Hear me out...GMT400 box on a square frame

Some of you are probably rolling your eyes (Grit dog I see you lol) But I going to be removing the good things from my old C1500 (1996 C1500 silverado trim) including the Vortec and the 4l60e (I even have an extra 4l60e for it)
Of the things left after removing that stuff, I want to make a truck bed trailer from the box and rear frame, because its in good enough shape. However, its got a 3.73 open 10 bolt, and the large capacity gas tank for the gmt400s, and Id rather not make a trailer that I need to then swap in different parts to make use of those good parts

I want to use the bed for my truck bed trailer which I use for garbage hauling, you all may have seen me talk about it. Its sitting on a 1976 C20 rear frame. If I free up the bed on it, and put a gmt400 bed on it, I dont have to make another trailer that I frankly dont need that much, but I can make use of the bed liner (plastic) and thats its a beat up bed already, and put it to good use for my garbage needs. plastic liner will allow the contents to slip out easily, helping me with when I take it in.

Is it fairly simple to put the box onto the square frame?

If i researched right, this is a gmt400 frame in the rear

Other than the notch for lowering, this is a square body frame
They should both be long bed frames.

It appears the gmt400 uses a flatter frame than a square, and they use hidden fasteners not visible from the top (Not sure how they do it)
But if anyone knows if its easy enough or not, let me know. I have a lot of time to do anything, no time crunch

I'd weld or bolt square tubing or C channel crosswisee on the square frame position it front to rear so it will hit the gmt400 bed mount position holes,and drill holes in the channel/square tubing to bolt the bed down. You may have to make shims to level the bed to the frame. Real ghetto,bolt 4x4s across the square frame,drill holes through the gmt bed, bolt the bed down with carriage bolts.

Ricko1966 said:

I'd weld or bolt square tubing or C channel crosswisee on the square frame position it front to rear so it will hit the gmt400 bed mount position holes,and drill holes in the channel/square tubing to bolt the bed down. You may have to make shims to level the bed to the frame. Real ghetto,bolt 4x4s across the square frame,drill holes through the gmt bed, bolt the bed down with carriage bolts.

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Front to rear would have it the tubing parrallel to the frame, tho, wouldnt it? Wouldnt I want it across so then I could attach to the frame? of course, I would be basically just centering where the wheels sit, it doesnt have a bumper nor will it, so its just a matter of "fore and aft" it needs to be lol

And we're off......

AuroraGirl said:

Front to rear would have it the tubing parrallel to the frame, tho, wouldnt it? Wouldnt I want it across so then I could attach to the frame? of course, I would be basically just centering where the wheels sit, it doesnt have a bumper nor will it, so its just a matter of "fore and aft" it needs to be lol

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Crosswise just like the bumpers seats windshield. But positioned far enough front to back to line up the GMT mounting holes.

SquareRoot said:

And we're off......

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You know it

Im an ameri-can not an Ameri-can't

And dont judge, Ive saved over 40$ a month for the last 5 years by hauling my own garbage instead of paying for pickup from the township

May seem ghetto to a city slicker but I like to work with what I have, and what I have is a gmt400 I got for cheap at auction in 2019, gifted to my dad, he used heavily for 2.5 years, and now is time to make a new home for the saveable/good parts from it and scrap the rest. IF the frame and the body had less rot esp where the mounts were, it would be worth saving a whole vehicle. But the body/cab in the back by where driver sits was already rigged once by my dad in order to level the cab , but its rot city. The frame is a gmt400 which are unfortunately known for rot on the rear portions

ANd the frame by the front control arms has seen better days

But its silverado interior bits , doors, glass, Engine, trans(as a core), axle, etc.. they arent done yet lol.

I look at it as a bonus too, I have the engine which was a rather healthy higher mileage vortec with the original PCM and engine controls entirely mounted in the engine bay, makes it a quick conversion if I desire to keep the factory PCM but its easily converted to something else, and its another SBC I have in my hand.

Which albeit includes 6 SBC's already(counting the one in the 1980 GMC), but of those 6, only 4 appear to be sound mechanically (The 1972 400, the 1967 283, the 1982 305, and the 1978 ish 350 in the truck)

Vs the 1996 roller 350 I already know runs well , as opposed to the unknown running condition SBCs i also have

I shouldnt be so quick to justify myself , but I like to think about it as sharing my joy and future project

On the topic of square, Im going to make some room in my shed to bring the square in out of the outside, because I Want to replace the transfer case mount and then the fuel pump. We have a neighbor plow our snow in the winter, but hes bad about leaving big mounds close to where we park/ the house/etc, And my polaris ranger with a plow is no match for a wet pile of snow that refroze at all, so I think with a replaced tcase mount, a fixed fuel pump (So im not pouring gas in the oil while it runs) , an oil change, and maybe another radiator (to fix the overflow, and a new shroud) and Its going to see light plow use simply to bust those big mounds. The engine mounts will/should wait, but if I have to do them i have spare cups, and would prob just get poly inserts for the mounts

Idc if you didnt read that, because it was more or less my own laying out strategy so it doesnt require anyone else to read it to validate it

Ricko1966 said:

Crosswise just like the bumpers seats windshield. But positionedfront to back to line up the GMT mounting holes.

