55.2-59 1/2 ton SWB GMC vs Chevy frames

[blap]

Is there any difference between a gmc frame and a chevrolet frame?

[G&R's57GMC]

Yes they are different.
The rad support on the Chevy mounts at 2 points on the frame rails.
While the GMC mounts to the center of the front crossmember which is also different then the Chevy.

I’m using a Chevy frame under my GMC and using the Chevy rad support . This will require me to fab supports for the hood latch panel so I can use the GMC hood and grill .

Or I can use the Chevy hood latch panel and latch along with the Chevy hood striker support swapped from a Chevy hood and replacing the GMC hood striker support. Doing that I’ll also have to figure out a way to support the GMC center whisker of the grill surround .

Or do the above and use a Chevy hood .

Or ditch the GMC hood and grill and make it a ‘57 Chevy .

[blap]

G&R's57GMC Are the frames the same length ,width. The rad support the major difference?

[dsraven]

some of the GMC's use the Chevy rad support and some don't. a GMC rad support is made differently (for USA trucks anyway. Canadian GMC's use a Chevy rad support) so the cross member is also different I think. maybe the assembly manual drawings will point that out, not sure. 58-59 frames is also different than the earlier 3 years because the front clip is longer. those have the rad support mounts further forward on the frame as well to match up. 58-59 also is longer ahead of the rad support because there is a longer filler panel between the bumper and the sheet metal. the frames are the same width. I believe the frames are the same behind the front spring hangers. the cabs are the same except for the dash. the doors interchange etc. the front fenders are different for 57 because they have a different grille surround parts. GMC fenders have a divet around the area of the mustache grille part where it wraps around the fender for the signal marker light. emblem placement on the fenders differ between years if that matters to you. other than the tailgate emblem I think the box is the same.

assembly manual

https://www.trifive.com/d1/55-59Assy.pdf

here is a chevy rad support for 55-57. if you look a little deeper you can find a 58-59 rad support.

https://www.brotherstrucks.com/1955-...tinfo/RSB5000/


here is a thread that explains a few things better because it has pics. scroll down and you will see the GMC rad support.

http://67-72chevytrucks.com/vboard/s...d.php?t=754736

[dsraven]

I used a 58chevy frame under a 57 GMC. I moved the rad support frame brackets to match and cut the frame off ahead of the rad support to match a 55-57 frame length there for the bumper mounts. the assembly manual will have those dimensions, you just have to look hard ay how they figure things out referencing other dimension reference places.

[dsraven]

shouldda mentioned, my 57 gmc is a Canadian truck so the Chevy rad support was used from the factory. I also think some of the cheaper versions of these trucks used parts from whatever they had laying around. I have seen pics of a 4 eyed truck with adapters in the headlight areas to use single beams on each side. different grilles etc.

[mr48chev]

Originally Posted by dsraven

shouldda mentioned, my 57 gmc is a Canadian truck so the Chevy rad support was used from the factory. I also think some of the cheaper versions of these trucks used parts from whatever they had laying around. I have seen pics of a 4 eyed truck with adapters in the headlight areas to use single beams on each side. different grilles etc.

I'm thinking that those 58/59 trucks with the single headlights and odd grill were built for fleet use.

[dsraven]

Mr48, that's the term I was trying to think of. Fleet option. Kind of a mix and match between different years of trucks. Like whatever they had extra of or was possibly cheaper to build. I think headlights and grilles were the easiest noticed differences.

[dsraven]

Here is some I fo from the HAMB forum talking about the fleet option. Kinda interesting.

https://www.jalopyjournal.com/forum/...-truck.336844/

[dsraven]

here is a look at the Canadian GMC grille surround upper mounting and the cross bar that supports the hood latch etc. the cross bar simply bolts to short lengths of "angle iron" which are also bolted to the fenders on each side. easily home made and if anyone needs dimensions on those let me know. these are pics from my 57. it uses the Chevy rad support but looks like any other 57 gmc with the hood cut away and the jynormous grille and bumper parts. one should be able to source the hood latch and all the rest of the parts required to make a GMC hood and latch fit with the Chevy rad support.
disregard engine stuck in there.

[whitedog76]

I believe, I just saw a Vortec 4200/ Enlighten us DSRAVEN.

