Does anyone have first-hand knowledge whether a 9" third member from a '78 will fit in the housing of a '71? I sold a guy my '78 rear end, and it's too wide for his '71, and we wondered if he could swap the guts?
I'm not a axle guru so I need some help here...

Thanks,
Brad

 

As long as the axle spline count is the same, it should. The 78 will be 31 spline I believe.
There may be different yokes on each too, possibly for different sized u-joints, and yoke lengths.

 

The spline count depends on the model of truck. I think 2wd had 28 splines and the 4x4's had the 31'splines. At least thats how my 2 trucks were. My 2wd was a F-100 though, not a F-150, so that may have something to do with the spline count also. They were both 1978's. I'm sure someone else on here knows for sure.

 

you could always move the spring perches to match up. the rear end on the 71 is narrower then the front track width. if you use the 78 they will be the same.