73-79 frames the same

[71Ford100]

I was wondering if a 73-79 frame was the same more imporatntly 76-79, grandpa said didn't wan't 73-75 4x4 for some reason. I wan't to in the future convert my 71 4x2 into 4x4 and there are alot of 76-79 4x4s around.

[willowbilly3]

The wheelbase is 2 inches longer and you have to deal with that issue. If it is an F-100 4x4 I think the frame is wider in the back. The F-250 4x4 (through mid 77) uses the same frame width as the 72 and older trucks. I would almost bet Keith has a tech article expounding on the frame dismensions.

[FORDification]

I don't have an article on this, but based on the number of people who keep asking me this (normally via e-mail) I think maybe it's about time I added one.

With one exception, the '73-'79 trucks frames were all the same on the front half (so the cab and front clip bolt right up) but the rear half of the frame was 4" wider, which simply means you'd have to drill new bed mounting holes. As willowbilly mentioned, these frames were also a bit longer, meaning that if you center the rear wheelwells over the rear tires, the gap between the cab and box is going to be a little wider.

The one exception is the '73 thru '77-1/2 F250 4WD frames were still narrow in the back, so the box should bolt right up, but the frame is still longer, so the cab-to-box gap will still be increased with the box centered over the rear tires.

[willowbilly3]

Keith, I must add my one and only experience doing a body swap was to put a 72 F-100 2wd body to a 76 F-150 4x4 frame. Here is how we did the bed. We split the difference and pulled it back an extra inch and lived with the wheels being an inch off center of the wheel opening. But I don't think you could just drill new holes without reinforcing them. If you notice the holes in the bed have a sleeve in them so the carriage bolt head isn't just pulling against the tin in the bed floor. Without that sleeve I think the bolts would just suck into the bed. Here is what I did. I cut some sections of medium wall square tubing (seems like 1 1/2 inch) to just snugly fit inside the frame and drilled the holes in them. When the bolts were tightened it clamps against the top lip of the frame rail. At this point you could weld them in place but I never. I only used two (that was all the square tube we had and never got around to doing any more). I did weld some strap to the back for the two short bolts so the bed wouldn't tend to slide back and forth.
Also note that we had to whittle up the left front inner fender to clear the F-150 power steering box. And neither speedometer cable would work. And the geometry was all wrong on the column shifter, both trucks were C6. I had to do some modifications underneath to get all the gears indexed to the detents in the column.

['75-4x4guy]

I dont have any experence between the 67-72 to 73-79 swaps but I have swaped quite a few beds and other body parts on the 73-79 F100/F150 4X4's
I have found that the f100/150s are pretty much all the same when it comes to the chassis . I have to agree with 71ford100's grandpa in that the 73-75 f100s are not a good swap in that they have a pretty lame steering system and repalcement parts are very expencive ( when you can find them)
They also have drum brakes in the front while this is not really THAT bad some people just dont care for them .
I have them on my truck and they seem to work ok for me . (1975 4x4 F100)
I have also heard that the 73-76 trucks use a low pinion differential which is considered by some to be weak .
My truck has a factory high pinion differential .
I think that if you can only find a 73-75 truck then there is nothing wrong with using it in your swap.
One other point to keep in mind is engine perches , while this isnt anything earth shattering keep in mind that after 1976 for went to the 351m/400 which uses different engine perches in the inline six / FE, so this wont be a drop in if you are planning on using you original running gear . There are also other items but with a little planning and of course help for people here it is do-able .