’48 GMC Build – Cummins 4BT, 47RH, IFS, 4-Link, Air

[reg3]

Hey everyone, I’m finally ready to start a build thread on my 1948 GMC FC152 (3/4 Ton, Longbed). This is my first full build; I’ve been working on the truck slowly over the past few years, progress has been a bit slow but I’m finally rolling on it now and wanted to get a thread going. Ill catch up in the first few posts, then update it as I finish work on it. So without further ado….

Backstory: I came across the truck through a friend who pulled it out of a barn on a big farm in South Dakota from the original owner. The truck was a perfect example of a rust free-all original survivor that had some mechanical issues some years back and was pushed to the back of a barn and forgotten about. The truck had a great patina on it; all the body panels were original and (relatively) dent/damage free. Unfortunately at some point on the trip to the east coast, the transport guy smashed the truck into something while offloading it (he was shocked that the brake pedal went all the way to the floor when he tried to stop ). The damage was primarily to the front grille surround/fenders, nothing too catastrophic, just a bit of bad luck. Because of this incident, my friend soured on the truck and decided to part ways with it, and this is how it came to live in my barn.

Build Plans:

• Chassis: Modify original frame, C-Notch rear, IFS front
• Suspensions: Air on all 4 corners, Mustang II, triangulated 4-link rear, Ford 9-inch
• Drivetrain: Cummins 4BT, 47RH automatic, hoping to land somewhere in the 300HP range
• Power/Engine: ARP Head studs, 60# Valve Springs, 4K GSK, Fuel Plate Mod, DDP Stage 2 Injectors, Timing ~16.5*, Turbo: undecided here (either HY35W or super HX30)
• Exterior: CLR, scotch brite, clear coat
• Interior: new leathers on the seats, headliner, gauges. Keep the original interior paint and trim, CLR, scotch brite, clear coat

My goal for the build is to have a reliable, mild HP, patina queen with an updated drivetrain/brakes, that the wife and I can comfortably cruise in.

Now on to some pictures…

Crappy cell phone pics from the day I picked it up, notice the front end damage in the first pic.





I rolled it into my little barn and began the tear down...

[reg3]

After finishing up the teardown, I started to put together the front suspension. We decided to go with a FatMan Fab Stage IV Mustang II Hub-to Hub Air-bag Kit with a power rack. Pretty happy with the quality of the parts, build quality was pretty good on the kit.



Getting the cross-member centered and leveled.



I welded on a temporary piece of angle iron on to the upper bag mounts to keep them level and properly aligned.



Cross member and upper bag mount tacked in place.



Passenger side test fit.



Finish welded



Cut in the rack arm clearance inserts and sprayed some temp. primer on everything. Full test fit of the driver & passenger side as well as the rack. Everything fit really well and cycled smoothly.

[reg3]

I picked up the engine a few days after bringing the truck home, donor truck was a 1994 Grumman box truck. The engine is a Cummins 4BTAA, 130 HP aftercooled variant (CPL: 1839). It had a little over 100k miles when I picked it up, ran pretty strong, had minimal blowby and wasn’t blowing too much smoke.

Build Plans for the engine:

• Full rebuild, seals/bearings/gaskets, rotate oilpan (swap front pickup to rear pickup), KDP
• ARP Head Studs, 60# valve springs, 4K GSK, DDP Stage 2 Injectors, Modified fuel plate, timing 16.5*
• Modified 5.9/12V echaust header (cut and welded cylinders #1/#6) to make a center dump manifold

Turbo: this has been something I haven’t finalized yet. I initially thought about going with a HY35W off a 5.9/24V but I am moving now more towards a super HX30W (assy: 2835278).

Unfortunately during the teardown, I found that the head was cracked between the intake/exhaust valves on cylinder #3. So had to make a run up to my local Cummins parts distributor and pickup a new head (ouch). It wasn’t all bad news however, cylinder walls/pistons, main and rod bearings all looked almost brand new. I got it all buttoned back up and sprayed some fresh Cummins beige.

Pulled the engine using my 'specialized' orange cherry picker lol (Overkill is Underrated )

[reg3]

Got to work fitting the engine in the truck and building some engine mounts. It took a bit of time to get the engine sitting exactly where I wanted it but I am happy where it ended up. I reused the existing 45* engine mount brackets (with some slight modifications) and used Dodge D250/Cummins rubber engine mounts. I fab’d up some mounts on the frame to accept the D250 mounts, these landed nicely around the upper bag mount.

