Help with late body on early frame

[SquareBox86]

Before I dig too deep in my latest project I though I'd ask around for some help/advice.
I have a 85 and a 86 k10 short bed trucks that I'm making one out of. Both frames were junk, i found what was said to be a late frame that was in perfect shape so I bought it. All the bracket rivets were shaved off already and the brackets were in a box. I had it blasted, gave it a quick coat and started bolting the brackets on...that's when I realized I had a problem. When I was putting on the radiator core support bracket I noticed that that it (there was only 1 in the box) was an early (pre 80) type. Measured the holes on the frame and a compared it to my 85 and 86...2 1/2" oc holes on the frame 2 3/4" oc holes on the 85 and 86 frames so right there I knew I had a early frame. I found the numbers on the frame in 2 spots and both matched: C8F343951 So if we try to decode this we get:
C8F343951
C=Chevy
8=???? Should be c or k
F= Is for engine
3=3/4 ton
4=pickup
3=1973
...so according to my research I have a 73 c or k 3/4t pick up frame...correct me if im wrong
So obviously before I go further I wanted to make sure this is going to work. What I learned online so far is that it should...with these modifications:
1) you have to cut the nose of the frame to clear the bumper
2) order body mounts for the frame NOT the cab year
...that's all I found online so far but walking around the frame I noticed these:
1) the rad core supports are different, early ones aren't available so I took the late ones I had an dropped the top holes 1/4"...now they bolt to the frame and are at the same height as the early one was
2) there are no holes for the late front brake hose brackets and it looks like the brakes go thru the frame at a different spot
3) the early uses a different e brake system, late is way easier but no holes for that either
The no holes thing is an easy fix but that's just stuff I noticed...the big question is what else am I missing like:
1) what brake and fuel lines to use
2) what gas tanks and hangers
3) what mods to the frame before it gets final coat
4) etc etc etc
Any help with what I should be checking and/or parts I should be ordering would be appreciated

[aggie91]

The early frame should work with the changes you mention.

The tanks & brackets from your 85/86 should work and bolt on to the frame in the correct spots. you might have to drill a hole or two, but that is easy like you said.

Brake lines do go thru the frame in different spots for the front. That should be an easy fix with a uni-bit. I would use the brake lines from your 85/86. drill mounting holes as needed...

if it is a 3/4t frame, you need to check that the spring mounts both front and rear will work with your 1/2t parts...

I would mock everything up to a rolling chassis state before doing any final coating...

[chillman88]

Subscribed. I'll be doing the same thing with a 79 frame on my 86.

[SquareBox86]

Originally Posted by aggie91

The early frame should work with the changes you mention.

The tanks & brackets from your 85/86 should work and bolt on to the frame in the correct spots. you might have to drill a hole or two, but that is easy like you said.

Brake lines do go thru the frame in different spots for the front. That should be an easy fix with a uni-bit. I would use the brake lines from your 85/86. drill mounting holes as needed...

if it is a 3/4t frame, you need to check that the spring mounts both front and rear will work with your 1/2t parts...

I would mock everything up to a rolling chassis state before doing any final coating...

Cool thanks for the info...that's what I'm doing now, mocking it up. I have the rear axle set in its mounts already...no problem there. The front I'm in the middle of blasting now, should be bolting it on soon...what's usually the problem with the 3/4t vs 1/2t mounting?

[aggie91]

The 3/4t frame is taller (cross section of the rail) than a 1/2t frame. Sometimes I have seen the spring mounts not line up, but sounds like your rear mounts worked out fine, so the fronts should too.

[hatzie]

Originally Posted by SquareBox86

Before I dig too deep in my latest project I though I'd ask around for some help/advice.
I have a 85 and a 86 k10 short bed trucks that I'm making one out of. Both frames were junk, i found what was said to be a late frame that was in perfect shape so I bought it. All the bracket rivets were shaved off already and the brackets were in a box. I had it blasted, gave it a quick coat and started bolting the brackets on...that's when I realized I had a problem. When I was putting on the radiator core support bracket I noticed that that it (there was only 1 in the box) was an early (pre 80) type. Measured the holes on the frame and a compared it to my 85 and 86...2 1/2" oc holes on the frame 2 3/4" oc holes on the 85 and 86 frames so right there I knew I had a early frame. I found the numbers on the frame in 2 spots and both matched: C8F343951 So if we try to decode this we get:
C8F343951
C=Chevy
8=???? Should be c or k
F= Is for engine
3=3/4 ton
4=pickup
3=1973
...so according to my research I have a 73 c or k 3/4t pick up frame...correct me if im wrong

Are you sure it's not CKY343F51?
The 4th digit says it's a 30 series 1 ton not a 20 series 3/4 ton.

