The rear axle on my 71 F100 4x4 is about 4" narrower than the Dana 44 in the front. I put stock 79 Bronco rims on it and it doesnt look right because of the diffrent axle width.All the rims have the same backset, why did Ford build these rearends so much narrower than the front?
My '71 4wd F100 has the same axles you do and my tires ride in almost exactlythe same tracks, did you buy it new? It is very possible that someone changed some thing in the trucks almost 30 year life time. Or maybe somebody fixed mine before I got it. DinosaurFan
The reason the track widths differ from front to rear is for handling. If you look at the older Chevy's and Dodge's, you will notice the difference in axle width. The front is usually wider than the rear. As to what difference the width makes for handling, I do not have an answer, but I have been told by many people that is the reason. Another reason for the front being wider may be to allow for the front tires to turn. The distance from the rear tires to the springs would not allow much of a turning radius.
I just recently replaced the rear axel in my '72 F-100 4X4 as you did & had the same question. Mine was 4" shorter in the rear also. I replaced it with a Ford 9" 31 spline. I noticed its a lot better ride, feels more balanced. And as luck would have it the gears are the same. I got it out of a 74 F-150 4X4.