Hello all-wise forum. Question, is there a difference between the front axle on a 56 F-100 and a 51 F-1? The reason I ask is that I saw a dropped axle advertised cheap, but it was for a 56 (according to the ad)... but maybe they're interchangeable? Thank you.

 

The spring mounting pads are set further apart on the 53 and later trucks - it is about a
2" difference

 

They are totally different and not interchangable. For starters, the spring pad locations are wider on the later trucks. The spindles and king pins don't interchange, either. Ford made quite a few changes up front in '53.

 

They are very much different in every way. I have all the measurement and pics for all the Ford straight axles on my web site Dropped axle Axles Axel this should help you out.