Cab swap info

[Riders2015]

Iv got an 84 GMC high Sierra. I'd like to swap the cab for one off of an 85 Chevy. My main concern is If the mounts and everything else will line up alright. And also would appreciate some tips and tricks for doing this kind of thing. Thank you.

 

[1987 GMC Jimmy]

Iv got an 84 GMC high Sierra. I'd like to swap the cab for one off of an 85 Chevy. My main concern is If the mounts and everything else will line up alright. And also would appreciate some tips and tricks for doing this kind of thing. Thank you.

If they're both C-cabs or K-cabs, then everything's gonna be identical. If not, there's gonna be a difference in the trans hump. It's a pretty straightforward ordeal. Do you know everything you have to remove in order to make it happen? Also, do you know where the truck will stand legally after the cab swap pertaining to titling? That's important. Be careful with the cab bolts or with anything else breaking. Just be patient and take your time so you can put everything back together easily instead of having to wrangle with broken pieces. If you're battling rust, you might and we'll go ahead and clean up anything that would be inaccessible after the swap. Finally, be safe throughout the process. I know this is pretty generic advice, but if you know everything you have to undo for it, you're good to get started.

 

[Riders2015]

The gmc is a 4x4 and the chevy is not. My gmc is a 4 speed. The chevy isn't but I can convert that can't I? I'm doing the swap because my gmc is so rusted. The chevy cab is clean in and out.

 

[HotRodPC]

Yep, You can cut the trans hump out of the GMC and weld it or make it bolt in to the Chevy cab. To be politically correct, cuz you know that's important these days, you'll want to change your badging. And whatever your state laws are on the VIN plate. Otherwise it'll all be bolt in.

One thing I have learned here this week, is the 84 and 85 fuseblock is different. Shouldn't matter though so long you use the 85 underhood engine bay harness too.

 

[75gmck25]

In the older square body trucks there was a bolt-in transmission hump that was different for 2WD and 4WD, however, I think they started using a single piece pan on the mid eighties trucks. You may be able to buy just the bolt-in hump from an older cab and bolt it in over the hole you cut in the 2WD cab.

Bruce

 

[chengny]

The gmc is a 4x4 and the chevy is not. My gmc is a 4 speed. The chevy isn't but I can convert that can't I? I'm doing the swap because my gmc is so rusted. The chevy cab is clean in and out.

You might want to standby and see what happens on this aspect of the switch. I am just about ready to drop an 87 C cab onto an 86 K30 frame. We are going to try mounting it without modifying the C-style tunnel - or changing it to a K-style.

The K30 drive train is a standard 350/TH400/NP205 setup. And - from what I've been able to measure - even with the reduced height of a C tunnel, there should be sufficient room to provide clearance everywhere.

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But as always, the devil is in the details...so we'll see what actually happens. If the tunnel is just a bit too close (or actually impacts the TC), the plan is to shim - as little as necessary - in way of the cab mounts.

The frame is in the shop for sandblasting and epoxy coating as of last week. The cab and all the other body parts are painted and ready to assemble.

 

[HotRodPC]

But a K30 frame is taller/deeper right? So wouldn't that make everything sit a little lower than a 1/2 and 3/4 ton?

 

[chengny]

But a K30 frame is taller/deeper right? So wouldn't that make everything sit a little lower than a 1/2 and 3/4 ton?

I didn't realize the web section of the frame rails on a one ton are taller (from bottom to top flange) than on the 10's & 20's - if that's what you mean. Like this:

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But, since the x-members that support the driveline components are mounted to the lower flange, the additional height of the K30 webs shouldn't have any effect on the vertical position of the components?


But, if nothing else, that additional height in the rail web should set the cab mounts up just a bit higher - and provide more clearance above the driveline components.

 

[smoothandlow84]

When i swapped my 87 cab onto my 84 frame..it was simple and straightforward. I also swapped the dual tamks, motor (originally had a 305, swapped in a 350) as well as the 700r4. Both trucks were 2 wheel drive. The only hang up was no longer having a floor mounted high beam switch and adding the cruise control. Both of these electricl issues were easy fixes. Be sure to soak the cab mounting hardare especially if your donor is from the rust belt area. Be ready to cut or torch mounting hardware as needed.


....and as stated before...check the legality of swapping vin plates with your motor vehicle department first to eliminate headaches.

 

[Craig 85]

You might want to standby and see what happens on this aspect of the switch. I am just about ready to drop an 87 C cab onto an 86 K30 frame. We are going to try mounting it without modifying the C-style tunnel - or changing it to a K-style.

The K30 drive train is a standard 350/TH400/NP205 setup. And - from what I've been able to measure - even with the reduced height of a C tunnel, there should be sufficient room to provide clearance everywhere.

You must be registered for see images attach

You must be registered for see images attach

But as always, the devil is in the details...so we'll see what actually happens. If the tunnel is just a bit too close (or actually impacts the TC), the plan is to shim - as little as necessary - in way of the cab mounts.

The frame is in the shop for sandblasting and epoxy coating as of last week. The cab and all the other body parts are painted and ready to assemble.

ORD makes a 1" body lift if it doesn't fit.

http://www.offroaddesign.com/catalog/oneinchlift.htm

 

[chengny]

ORD makes a 1" body lift if it doesn't fit.

http://www.offroaddesign.com/catalog/oneinchlift.htm

That's what I plan to use - if necessary.