Fitment of 81 body parts to 73-80 frame

[Braxton Blakley]

Hey [emoji112], I'm new here and I have a new guy question that's probably been covered a million times

I wrecked my k10 and found a new frame, threw a cummins in it, blah blah, here's my issue as of late:

I mounted my cab/ core support and after I cut bigger holes on the mount pads, I am finding out that 73 to 80 frame yrs had different mount locations/hole sizes...

So I now have 81 style body mounts, and my 81 front clip now sticks out further than my 81 fenders

QUESTION: do I need to find a core support and fenders/hood from a 73 to 80 to fit to my older frame??? And will the body lines line up with my 81 cab and bed??

(Couple pics for attention)

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[PrairieDrifter]

Is the core support bolted to the fender in that picture? The main core support bolts through the frame mounts tight? They will have a lot of back and forth sway just sitting there loose.

The body lines would match if you went to a roundeye front clip. People have done each of these swaps many times, don't remember the frame mounts being an issue.

 

[Braxton Blakley]

In that pic the core support was loose to allow some.movement, but its completely impossible to get it to bolt where it needs to on the fender.

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[AKguy]

My 1981 C20 sheet metal mounted on a 1980 K30 frame required moving the core support holes a bit back.

 

[Braxton Blakley]

My 1981 C20 sheet metal mounted on a 1980 K30 frame required moving the core support holes a bit back.

That's what I was afraid of. I've already purchased my sheet metal, but I don't really have much room to move my core mounts back and still use the cummins mechanical fan. Sucks.

Does a 1981 hood cross over to 1980 body styles or would I need the whole 1980 front clip with a 1980 hood?

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[AKguy]

The hinges changed in 1981 and would likely not bolt onto earlier fenders. Here’sca pic of the original 1980 mount hole and the new hole location prior to cutting.

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[Braxton Blakley]

Hell yea, thanks for the help.

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[Braxton Blakley]

Idk if im allowed to keep posting in this thread, but its related anyway.

So I have popped out the rivets on my core support mount bracket and now I'm moving them back and welding them back on.

Question: after I bolted the core support to the fenders it picked up my core support 1.5" off my body mounts. I had to install a 1" body lift for various reasons, so now it's like 2.5" away from my frame

Should I weld the brackets back on close to stock location, or should I just weld them back on wherever they fit with the body mount/lift spacer installed??

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[Braxton Blakley]

Anybody?

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[PrairieDrifter]

Anybody?

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Are your cab mounts looking ok? The bushings mainly, but the mounts too.

I'd say do whatever you need to get it mounted right. But i would also want it to be "right" depends on your plans with the truck.

 

[Fat 454]

Hi, as you probably know, all the sheet metal from the bulkhead / scuttle forward changed in the 80/81 model year. This included the hood hinges. The scuttle ( cab ) is the same post '81 to pre 81 tho I think, which is why if you change all the sheetmetal ( including core support and hood hinges ) you can swap from pre ( roundeye ) to post ( square lights ). You can't mix and match between the 2 styles tho, so a pre 81 core support won't fit a post 81 fender / hood.
The frames really change as well. I have a pre '76 blazer and the replaced the body with a post '78. The floor / frame is completely different between the 2 ( to allow for the tumble rear seat ). I could have fitted the newer body to the older frame using 2" lift mounts, but found the lift then needed so many other changes ( including but not limited to : steering column, wiring loom, throttle, gearshift, trans shift, etc. etc. basically anything that went through the floor ), so I decided to cut the rear floor of the body to clear the frame instead and keep the body at stock height.
Anyhoo .. the motto of this long story is keeping the body / frame at stock height, with using all new body mounting rubbers to rectify any misalignment, should mean that the core support will line up ok. If it doesn't, you may be dealing with factory assy tolerances ( which can add up ) and / or frame mis alignment. If you have done all this work and swapped the frame, it would be worth taking some diagonal measurements to make sure your "new" frame has not had any mishaps ( I have had some that were off more than 1/4" from the factory ).
Finally, having said all that, if you do use a lift kit and re-locate the brackets I would suggest :
1 - keep the height of the bracket to frame the same ( just move forward / back , not up / down ) so that you don't reduce the size of the mounting area and therefore strength
2 - use grade 8 bolts rather than weld back in ( at least initially ) so that you can move / modify / adjust if required
3 - or you could go "all in" and use bracket relocation and lift to make more clearance for the cummins to the firewall by moving the cab up ( although other conversions I have seen use a high hump and / or mod the firewall - which is what I am looking to do )..re Finnigan's garage ? ..

Hope some / any of this helps ..

 

[Turbo4whl]

Anybody?

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Since you said anybody, this old man will chime in, this might help.

Different year frames for 3/4 ton and 1/2 ton 4 wheel drive require different body mounts. The big difference is the rear cab rubber mounts need to be taller.

Not knowing for sure which year parts you are using, taller rear cab mounts will rock/ align the front core mounts lower. One way to check this, set the rear bed back on the frame and see if the cab is lined up correctly to match the bed.

Example from LMC:

1973-89 Polyurethane Cab Mount Bushing Set​

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Product Details

1973-87 STD CAB 1/2 TON & 3/4 TON 1973-89 CREW3/4TON
	34-0101		BUSHING SET-CAB MOUNT 30PC	2 WHEEL DRIVE 1/2 TON 73-80	1	$79.95	IN STOCK		ADD TO CART
	34-0102		BUSHING SET-CAB MOUNT 20PC	2 WHEEL DRIVE 3/4 TON 73-80	1	$91.95	IN STOCK		ADD TO CART
	34-0102		BUSHING SET-CAB MOUNT 20PC	4 WHEEL DRIVE 73-80	1	$91.95	IN STOCK		ADD TO CART
	34-0108		BUSHING SET-CAB MOUNT 12PC	STANDARD CAB 81-87	1				TEMPORARILY OUT OF STOCK NO BACKORDERS

 

[JBswth]

Hey [emoji112], I'm new here and I have a new guy question that's probably been covered a million times

I wrecked my k10 and found a new frame, threw a cummins in it, blah blah, here's my issue as of late:

I mounted my cab/ core support and after I cut bigger holes on the mount pads, I am finding out that 73 to 80 frame yrs had different mount locations/hole sizes...

So I now have 81 style body mounts, and my 81 front clip now sticks out further than my 81 fenders

QUESTION: do I need to find a core support and fenders/hood from a 73 to 80 to fit to my older frame??? And will the body lines line up with my 81 cab and bed??

(Couple pics for attention)

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I did the opposite, when the front of my 81 1/2 ton, was damaged badly, I put an older style, (1978), front clip on it. I don't remember having any alignment problems. Everything fit fine.