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K5 Frame swap

Jumppr

Jumppr

1/2 ton status
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Location
Clovis, Ca
Can I use a late model frame under a 75 body? I think just the body mounts need to be moved, but how hard is it? Or is it too much trouble? I need a better frame and I’ve seen a few 80’s era K5’s going for $500-800. Figures I could get the whole truck and use what I need and pet the rest out.
 
You dont have to move the body mount brackets. You just have to match the correct bushings.

I can't remember if they have to be matched to the cab or the frame... someone else will know though.
 
The frames are different like @skunked said. I have a 75 tub on an 80s frame. I've got a weird combo of body lift to get the tub level
 
Floors are different on the 76 and down frames. Because of that there is a different location for the body mount behind the front seat area and the cross brace differs.
 
I sold my 75 frame to a buddy who's frame on his CUCV Blazer (85) was bent hard on one rail. It wasn't until he dropped the CUCV body on it, that he saw the difference. He didn't want to fuss with swapping body mounts and such, so he unloaded my frame and found another one (but 77 and up) on craigslist.
 
There were big changes in the floor pan. I think '77 was the last year that the rear deck pan went all the way forward to the back of the driver's and passenger's seats. Starting with '78 there is much more leg room for passengers in the rear. It wasn't so much due to the seats being shifted front or rearward, it was mostly due floor level being lowered to the same elevation as the front of the cab, the passengers in the rear didn't have their feet resting on the rear floor pan level, their feet were now at the same level as the driver and passenger front.

For kids and their height, it didn't make a big difference since their feet wouldn't touch the rear floor area, but it made a big difference for adults sitting in the rear.

Another change made was that the rear bench seat folds and flips forward to allow more cargo space in the rear floor pan. My '77 rear seat is a pain to unbolt and remove if I need more space in the rear. In my '79, I just flip the seat forward!
 
You know I really ought to get off my a$$ and go look. I have a '78 and a '77. I too am thinking on doing a swap. A '77 tub on a '91 frame.
 
Ok so it looks like it would be a lot of work. Here is where the tub differences are that I can tell. This is the '77 which I assume will be same as '75.
IMG_20180728_180456848.jpg
The body mount is directly behind the cab elevation transition directly behind the front seat. It's in an actual crossmember on the inside of the frame rail. The crossmember and suspension are tied together. It's more complicated than my '78 here.
IMG_20180728_180900842.jpg
The '78s body mount is on the outside of the frame rail and stands alone. It's lower due to the foot well for the rear seat. It's 2 1/4" closer to the body mount below the foot well behind the engine fire wall. The suspension shackles are different not tied to body mount it's all much more simplified. Looked at my '91 & it seems to be same as the '78. I suspected the mounts for the core support would be different but they look the same. I know somebody here can correct me if I'm wrong.

We are basically thinking about doing the same thing. If I do it and I probably will. I will remove the crossmember from my '77 and install it in the '91 along with the body mount. It might be a big ol B grinding and cutting all those rivets but there's to much room for error on my part, in my head, in the long run of the swap. Without question going original crossmember/body mount will work. Will have to drill some holes. Hope this helped
 
FWIW, I just put a '90 body on a '79 frame. All went well, considering that I know that both the body and chassis have had some rough treatment in their past.
 
I never thought about removing the body mounts from the old frame and using them on the new one.

Hindsight is 20/20! I sure wish I knew better what to look for when I was buying the POS I have now.
 
That cross member and body mount on the '73 to '77 looks to take up a little real estate. Just a little. Making running the exhaust more challenging.
 
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