Squarebody to GMT400 Chassis Swap

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Aiden Clark

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I have a 1979 GMC C15 that both needs a frame and I would like to make a 4x4, so I found a 1997 4x4 to frame swap with. Does anyone know the cab and bed frame hight difference, and possibly where I could buy mounts since the GMT400 frame is wider than the Squarebody frame? I plan to use the 1997’s 350 and 5-speed transmission, but just do a simple body swap and harness adjustment, and any other advice would be greatly appreciated.
 
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Seen the swaps go the other way (especially with pullin' trucks) but not this way. I always figured there was enough SB frames still out there.

This sounds kind of cool though if you can pull it off.

Oh.....and welcome to our e-lodge. We like pics (and cake).

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TotalyHucked

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I haven't seen that one done with an OBS, only with NBS trucks. There's nothing "simple" about it, it's a TON of work. You'll have to fab up mounts both on the cab and frame side, you'll also have to figure out how to integrate the OBS harness since those trucks are IFS with actuators and whatnot. There's frame height, width and length differences. First thing would be to see how different the wheelbase is.
 
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TotalyHucked said:
I haven't seen that one done with an OBS, only with NBS trucks. There's nothing "simple" about it, it's a TON of work. You'll have to fab up mounts both on the cab and frame side, you'll also have to figure out how to integrate the OBS harness since those trucks are IFS with actuators and whatnot. There's frame height, width and length differences. First thing would be to see how different the wheelbase is.
Click to expand...
The reason I decided for the GMT400 platform is because of the same 131.5 wheelbase and both have the same 8 lug pattern, so I could keep the same length. But I suppose it’ll definitely be a simply said type of swap.
 
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Doppleganger said:
Seen the swaps go the other way (especially with pullin' trucks) but not this way. I always figured there was enough SB frames still out there.

This sounds kind of cool though if you can pull it off.

Oh.....and welcome to our e-lodge. We like pics (and cake).

You must be registered for see images attach
Click to expand...

"E-Lodge"... I like that term :)
 
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TotalyHucked said:
I haven't seen that one done with an OBS, only with NBS trucks. There's nothing "simple" about it, it's a TON of work. You'll have to fab up mounts both on the cab and frame side, you'll also have to figure out how to integrate the OBS harness since those trucks are IFS with actuators and whatnot. There's frame height, width and length differences. First thing would be to see how different the wheelbase is.
Click to expand...
^^^^ This

Sounds like a big job but would be cool to see it pulled off well. I’d bet you would need to run a stand alone PCM or swap to the 0411 GM PCM since the BCM from the GMT400 probably wouldn’t fit anywhere and the old black box computers are a PIA to get programmed

Just trying to integrate the 5.7 Vortec’s air box into my square was a task

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Aren't GMT400 frames wider than a squarebody by a good margin? I know people have put squarebody cab/beds on 2nd gen dodge frames.
 
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legopnuematic said:
Aren't GMT400 frames wider than a squarebody by a good margin? I know people have put squarebody cab/beds on 2nd gen dodge frames.
Click to expand...
Yep, quite a bit. GMT400 is when the fuel tank went inside the frame rails, so they're at least wider by the width of a fuel tank on each side.
 
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TotalyHucked said:
Yep, quite a bit. GMT400 is when the fuel tank went inside the frame rails, so they're at least wider by the width of a fuel tank on each side.
Click to expand...
Only wider by about one tank width since GMT400 only has one tank on DS.
 
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CalSgt said:
^^^^ This

Sounds like a big job but would be cool to see it pulled off well. I’d bet you would need to run a stand alone PCM or swap to the 0411 GM PCM since the BCM from the GMT400 probably wouldn’t fit anywhere and the old black box computers are a PIA to get programmed

Just trying to integrate the 5.7 Vortec’s air box into my square was a task

You must be registered for see images attach
Click to expand...
Casey, watched you do this restore, Fabulous!!!!!
 
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TotalyHucked said:
Yep, quite a bit. GMT400 is when the fuel tank went inside the frame rails, so they're at least wider by the width of a fuel tank on each side.
Click to expand...
Then it's just a tank relocation to inside the rails and some self tappers
 
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