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'76 C20 - First Truck

Mr_Vaughan

Member
Joined
Apr 26, 2023
I've decided this is a good place to post about all my truck related work. I've had it for a while, and there's a story somewhere on this page about how I got it, but i'll give y'all another run down.
In 2023 as the conclusion to my road trip to New York, I brought this truck home from New York. it was my grandpa's, and it had been parked for around a decade. it got a new fuel system and a few little things to get it back, and has been an ongoing project since. it's a '76 C20 with a 292 I6, SM465, and 4.56 gov lock 14 bolt. slow and gutless, but a nice truck. it has an 8' service bed that's more rust than steel, and the body only gets worse the further forward you go. it has a mismatched fender and doors that I put on it, and a monstrous brush guard I built.

this was on the way home from New York, with the hood off due to overheating and the original fender still on.
Squarebody hood off by Levi Vaughan, on Flickr

My senior picture with the truck
1000001371 by Levi Vaughan, on Flickr

our whole "gang" at school - My brother's blazer, my friends f250, and another friends thunderbird. all from the 70s.
1000001436 by Levi Vaughan, on Flickr

it's been through many an upgrade since i've had it, but i can't hardly remember most of them.
I put a new radio in it, because the old one was questionable and i wanted bluetooth. a couple hundred bucks got me a retrosound head unit, and my brother had some old skar 6.5" speakers in a homemade box that he donated to the cause. it sounded good, but unfortunately the fact that i have the speakers behind the seats obscures a lot of the upper frequencies especially when the engine is loud (3k at 65) and so i added some little ones in front of the seat that allow better clarity, with the rear ones hitting hard. it's a well balanced system and i couldn't ask for any better in such an old truck.

the bumper itself was a fun task, i built it in my welding class. it was on one of my dad's trucks in new york, but i cut it apart and rebuilt it to fit the truck. it's something like 6 inch angle iron 3/8" thick, with 1,4" thick 1 1/4 angle iron framing and expanded steel over the whole thing. it weighs about 300 lbs, and could probably hit a cow and come away unscathed.

recently, i put a different engine in it. it has been worn out since ive had it, and it got to the point i couldn't justify driving it as it burned almost as much oil as it did fuel, and it burns a LOT of fuel. i stayed with a 292, just one in better shape. along with the engine came a new clutch, as the old one had been slipping slightly and i figured it was an opportune time to change it.

with the new engine, several issues became clear: the exhaust was LOUD, as it would no longer keep a seal on the meanifold.

the rust was starting to bug me more and more

the power steering still leaked badly.

the alternator, a source of consternation, was acting more erratically than ever, charging from 10 to 18 volts with no rhyme or reason.

ill cover the fixes to those in another post, gotta go be a student.
 
i know you all love pics, but i rarely take the time to get many, so bear with me.
this is the only real picture i have from the engine swap.
1000001412 by Levi Vaughan, on Flickr

the first of the afformentioned problems i addressed was some of the rust. certainly not all of it, not even much of it but some. the right rear toolbox had no floor, and i wanted to use it. so i cut out the rust, patched in some metal, and painted it up. it was my first foray into body work, and it was with OA welding, and i followed pretty much no recommended procedure, but i got it done. i honestly enjoyed it.

before
1000001755 by Levi Vaughan, on Flickr

after
1000001755 by Levi Vaughan, on Flickr

i keep spare parts in that box now, and its not life changing to have but it just makes me feel good to know that i built a floor for it.

the next issue i fixed was the exhaust. the flange where the pipe meets the manifold was completely mangled, so i cut about a foot of pipe off, and replaced it with flex tubing (part of the issue was misalignment, which i didn't want to fix properly) and a custom made flange. i wish i had taken pictures of the flange, as it is something i'm proud of, but unfortunately i didn't. it was a step up adapter that i pounded a steel cone into to give it a flare at the end so that the "donut" would be captured. it worked perfectly. the truck went from ear shattering at idle to managaeable at 60.

last night, i think i got the power steering fixed. the pump turned out to have a hole next to the pressure fitting, which fluid was flowing out of. it's barely visible in this picture:
1000001755 by Levi Vaughan, on Flickr

a little bit of brazing, and it sealed up nicely.
20250403_202542 by Levi Vaughan, on Flickr

after that, i dealt with the alternator wiring. the factory routing has it going over the top of the engine on the drivers side, which happens to be where the exhaust manifold connects. in other words, it gets hot. by the time i got ahold of the truck, the 3 wires had collectively been re insulated or spliced over 10 times. i ripped the original wiring out, tracing all 3 to their origins. i replaced all 3, and sized up the main charge wire so that i can safely upgrade the laternator in the future if i so wish. i also re routed the wiring to go across the inner fender, keep it out of the major engine hot spots. i used a 1/4-20 rivnut to hold an adel clamp to keep the wiring in place.

