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Username Post: Body swap questions        (Topic#289297)
hhelfenb2 
Forum Newbie
Posts: 4

Age: 52
Loc: Phoenix, Arizona
Reg: 11-07-12
11-07-12 07:34 PM - Post#2287074    

I want to swap the body (front end/cab/bed) from my '78 GMC Sierra Grande DIESEL pickup to my '78 GMC 3/4 ton 4x4 pickup. I know I need to cut a hole in the floor where my transfer case lever comes thru and also put an extra gas tank opening on the other pickup too, but what else will I need to do to get the DIESEL body on the gasser? I am wondering about how to do the electrical connection and also go from a body (cab) with A/C to a truck/engine without A/C (I want the A/C to work on my 4x4 when all done with the swap. Has anyone done this before?? Any suggestions or words of advise? THANK YOU!
1978 GMC Sierra 3/4 ton 350-V8 4x4 pickup and
1978 GMC Sierra Grande 1/2 ton 350DX diesel pickup


 
beagrizzly 
"2nd Year" Silver Supporting Member
Posts: 1648
beagrizzly
Age: 64
Loc: south texas
Reg: 08-04-12
11-07-12 09:10 PM - Post#2287114    
    In response to hhelfenb2

i have, and the mods and problems over come are way too numerous to cover in this forum.
i do have some advice.................run, Forest, Run!!

 
hhelfenb2 
Forum Newbie
Posts: 4

Age: 52
Loc: Phoenix, Arizona
Reg: 11-07-12
11-07-12 09:31 PM - Post#2287121    
    In response to hhelfenb2

Really? I already purchased the body mount kits from LMC and Jeggs... it's cooler here now in Phoenix so the weather is perfect for working on it now. I don't need either of the cars running soon. What will be the hardest thing to overcome? The A/C stuff? I'm kinda set on doing this. It can't cost that much besides time. Is it really that much easier to just throw a donor gasser motor & trans into the diesel body (new gas tank and fuel lines) and then just buy another front end clip for my 4x4?
1978 GMC Sierra 3/4 ton 350-V8 4x4 pickup and
1978 GMC Sierra Grande 1/2 ton 350DX diesel pickup


 
75gmck25 
Contributor
Posts: 345

Loc: Alexandria, VA
Reg: 12-25-07
11-08-12 03:49 AM - Post#2287164    
    In response to hhelfenb2

I would expect it to be a lot of work (many tasks and many parts to move), but with two vehicles of the same year there should not be many "mods" required.

The biggest body mod that comes to mind is that the hump in the center of the floor on a 4WD is shaped different (higher) than a 2WD. However, on some years that center section is bolted in, so it can also be moved. I don't remember how its mounted on a '78.

Of course your gauge cluster has to match the engine, and there may be some extra wiring on a diesel that is not needed with a gas engine.

Bruce

 
GMBOB 
Senior Member
Posts: 557

Loc: WARREN,MI,USA
Reg: 01-31-01
11-08-12 03:51 AM - Post#2287166    
    In response to hhelfenb2

The cab is easy. I swapped a 1991 crewcab (non A/C) onto a 1986 truck chassis (w/ A/C). The engine you will need brackets. Ask specific questions, I never even discharged my A/C.
31 Chevy 5-Wdo Coupe
55 Chevy
56 Corvette
29 Chevy 2-DR Sedan
86 GMC Crew Cab (500,000+ miles)
90 GMC Suburban


 
Vaughn 
"13th Year" Gold Supporting Member
Posts: 15599

Loc: Colorado Springs, CO
Reg: 08-08-04
11-08-12 12:19 PM - Post#2287298    
    In response to GMBOB

You may have to swap the wiring harness across the trucks, but it isn't that difficult to do.

MOST of the wiring harness will work across the body change, but there are some differences between the diesel and the gas motor version (like the dual battery and the glow plug wiring harness stuff).

 
hhelfenb2 
Forum Newbie
Posts: 4

Age: 52
Loc: Phoenix, Arizona
Reg: 11-07-12
11-08-12 05:49 PM - Post#2287408    
    In response to Vaughn

Can't I just pop the harness off the engine wiring harness from the gasser cab and lable it all and then put it in place of the diesel engine wiring harness? Isn't that big plug a direct fit? Do I have to worry about the wiring inside the diesel cab or just hook up the ignition? Thank you for your replies, all! This is a new one for me and I appreciate it!
1978 GMC Sierra 3/4 ton 350-V8 4x4 pickup and
1978 GMC Sierra Grande 1/2 ton 350DX diesel pickup


 
75gmck25 
Contributor
Posts: 345

Loc: Alexandria, VA
Reg: 12-25-07
11-09-12 03:34 AM - Post#2287514    
    In response to hhelfenb2

In most cases these trucks have a base factory wiring harness that is identical, and extra wiring is added for options. For example the tach cluster just adds a small 3 wire harness, and the dual fuel tanks adds a separate 5-6 wire harness for the switch and additional tank. GM designed the trucks to make it easy to add options while leaving the basic harness the same.

If this is true for the diesel (it just adds more wiring), you will have extra wires you don't need, but the diesel truck will have the same basic harness as the truck with the gas engine.

Bruce

 
GMBOB 
Senior Member
Posts: 557

Loc: WARREN,MI,USA
Reg: 01-31-01
11-09-12 06:10 AM - Post#2287525    
    In response to hhelfenb2

The wiring is different for gauges vs idiot light. It is not difficult to change though. A tilt column wiring is dressed different then a non tilt for a similiar year. The ignition switch connector is 180 degrees different. Can be fixed by removing some tape, and retaping. There may be some differences in wiring for the trans or cruise control. But usually it is a stand alone harness and the firewall has a little indention to aid in locating and drilling a new hole. Going the other way you may have to plug a hole or two.
31 Chevy 5-Wdo Coupe
55 Chevy
56 Corvette
29 Chevy 2-DR Sedan
86 GMC Crew Cab (500,000+ miles)
90 GMC Suburban


 
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