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Changing a cab
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Post Changing a cab 
It's been a while....sorry. I have 2 2wd the body on my 98xcab is mint but the frame and drive train notsomuch. ..the other is a 97xcab with a great frame and drivetrain. My question is how hard is it to swap cabs. ....1 truck is a 305 the other a 350. Is it as simple as nuts and bolt etc and plugging in the computer from 1 truck to the other?
Thks for any input
Lorne

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Are the wire harness the same? I think not. Might have to swap the 98 frame wires to the 97 frame.

Never done it, but from what I see on car shows, pretty much nuts and bolt etc IF the frame bolting points are the same.

Isn't it how the manufacturer assembles them in the first place?

If you have a lift and make sure you disconnect everything as you slowly lift it doable.

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Lots of nuts and bolts but in the grand scheme of things it is plug and play. The wire harness are similar but different. The 98 has the fuel gauge go through the PCM where as the 97 does not. Personally I would leave as much intact on the 98 and swap that to the 97 frame. The engine sensors are all the same. The only thing that may be different is the EVAP stuff only because the displacement of engine differences. Many people are doing this to these trucks that are in the "rust belt."

TJ

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Your biggest challenge will be the actual swap, not the nitpicky things like wiring and all. The cab is heavy, and you will not want to just put a strap through the doors to pick it up. The beds will need to come off first, and I recommend using 4x4s under the cab at the cab mount points to actually pick it up. I would also bolt the cab to the 4x4s to ensure it doesn't slide off while moving it. A jack, a bunch of concrete blocks and time is all you need after that. Connect the long 4x4s with shorter ones, then jack one side at a time.

This is also a good time for new frame mounts all around and I'd replace all of them, not just the cab mounts to make sure the body lines all line up correctly. This is also a good time to get some underbody rustproofing. Get the good professional stuff from the automotive paint store, not the parts store garbage.

Careful though, this can easily turn into a 2-3 year project. Just in the 5 minutes since I first saw this post I thought of a half dozen things that can be done while the cab is off the frame. Some things I wanted to do to my S10 when I was working to make it my own was put in an in-bed tool/security box and move the battery under the bed. Was going to build a manual drop shelf that would let me swing the battery down from underneath by hand when I wanted, with push pins to keep it in place while on the road. I never figured out exactly how to do it but I also wanted to put a spare tire mount that would set the tire upright but out of the way. Since I almost never used it to move heavy stuff my intent was to move it to more of a 50/50 weight balance. Also, if you are an audio guy we all know how hard it is to find a place to stick the gear in a truck. This is a good time to enlarge the cab area where needed to make room for subwoofers and amplifiers. If you don't mind losing a bit of bed space you can build a shelf into the back of the cab to make room for the gear, then put a matching cut-in into the bed to make room for the cab shelf. It would be almost completely invisible to the outside world once the truck was put back together.

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Thanks for the replies. ...I have a forklift so the lifting part is easy. If the pcm is different then I need 1 from a 98 with a 350 in it or can I keep the complete harness from the 97?

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I think 97 to 98 was a major changeover in the GMT400s, so you'll want to keep the PCM with the wiring harness you use. However, and someone else will need to check me on this, the PCM hardware may actually be identical for both years so you may just need to get your PCM flashed to match the harness you use. Of course, you also need all the electronics that go with that harness too.

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My dream is to do just that, except go from my half ton frame to a 3/4 ton since the 3/4 ton never come with a third door. Then I will have the heavier front diff and get the full floater in the back. I actually helped change a cab on a smaller Mack truck. Had to do some wiring swaps too. We had an over head lift that had two chain lifts on it. We did run a strap through but we had two lifts so it wasn't being pulled together, other wise you would need a spreader bar so you would pick up on both sides with out crushing the middle of the cab. For that job, just like on the shows a shop hoist would work wonders. Then you could just pick up the cab roll out one chassis and roll in the other. I know I don't have access to one.

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