1974= 64 1/4" long, and 1982=66 1/2" long. These measurements are outside to outside of the drums and may not be as accurate as if I had someone hold the other end. I will have to check what rearend is in my buddy's truck but he swears that it was a 67-72 housing with 73-79 31 spline axles.

 

Thanks guys FYI the rearend in my truck is 64.5" drum to drum and the 84 is 66.5"D/D but I think the housing is the same width it just has wider brakes I'm not sure because I haven't actually measured both. Also the axle shafts from the 84 are equal length and have tapered bearings. Rich