HOW TO: front clip swap, 73-80 front clip on 80-87 cab/frame, square eye to round eye

There are no photo-documented tutorials for how to do this swap. None online that I could find. Therefore, I hope this information can be added to the collective knowledge of the squarebody community.

Below is a detailed pictorial of how I made this swap. I'm not saying it's the right way or the only way. I've never done anything like this before in my life, and I made some mistakes on the way. So please take everything I say with a big grain of salt. It took me nearly 4 full days of work!

Here's my new (to me) front clip, disassembling everything so I can take care of rust and paint the inside. It's from a '73 or '74 c20 I think.



First I started with the bumper. I unbolted the bumper and brackets from the frame first, but that was stupid. It would have been easier to remove the bumper from the brackets first, then the brackets from the frame. Another thing: you probably don't have to remove the bumper first. It would a LOT EASIER to get to the bolts with the core support out of the way.



Then the hood was next. That's my bud in the pics helping me with the heavy lifting.



I disconnected the battery, the wiring harness from the lights and horn and ground points, unbolted the radiator from the core support, and unbolted the fenders and inner fenders from the cab.

Last, I unbolted the core support from the frame through the body mounts. We had to remove the grill to get to the head of the bolt.



And then we just pulled it right off!





Here's me, looking confused:



I took the opportunity to clean and paint the firewall and inside the door jams.



Ok, so there's a discussion on a forum about this swap and, about fitting the 73-80 clip on the 81-87 frame, some swear up and down the street that you have to move the body mount perches on the frame and some swear up and down this same street that you do not. If it's true, then that means I have to somehow get off the huge rivets holding the body mount perch to the frame. Then weld it in place. Worse yet, if it has to move towards the cab, it will basically be impossible because the leaf spring shackles would be in the way.

The correct body/radiator-support bushing need to be used for the frame, not the radiator support. I.E. use the 81-87 bushings on the 81-97 frame. The 73-80 bushings are not wide enought and would fall through the hole in the perch. I just reused the bushing because I'm cheap.



Now I needed to figure out if this would be a problem or not. I first put the radiator core support on the frame and bolted the body mounts up. Then I put up the fenders on and just looked to see if the holes lined up. Good news! It fit just fine!





Even the body lines where easy, just needed a few shims. The hood doesn't quite fit right, not sure what to do about that yet. The hood did not come with the clip, the one that did was bent.





Speaking of bent hoods, I thought I'd loosen up the hood hinges by spraying the joints with lithium grease and working it in with a cheater extension on the hinge for leverage.



I don't know if that was a good idea or not, because it bent the stupid hinge! At first it wouldn't budge at all, so I gave it some more force. Still wouldn't budge! I started hanging on it like king kong, and that's when it started to buckle. Shat!

Sunday was spent retrofitting stuff, and driving to Kansas City to buy new hood hinges from LMC and picking up some used wiper posts and linkage. That wasted like 3 hours so I didn't get a whole lot finished, I was hoping to have it all finished by now but oh well.

I payed $80 for two hinges and I'm really not happy about it. After I bought them I went and picked up the wiper posts. The guy left them next to his garage for me to grab and when I did so, right next to it was a pair of used hood hinges! I couldn't get ahold of him but later he told me they could be mine for $20. A little rusty but, could have saved me $60! It's the things like this that can wreck a budget build like this one.

I didn't buy the $5 spring puller tool so I used vice grips instead. I found the best way to get the springs on was to install the hinge on the fender, then stand on the wheel and use all my might to wrestle the spring into place.



It ended with me saying me new catch phrase, "I should have been wearing safety gear."



Then I installed the battery tray. The battery is in a different orientation than 81-87 models, and because of this the ground cable will not reach far enough so I'll have to extend it.



The '74 radiator support plate will not work with my '83 radiator. I think the radiator is too tall.



But my '83 radaitor support brackets will not fit the '74 core support either!



So I had to fabricate my own brackets. I used the '83 radiator brackets and cut out a little bit of steel in the middle so I could bend down the bolt tabs.







The windshield wiper posts are not only different in height, but they also bolt to the cab differently. You also can't just swap out the posts onto the original linkage, you must use the linkage the new posts are on because they're riveted to it not bolted.



The driver side post could just use two of the three holes, but I had to hammer in the metal around it a little so that the wiper arm wouldn't it it. The passenger side post needed a hole to be drilled.



It's now Monday and my last chance to finish the swap before a week of rain begins. I have to work Mondays, but by the grace of God my boss sent me home today to work from home! Like that's going to happen...

First on the agenda today was to wire up the lights.



My advice for wiring up the headlights (I'm going from two headlights for low and high beam, to a single headlight for both) is to use the socket from the older style wiring harness but to NOT connect the same color wires - I had 2 green, 2 brown and 2 black coming from both the 74 headlamp socket and my '83 wiring harness. They don't match the orientation on the socket. Instead, match the wires to the orientation on the headlamp socket. What I mean is, on the 83 wiring harness's headlamp socket, the black wire was on the left but on the 74 headlamp, a green wire was on the left. So connect the green wire to the black wire. This worked for me, but I have no idea if it was dumb luck or not.

I was also able to pick up sockets for the turn signals for oreillies, and a "battery connector" cable that was the perfect length to lengthen the negative battery cable.

Next, I installed the hood. Got it on right before it started raining.



After I got it lined up as best as I could, I installed a brace kit. I had to be very careful to not put too much pressure on the drill, so that when I drilled throw the metal, it didn't continue and hit the sheet metal behind it and make a ding in the top of the hood.



