Yet another GMC build

[OKGMC4]

Old frame out. New one shoved in. Everything I could find said that a 58-59 frame is the same but front frame rails need to be shortened and bumper bracket holes redrilled. I found my core support holes don’t line up by 3/4 to 1 inch. Since they are riveted, removing the frame brackets and relocating them will be super fun. That was sarcasm. I was hoping to have that booger bolted tight today. On a side note, I think you can actually see how warped my front frame rails were in the photo.

[6DoF]

Originally Posted by OKGMC4

I found my core support holes don’t line up by 3/4 to 1 inch

in width or distance from the body mount?

if distance from the body mount, you can probably find that much just by loosening everything and biasing the cab to the chassis, the fenders to the core support, core to frame, etc.

if width, can you just add a plate to the core support?

[OKGMC4]

Originally Posted by 6DoF

in width or distance from the body mount?

if distance from the body mount, you can probably find that much just by loosening everything and biasing the cab to the chassis, the fenders to the core support, core to frame, etc.

if width, can you just add a plate to the core support?

The core support is behind the bracket holes. They line up perfect side to side but they are far enough back that the splash pan actually hits the bracket before fully in place. I thought about loosening the front but everything lines up so nice as it is. The core support holes are large and may allow me to tilt it but the splash pan is still a problem. Thinking to remove the brackets and lift the frame up and see where I’m at. May be able to relocate them or build my own.

[OKGMC4]

Could also try to tilt the core and trim the back of the splash pan to fit. Will investigate more

[Russell Ashley]

What's that front crossmember in the old frame out of? That thing looks huge.

[OKGMC4]

Originally Posted by Russell Ashley

What's that front crossmember in the old frame out of? That thing looks huge.

That is a corvette factory crossmember. It’s made out of stamped sheet metal and can flex under load. C4 suspension in a 55-59 usually puts the engine much farther forward and higher than the stock corvette. I had trouble keeping the alignment correct because all the weight was shifting things around. Shouldn’t be a problem with the new Flatout engineering crossmember.

[dsraven]

look in here for frame dimension drawings. the 58-59 frames are longer out front and the rad support brackets are in a different location. it's all ahead of the spring mounts so from there back they are the same.

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

[dsraven]

frame dimension drawings start in section 2 sheet 24. you are looking for sheet 33. a lot of the dimensions are given off the imaginary face of the cab line (firewall) so you may have to look closely to find the place where the rad support brackets are measured from. kinda looks like the center line of a cross member at the rear of the cab and takes a couple of dimensions to add up for the total dimension.
anyway, you'll figure it out.

[OKGMC4]

I ended up knocking out the rivets and moving the brackets back about 1”. Since it was kind of hard to access to drill new holes I just welded the brackets to the frame. Cab is bolted solid to the frame now. Got in the gas tank, battery drop box, and cleaned and painted the Dana 44 so should be able to start reinstalling suspension.

[joedoh]

good solution!

[OKGMC4]

So far so good. Still figuring out the firewall. Will either be homemade or a wheelbarrow. Deepest “big block” firewall is 4” recessed and I need 6”. Will have to move the gas pedal over, and the brake pedal. Vintage air unit may not fit right anymore. Plenty of obstacles that I’m sure have grand solutions. Just need to stare at it long enough and drink more coffee.

[daveshilling]

Originally Posted by OKGMC4

So far so good. Still figuring out the firewall. Will either be homemade or a wheelbarrow. Deepest “big block” firewall is 4” recessed and I need 6”. Will have to move the gas pedal over, and the brake pedal. Vintage air unit may not fit right anymore. Plenty of obstacles that I’m sure have grand solutions. Just need to stare at it long enough and drink more coffee.

I'm doing an LS on a c4 Front, and that's a healthy setback!! I actually ended up cutting up my mounts to try again since I wasn't doing the firewall. Are you trying to make clearance for turbo piping and an intercooler?

[OKGMC4]

Originally Posted by daveshilling

I'm doing an LS on a c4 Front, and that's a healthy setback!! I actually ended up cutting up my mounts to try again since I wasn't doing the firewall. Are you trying to make clearance for turbo piping and an intercooler?

Yep. That's about where an LT1 was placed in the original C4 and it should restore the balance for better handling. I should be able to put the intercooler where the radiator was, and make a new mount for the radiator just after that. If you don't want to cut the firewall you have to get the engine over the rack with the rack between the balancer and oil pan.

[solidaxel]

That looks like a lot of engine set back

[6DoF]

holy mid-engine batman!

the Cummins needed a 6" doghouse too, but wasn't that wide. while a wheelbarrow would be sweet, i'd be more worried about keeping the doghouse as narrow as possible.

[dsraven]

I recommend to sit in the cab area and place your feet where the pedals would be. Nothing worse than a cramped accel pedal on a long ride and you need room for your foot to access the brake pedal easily. Try to make the firewall recess as narrow as possible. Maybe even a removable cover like a van has. Also think of shape if you plan on upholstering it. If a wheelbarrow is the shape you like but too wide, you could split it and seam down the middle. If going with sheet metal from scratch, mock it up with posterboard or even wood veneer and tape.

[OKGMC4]

Im seeing what you guys are saying. The width is more of an issue on this narrow cab than it would be on a c10. To get this to work I’ll have to relocate the gas pedal and therefore the brake pedal. It interferes with the brake booster bracket and might as well scoot the column and gauges. I have 4” of room to move the seat over, too. And new carpet. Plus my vintage air won’t fit but it looks like an Old Air Hurricane will. Im just being stubborn about making it work. Truck was a great driver but could never turn corners despite the c4 suspension.

[OKGMC4]

Inspiration.

[Rickysnickers]

What truck is at the bottom, with the interior shot?

[OKGMC4]

Originally Posted by Rickysnickers

What truck is at the bottom, with the interior shot?

The single turbo engine and the interior go with this truck. A little more utilitarian than I d prefer but still pretty awesome.

[Rickysnickers]

Originally Posted by OKGMC4

The single turbo engine and the interior go with this truck. A little more utilitarian than I d prefer but still pretty awesome.

Yeah, it is. I like the roll cage in it though. It appears to be tucked out of the way nicely and he probably has four point belts attached to it. Thanks for the photo.

[OKGMC4]

Wheelbarrow seems to work. I like that it’s curved. Anything I could’ve made would be all sharp angles. Going to recycle the hump from the firewall as the transmission bump. Then on to relocation of pretty much everything else in the cab.

[layinrocker65]

Looks nice. Love the set back

[OKGMC4]

The gas pedal is pretty much where the brake used to be. I had to move the booster bracket over a couple inches. By grinding the welds on the brake pedal arm, I can now move it to the other side of the swing arm shaft. I put a seat back in and the gas pedal feels comfortable where it’s at but I think the brake pedal is going to be a left foot operation. Driving with both feet doesn’t really bother me any more than using a clutch. I’m just going to leave the column and seat locations alone.

[dsraven]

That would drive me crazy, but, to each their own.
Is there room for your left foot anywhere when not being used for the brakes?
Have you checked local laws for foot and pedal clearance laws, if any exist? Wouldn't wanna find out AFTER doing all that work.