original wiring:
20250403_212500 by Levi Vaughan, on Flickr

new wiring:
20250404_000645 by Levi Vaughan, on Flickr

a few other miscellaneous things i've done that are worth noting:

trailer wiring - the original taillight wiring was one of the biggest issues i faced, and there were no provisions for trailer lights or brakes. i solved that by installing a junction box at the rear of the frame, and running new wire for trailer brakes. i installed a 7 pin round connector on the bumper, and a brake controller in place of the ashtray.

all i have pictures of is the junction box, a philips clear vu. i highly recommend it, allows for wonderful wire management and expandability.
20240615_084704 by Levi Vaughan, on Flickr

that's all for now, planning to take it to a cars and coffee event tomorrow so we'll see how it does on the highway then.
 
so... Saturday was kind of a disaster.

we set out late, after my brother spent a bunch of time cleaning his truck out and changing the oil. I took the lead, as I didn't want him to outpace me and leave me behind in his much faster rig. we got about 3/4of the way there, and my truck started overcharging again - not intermittently, constantly. it seems that the voltage regulator in my alternator finally died. not a huge deal, as I have a rebuild kit sitting in the bed, but the power steering seems to still be leaking and dumping fluid all over the alt. I cannot for the life of me figure out why GM put the steering pump OVER the alternator on these things, as any kind of a leak just drenches the alternator in hydraulic fluid. very dump. anyhow, I want to get the steering fixed properly before rebuilding the alternator, so as to not immediately cook the new parts.

so, any recommendations on decent affordable Saginaw power steering pumps? i'm on my second one from my stockpile of parts here, and the last one I have is set up for hydro boost, meaning it has an extra return line i'd have to plug off. I can use it if I must, but it would need the pressure fitting swapped out as well and i'm not sure that that's not the root of my problems. so if I can find a cheap optio for a rebuilt one, I might just get it to save the hassle.
 
The GM power steering pumps were made by the millions, so if you look in your local pull-a-part or search on ebay, car-part.com, etc. you'll probably find a good used pump to keep you going.
 
The GM power steering pumps were made by the millions, so if you look in your local pull-a-part or search on ebay, car-part.com, etc. you'll probably find a good used pump to keep you going.
yeah. definitely the nice thing about GM.
 
recently i found this truck in a junkyard: a 2002 chevy 2500HD with an 8.1 BBC and a ZF6.

20260714_074057 by Levi Vaughan, on Flickr
20260714_074101 by Levi Vaughan, on Flickr
20260714_074105 by Levi Vaughan, on Flickr
20260714_074109 by Levi Vaughan, on Flickr

It's a super rare drivetrain, and an awesome combo for truck work - the engine is obviously a power house, and the transmission is just awesome. the gear splits are much better than the NV4500, and it's stronger to boot. unfortunately, the case is cracked, so i'm not sure what its fate will be. for now, though, the engine is getting packed into my squarebody.

the owner of the scrapyard is a buddy of my boss, so he was nice enough to haul it to our shop and let me pull it apart there. i took the pictures of both trucks because they're similarly optioned - big block, manual, floor shift 4x4, 4.10 gears. the white one is my current workhorse, 99 k3500 with a 454/NV4500. i love it.

20260725_113818 by Levi Vaughan, on Flickr
20260725_124214 by Levi Vaughan, on Flickr

after all was said and done, hauling the hulk back to the scrap yard.

20260730_081957 by Levi Vaughan, on Flickr

this was one of 2 loads, all the major stuff. lots of really cool, rare parts on this thing.

20260730_135251 by Levi Vaughan, on Flickr
20260730_172150 by Levi Vaughan, on Flickr

getting the 8.1 to fit the squarebody is not hard. it uses the same mounts and headers as a 454, which came factory in these trucks. the only thing i need to change to make it fit is the passenger side frame stand, because the 292 I6 is the only engine in a squartebody that used a different mount, and it's what i have. i have motor mount clamshells, headers, and dual pipes all the way to the back from a 454 truck i parted out a while back. the transmission will bolt up, i just need to use the clutch from the 292 because the pressure plate is a different height. wiring is the only hard part, and only because i'm trying to graft the entire 02 harness into the squarebody. i'm tired of unsealed electrical connectors, so this is a good time to fix that. it'll also get me away from glass fuses, and have relays for things. i don't miond electrical work, so this isn't a problem for me, even if it is tedious.

20260730_194915 by Levi Vaughan, on Flickr
20260801_000053 by Levi Vaughan, on Flickr

this is the cracked zf6 case. new case halves are not available, and used ones are not cheap. ill either sell the whole thing, or tuck it away and fix it later. not sure yet. there is a lot more damage than this, most of the whole front face is gone/broken and several spots further back are cracked. the tailhousing has a crack as well, but i think it might be repairable. if nothing else new tailhousings are available, but also not cheap. the two housings would cost more than i have into the whole drivetrain.

20260729_080945 by Levi Vaughan, on Flickr
 
Seems to me you could actually tig that case back together if the damage is confined to what is observable in the photo. Might actually be worth the effort on that trans. Nice project!
 
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