Beginning to rain now, I was so happy to just close the hood with a good slam on the first try!



Can you tell that I used aftermarket hood hinges?





Stay tuned for more updates....

I still have to:

• install the grill (should be easy)
• install the front bumper (may require drilling in the frame for bolt hole locations)
• align the hood better

Nice work, I have been contemplating doing a full 73-74 conversion on my 82.

-- DISSASEMBLY --
* all parts are 81-87

1. remove the hood
2. remove the bumper and brackets
3. remove the battery
4. disconnect the wiring harness from the headlights, horn, ground point, etc.
5. unbolt the radiator from the core support (don't miss the two bolts on the bottom)
6. unbolt the fenders and inner fenders from the cab
7. unbolt the core support from the frame (the body mounts) (will have to remove grill to access them)
8. remove the front clip
9. remove the wiper arms and the cowl cover
10. remove the wiper linkage
11. remove the tall splined nubs from the wiper linkage
12. (optional) patch up the holes in the cowel where the hinges used to be
13. (optional) clean up and/or paint the fire wall

-- REASSEMBLY --
* all parts are 73-80, fully dissasembled

1. replace the wiper linkage
   • easier to do now before the fenders are on and in the way
   • can't just replace the splined nubs because they're rivited on
   • may have to hog out 2 out of 3 holes
   • I think all the wiper stuff was changed in '85, so you're millage may vary
2. install the plastic cowl piece and wiper arms
3. bolt just the radiator core support to the frame, using the bigger 81-87 rubber body mounts, the ones that came with the frame
4. bolt the inner fenders to the fenders
5. bolt one of the fenders to the cab and core support, keep the bolts snug but not torqued
6. if it doesn't fit then...
   • remove the body mount perchs from the frame
   • relocate it to the correct spot on the body, and either weld it or bolt it there
7. attach the other fender to the cab and core support, bolts snug but not torqued
8. align the body panels with shims
9. lay the hood down to see if there are any gaps that need work
10. torque down all the bolts
11. connect the radiator to the radiator core support
    • may need to fabricate brackets or find a radiator that fits
12. hook up the headlights, turn signals, and running lights
    • headlights
      • use the light sockets from the 73-80 wiring harness, cut them off and splice them into the existing wiring harness
      • pay attention not just to the color of wire, but to the orientation on the sockets, i.e. if ground (black) is left top or right on 81-87 light socket then it should be in same position on new light socket
    • turn singals
      • I bought new light sockets from Oreillies for $5 each, I connected the black wires together, the brown wires together, and what was left was one blue and one yellow wire and I connected those together. Seems to work just fine.
    • if you have a single headlight already, you may not need to do any cutting or splicing of wires for the headlights, just turn signals
    • the running lights use the same light socket so you don't have to cut those off, just reuse the same ones
13. install the battery tray and put the battery in
    • may need to extend the negative battery cable
14. install the grill, bezels, trim,
15. install the front bumper
    • won't be able to use the lower middle two bolts because the frame is cut off at that spot on 81-87 frames
    • you may need to drill a few holes in the frame

J Knight said:

Nice work, I have been contemplating doing a full 73-74 conversion on my 82.

Click to expand...

Do it!

Damn... that looks great. Maybe I'll do that some day.

What are you doing with the grille from the front end that you removed?

DLC said:

What are you doing with the grille from the front end that you removed?

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I sold the whole thing for $350.

Thanks for this, bought a "78" but chassis, fenders, hood are from an 82. Knew the grill and lights were wrong but didn't know the extent of what had been modified. Tracked the bin on the dash, was 82 and didn't match the 78 title. Good to know I don't have to swap the chassis too. I may be inundating you with questions this summer. Lol. This was extremely helpful. Thanks

It's been awhile but I'm pretty sure the way I removed my hood hinge springs, was open the hood so the spring was at max extension wedge penny's or Nicolas in between the coils then lowered the hood a bit reached in and pulled them out. I think my son was holding the hood while I did this. But prop rods would work.

Corey Roska said:

Thanks for this, bought a "78" but chassis, fenders, hood are from an 82. Knew the grill and lights were wrong but didn't know the extent of what had been modified. Tracked the bin on the dash, was 82 and didn't match the 78 title. Good to know I don't have to swap the chassis too. I may be inundating you with questions this summer. Lol. This was extremely helpful. Thanks

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I would suggest you get the title for the VIN that’s on your truck before you go putting a whole bunch of time and money into it.

@MannyDantyla,

Good work! Now you've got a '74 C10! Congratulations! lol

I was concerned that there would be a fit up problem at the top corner where the top of the fender met the top corner of the cab. I thought there would be some change there when GM changed the front clip to the down sloping fenders and hood like they did. I thought they also changed the top of the cab as well. But I guess they didn't, good.

I also was concerned about the valance and how GM changed it from the top of the hood in the '73-'80 model C10's, and put it on the top the firewall of the cab in '81. I didn't think the hood would fit there either. I thought the hood wouldn't close down enough at the top because all the valance and how the wipers were relocated back to the cab, and all.

Sorry for digging this up but i have a couple questions..

My '84 has the single square headlights currently. Would the existing wiring harness from that front end work with this front? I suppose i could go to the '79/80 front end and just reuse my current square LEDs if not.

What hood hinges were used? Im assuming the roundeye hinges and if so do they just bolt up in place of the 81-87 ones?