[dsraven]

yep. 4,2l vortec. good eye.
I started my 57 GMC build with 2 trucks. a 57 GMC long box 3/4 ton stepside farm truck that had possibly rear ended a grain truck at some point, front fenders/hood hit the deck of the grain truck just above the headlights level on the 57, I assume grain truck because the GMC only really spent a couple of years on the road before it became the farm truck full time. I ended up cutting that cab apart because it was tweaked and the doors wouldn't fit properly after I rehinged them. the openings weren't right to fit the doors. the other donor was a 58 Chev 1/2 ton long box fleetside. both were 235, 3 on the tree trucks. the chevy had a hard life and the fleetside was caved in on one side and quite badly rusted everywhere. the GMC ran, it actually started in -30 with just a boost. not plugged in. I drove it up onto a Uhaul deck trailer under it's own power. no brakes to speak of but it ran. the 58 was also a farm truck but it wasn't running, however was not siezed, I just didn't spend any time trying. I sold the drivelines from both because I planned a 4.8l LS engine with auto trans. I used the frame from the 58 because the 57 had been a hydraulic deck truck and the frame was butchered. the 58 frame got cleaned, blasted, boxed, etc and a TCI MII front end was welded in. complete with airbags, p/s etc. it was an ordeal because the cross member turned out to be for a different truck than mine so it didn't fit the frame well, lots of air gaps between the parts. like 1/2" airgaps . I tried to get some dimensional and geometry info from TCI but it was real vague. the supplier I bought it from was just that, a supplier. no help there either. since I am a journeyman mechanic before becoming a Firefighter I figured out the geometry and made it work properly but wasn't impressed. one day I was doing some work on my nephews chevy trailblazer and thought the under side would fit under my old truck. that would give me bigger brakes, rear air ride if I wanted it or stick with the coils, 4 link rear, posi with decent gear ratio (3.73), decent park brake set up with a floor mounted stock brake lever, a steering column with tilt and wiper switches etc, a decent set of pedals with drive by wire accel pedal built in, rack and pinion steering, strut front suspension with lowering kits available. auto with O/D, fuel injection with a fuel tank etc already in place, complete exhaust system (for now but will upgrade later), a complete driveline so no goofing around getting driveshafts built, all wheel drive and an inline 6 that has comparable torque and hp to the 4.8 that I was going to use in the first place. besides, it has some "what the heck" factor as well because you don't see too many customs with an inline 6. long story short I was looking at doing that when another member on here started a project doing that same thing. except with a v8. we did some chatting back and forth and I found a 2004 GMC envoy at an insurance lot for cheap and the project took a turn down a rabbit trail.
SO, you are right. 4.2l Atlas vortec under my hood. if it turns out to have not enough juice to pull my boat out of the water then I will turbo it or something, lol. worst case scenario the envoy did come with a v8 option that could easily be adapted into my truck.
my 57 uses the complete envoy undercarriage and engine/driveline. the frame is modified ahead of the engine to accept the stock bumper. I used the floor and firewall from the envoy and grafted that into my 57 cab since it was quite rusty on the lower 1/2 including the floor which needed to be replaced anyway. the envoy was an XUV, which was a different unit that was longer wheelbase and had a sliding rear roof and a midgate. kinda a cool idea but not something everybody wants. I used the frame as is without shortening it because I wanted to extend the cab to fit high back buckets with integrated seatbelts. the wheelbase was just right. another envoy bonus especially if I use the envoy floor, console, carpet etc. off the shelf purchases when the time comes to do the carpet if I don't like the look of the original carpet. this will be a daily driver so not looking for perfection. I will use the envoy heater as well because it fits right into the firewall and will be an easy fix to get the A/C working etc. again, off the shelf parts usually in stock at a local auto parts place.
so, now you know.
here are some pics of the before trucks and sorta what it looks like with the envoy under it. newer style box with old fenders bolted on.

[dsraven]

Here is a better pic. Sort of.

[blap]

Nice Truck!!!

[G&R's57GMC]

dsraven that bracket between the rad support and latch support doesn't seem to add much as the latch support is solid . Was that a stock unmodified piece or something you modded . Do you feel it's necessary .

I'm going to run a '59 Chevy Chassis with the Chevy rad support
with my '57 GMC .

[dsraven]

thanks blap, appreciated. don't mean to hijack the thread, I got carried away with my quick answer to whitedog's inquiry.

what's your plan? whaddya got to work with? got any pics? do you have an idea of what you want when it's done? whats your experience, tool assortment available, space to work in etc?

[dsraven]

G&R, that is a stock GMC part used on the Canadian GMC truck. I think it could be left out but it does support the latch bracket so it is sturdier I think. it looks like it may have been modified but I think the original owner just straightened it after the truck had a little accident. the hood latch and that bracket were likely bent a bit from the look of the damage that the hood absorbed. I think the farmer who owned the truck was pretty innovative with repairs that only cost labor.

[G&R's57GMC]

Thanks dsraven

Hope this also helps the OP

[dsraven]

found it finally. a pic of the 58 frame uinder the 57 GMC which uses the 57 chev rad support. it shows where the longer chevy frame (58-9 version) will be cut off and drilled for the bumper mounts. also shows how much the rad support mounts needed to move forward if you look closely there you can see the 58-9 rad support holes ahead of the 57 gmc mounts.