GM 1973-1978 Parts Book #51 VIN pages

[SquareBox86]

Pic of the numbers:

[SquareBox86]

Yeah you're right too it's 1 ton, 3 = 1 ton not 3/4 ton. But those are the frame numbers in the pic...what the hell do they mean?

[hatzie]

I'm no expert on partial VIN #s. The engine VIN #s always seem to be a little chopped up...

Some Flint Models six digit sequence # started at 300000

Could it be...
C=Chevrolet Division
8=1978
F=Flint
343951 is the assembly sequence number

[SquareBox86]

Beats me, I'm working on it right now, front axle looks like it's going to go in ok...after I finish moding the energy suspension sleeves, ugh

[SquareBox86]

Well the axles fit at least

[hatzie]

That looks like a 1/2 ton frame. Since the K10 springs fit with no drama I bet it is.

[aggie91]

I agree with Hatzie, that looks like a 1/2 ton frame. How tall is the frame rail in the straight section that would be under the cab?

[SquareBox86]

I don't have it in front of me but I think it was 6". I measured it yesterday and it was the same as the 85's 1/2t...same wall thickness too. So whatever the number on frame is it's completely crap

[hatzie]

My WAG on the partial VIN seems to match the numbers... That frame, it would seem, has the division and then the last 8 of the VIN.

We have the division and the last 8... Pretty easy to extrapolate the rest of the original VIN. You can probably assume it's a 4x4 frame because the front spring hanger holes are present. It's a 1/2 ton frame. The only unknown is the engine... Common V8 engines in 1/2 ton 4x4 are the 350 or 305... As a 1/2 ton 4x4 it couldn't have the Diesel, the 292 I6, or the HD 454. The 250 I6, 400 SB and the LD 454 would be fairly unusual in a 1/2 ton 4x4.
350 engine CKL148F343951 or 305 engine CKU148F343951 would be pretty solid guesses.

[gmachinz]

Only because I'm dealing with this now too- (a late 70's 4x4 frame with an 86 body) another issue is the frame brackets for the front bumper. The frame used a single hole to bolt to frame-1981 up mounts with 2 holes. Also, the 73-80 frame horn end bolted directly to the bumper-well in 1981-up the end of the frames are cut at about a 45-degree angle and there is a 90-degree bracket that bolts over the end of the frame, then that bolts to the front bumper. Nothing too complicated but careful measurements need to be made so that the front bumper filler panel and the bumper itself sits level where it needs to be....no way to mix/match the various parts because no matter what it will look odd. Gotta go with whatever body style you're running and modify the frame as needed.

[SquareBox86]

Nose

[SquareBox86]

Those are late radiator support brackets on there too

[gmachinz]

Here is a pic showing the 81-up style frame....notice the angle of the front on both horns-no idea whose truck this is-I just saved a google image of one for reference.

[chillman88]

I'm not intending to thread-jack, but what's the deal with 81-87 body on 73-80 frame as far as the radiator supports? I've read both that the older mounts need to be moved, and I've also heard they do not. What have you found in your research? I'm hoping to get my frame galvanized and want to have all the drilling/cutting done before I do so.

[SquareBox86]

I only had 1 73-80 mount, I bought a new 81-87 mount. When I went to bolt it on the frame the top to bottom holes were off by 1/4". You can't buy early mounts so I took one off the one of my late trucks. I compared the 2 and it worked out the all I had to do was lower the top holes on mounts 1/4" to fit the frame. The heights worked out the same too...are they in the right position I don't know. I couldn't find anything online...hence why I asked these questions in the beginning of the post. I'll take some measurements off the late frame and see tho

[SquareBox86]

Took some rough measurements from the front body mounts and they were the same. Set a core support on them and the bolt holes were on center. So it looks ok to me???

[chillman88]

Originally Posted by SquareBox86

Took some rough measurements from the front body mounts and they were the same. Set a core support on them and the bolt holes were on center. So it looks ok to me???

Oh thank you, I've heard both ways so hearing from you that they look like they're the same gives me one less issue to worry about!

[Titomars]

Originally Posted by SquareBox86

Yeah you're right too it's 1 ton, 3 = 1 ton not 3/4 ton. But those are the frame numbers in the pic...what the hell do they mean?

That is basically the last half of the original VIN. The last six is the sequence number. the stamping will include plant, year, division, and sequence if I remember correctly
GM did not stamp the entire VIN on the frames back then.
so it would be:
C= Chev
8= year
F= Flint
343951= final unit number

[hatzie]

Originally Posted by Titomars

That is basically the last half of the original VIN. The last six is the sequence number. the stamping will include plant, year, division, and sequence if I remember correctly
GM did not stamp the entire VIN on the frames back then.
so it would be:
C= Chev
8= year
F= Flint
343951= final unit number

Yup
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