Cab swap: 99 Reg 6.5 cab onto 97 Ext 454

[Miles B]

Hi

I've got a 97 4WD ECLB that has the 454 gas motor. The drivetrain/chassis is A1 but the body is trash.

I always wanted a regular cab. The ext cab makes the truck too long over here. I'm perfectly fine cutting the chassis, I know how to do that. I'm looking at buying a really nice condition regular cab '99 2WD 6.5 TD 3500.. these were brought over here to make into ambulances, they're still the GMT400 style. The body is great but the diesel is tired and I want my 4WD. My 454 drivetrain is perfect.

I know I'll need to swap the instrument cluster. Looking in my '97 service manual I don't see any obvious differences in the main harness that goes from cab to engine bay.

Does anyone know of anything else that could go wrong? Thanks!!

 

[someotherguy]

A lot can go wrong! But what you want to do is possible, with probably a couple big gotchas, and of course many small ones.

Biggest gotcha: you want 4WD but you're using a 2WD chassis. There's no way to mount up your front diff, torsion bars, etc. so as far as I can guess, your only option here would be to do a solid axle swap (SAS) so that's some more parts hunting. It'll be stronger than the factory 4WD IFS setup, so that's a plus.

Fuel line and sender differences but you can just swap your pieces over and chop them up as needed. Harness along the frame to the sender will be different as well as the pump setup between diesel and gas differ.

There are some electrical changes in the '99 GMT400, as well as differences between diesel and gas, that would make me want to swap the dash harness just to be 100% sure. It's no fun pulling the 95-up dash so I'd do it once to swap the harness, and be done.

A little nibbling on the cab floor to install your 4WD shifter will be needed but you can easily use your old cab as an example.

If you intend to swap your seat into the reg cab it'll need a little bracket work on the inside brackets as the extended cab floor profile is different than the regular cab. Again, no big deal.

Richard

 

[Miles B]

Hi

I just want to pick up the diesel regular cab and put it onto the 4wd 454 chassis. I'm most interested in if there's any difference in wiring between diesel and gas cabs. So far I looked at the wiring diagrams in my 97 service manual and have just seen the one big harness connector but no notes about different versions for diesel. Any idea what might be different in the harness? I'll keep looking and see if I can dig up a 99 manual too.

 

[Miles B]

I've spent some time looking at the 97 and 98 manuals. It seems the harness going from the cab to the engine bay is the same.

As you say, there is a difference in the dash harnesses. The diesel has the PCM under the dash, the gas has its computer under the hood. C200 is the big connector from the diesel PCM to the cluster. That's different. So it would need at least some of the gas dash harness.

It also looks like the diesel throttle pedal is different. I'm guessing it's DBW.

Compounding all of my problems is these trucks have been RHD converted.. so it's not a simple matter of pulling the harness and swapping it over. Who knows what has been cut...