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Oh I see now

I'm not judging. I admire ingenuity and perseverance.

SquareRoot said:

I'm not judging. I admire ingenuity and perseverance.

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Aww thats awesome , plus i know you usually just are playing around <3

I just wish that rust wasnt the natural state of iron and steel esp in a environment with salt and water lol...

The gmt800 when the bed comes off for a crossmember replacement, im gonna Coal tar epoxy that sucker...

Thoughts on best way to remove frame rust, either with like grinders and the accompanying wheels or sand blasting but at a loss (because not in a cabinet, im assuming thats considered total loss?)
I already improved upon things considerably when I electric-pressure washed the frame and removed what I thought was rust but was just dirt caked on , wasnt rusting it badly but it sat on the outside of the rust and made the rust look 2x as bad. And this electric pressure washer is like home improvement store circa 1988 so its not like a serious gas powered one lol..

I say coal tar epoxy because after learning about it, it is legal to purchase here

I would need to use a mask tho, apparently its some nasty nasty stuff..

Measure the width of the frame. I know the GMT800 has a wider frame than a square. Not sure about the GMT400. So you would need to make some offset brackets.

@bucket you and anyone else with gmt400 could consider this to be an official "part out" if you are interested in any 1996 truck parts. The dash and interior iirc are different 96+ compared to the previous few years, but if there was anything youd like from it feel free to say
I only have jumped on this because my dad, in his complacency, has had someone stealing underhood parts off it and hasnt cared... kinda pissed me off, but its why I want to do something before i find out someones "walked" away with my engine

The washer fluid reservoir, as an example, changed from TBI to Vortec and the 1995 is a 1 gallon reservoir on the fender, but the 1996 is a 1.5 gallon (IIRC) and its also more stealthy and down by the core support with a neck up to where the radiator hose is, thereabouts, , which may be an upgrade but it has a bracket that im guessing is needed with it. Anyone else that has a desire for some part, is an open invitiation.

Turbo4whl said:

Measure the width of the frame. I know the GMT800 has a wider frame than a square. Not sure about the GMT400. So you would need to make some offset brackets.

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Assuming the places the gmt400 bed is bolted is at the cross member spots of the bed, one could just drive a carriage bolt through the "inner" portions maybe? I am supposing a lot by asking that lol...
Since it has a bed liner, I wouldnt care about making exposed bolt heads in the bed, but if I make the right brackets i could easily bolt it the way it is factory as well

AuroraGirl said:

Assuming the places the gmt400 bed is bolted is at the cross member spots of the bed, one could just drive a carriage bolt through the "inner" portions maybe? I am supposing a lot by asking that lol...
Since it has a bed liner, I wouldnt care about making exposed bolt heads in the bed, but if I make the right brackets i could easily bolt it the way it is factory as well

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The reason I said run material crosswise was to make up for the difference in widths,your cross pieces will have to be wider than the gmt mount locations . I figured that light bulb would go off with everyone when I said run cross slats bolted to the square positioned to mount the gmt. I guess it wasn't as clear as I thought. Your cross pieces are going to over hang the sides of the square frame enough to bolt the GMT bed to them.

Ricko1966 said:

The reason I said run material crosswise was to make up for the difference in widths,your cross pieces will have to be wider than the gmt mount locations . I figured that light bulb would go off with everyone when I said run cross slats bolted to the square positioned to mount the gmt. I guess it wasn't as clear as I thought. Your cross pieces are going to over hang the sides of the square frame enough to bolt the GMT bed to them.

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Gotcha, thanks for clarifying, I had you opposite in one way, and the reason for saying it an entire different way lol. Appreciate it. So it seems like basic bracket-ing could make the swap doable, I have the metal to do the job, and either get my stick welder going or have my dad bring his and maybe bolt things together, but use the opportunity to put some welds down after some practice. Then get judged by the internet for the quality of them (joking lol)

The gmt400 bed is slighly bowed outwards if you look at it from the rear straight on, because of the heavy toolboxes my dad used on it. Good time to bracket it and tug it back to proper assuming the bed floor support isnt just shot (like on my current trailer bed)
Also good use for the bed, I think it was one of the least pleasant greens GM has used on a vehicle lol.