I mounted the engine as low as I could but wanted to keep the oil pan above the level of the front x-member to avoid dragging the oil pan when the truck is aired out. Because these engines are relatively tall, I needed to get the old cutting wheel out and make some room in the cab for the transmission.

[reg3]

The OEM floors were in decent shape, but after cutting them up to fit the motor, I decided that while I had it all apart I would just go ahead and replace them. I fit in the new floor pans and also began fabbing up a new trans tunnel. I built a trick little sheet metal brake out of some scrap steel to bend up the tunnel, nothing fancy but it worked shockingly well.







Removed the cab and finish welded the bottom.

[reg3]

After finish welding the floors and trans tunnel on the cab, I put the cab back on and checked the fitment. I am really happy with how the engine sits in the bay; plenty of room on both sides for steering/exhaust/intake. That tall engine looks pretty good in there!

[mongocanfly]

Welcome...looks like a great truck and a good plan...

[joedoh]

great fab work!

the 47-early 48 1/2 3/4 1 ton grilles are far and away my favorite AD front end, but they are HEAVY, readers take note of the big brace rods poking through the inner fenders.

[Purcell69]

Very nice work! One nice thing about these trucks is the vertical room that is available under the hood. That Cummins is a nice fit.

-Joe

[reg3]

Thanks for the kind words everyone.

Originally Posted by joedoh

the 47-early 48 1/2 3/4 1 ton grilles are far and away my favorite AD front end, but they are HEAVY, readers take note of the big brace rods poking through the inner fenders.

I couldn't agree more joedoh, they're pretty excellent looking but darn are they beefy.

[reg3]

Few more updates on the back half of the truck. The plan back here is to cut out/remove the existing axle, suspension and cross members and replace them with a newer ford 9-inch and a triangulated 4-link. I built a new higher clearance cross member with link mounts that will allow the driveshaft to pass through. Then fabbed up some c-notch plates that integrated into a smaller cross member that I plan to mount the airbags to. Now less words and on to the pics…

Cut out and removed all the old, then roughly put the new rear axle in place.



Built a new higher clearance cross member out of 2x4 steel with some gusset plates for good measure.







Welded in some link mounts to the new cross member.



And then built some links out of some 1-1/2" DOM steel, these things are beefy.



Cut out and installed some c-notch plates. They're a little deeper than I need but the bed already had to move up so I figured more room is better than less.



Mounted the axle in place to see where the truck sits when fully aired out. Depending on final tire size the axle will be a bit lower than pictured to lay the running boards on the ground when laid out.





Welded in the new notch plates and cut out the existing frame.





Fabbed in some link mounts to the axle housing. Finish welded everything and bolted it all together. It took a bit of time to get the adjustment just right, but I was able to get the axle located in the right spot and indexing up and down very smoothly. Really pleased with how it turned out.

[reg3]

Next thing on the list was getting the fuel and air tanks mounted. I decided to mount these on the back half of the frame behind the new c-notch/cross member. I picked up an RCI 20 gallon aluminum fuel cell. This size fit well between the frame rails. I welded in a new 2x4 rear cross member and fabbed up a little ‘cage’ to drop the fuel cell into. Its slightly overbuilt but I didn’t want any speed bumps turning the truck in to the next Exxon Valdez.

[8man]

Very nice work.

[mongocanfly]

Something tells me this isn't your 1st time....great work!!

[Dave_The_BMXER]

Wow this progresses fast!

[Purcell69]

Very nice fabrication work!

-Joe

[hobo]

Holy Crap! Talk about giving the rest of us incentive to get in the shop!

[reg3]

Thanks for the kind words everyone. Im heading down south for some sun and relaxation, so updates will be on hold for a bit. When i get back im turning to some steering routing. The plan is to keep the OEM steering wheel/column using a Column Saver kit from CPP. Its a pretty trick setup, pictures to follow.

[YahamaR1]

I LIKE IT.....
Real Nice work👍🏻

[Russell Ashley]

Very interesting build and nice fab work. It looks like you started with a solid truck. That's too bad about the accident but maybe lucky for you if that's why he sold it to you. Looking forward to following along.

[joedoh]

looking good!

[reg3]

I got some work done on the steering column and linkage. The plan here was to use the OEM steering column to keep the interior original and connect it to the new power rack. I ended up going with a Classic Performance Column Saver kit, it was a nicely made piece that was pretty easy to install. On to some pictures...

Cut the OEM column to length leaving some extra steering shaft that i will trim after installing the column saver



Then removed the column and installed the CP Column Saver (P/N: CP175BCS). I will be using 3/4" DD U-Joints, so i trimmed the steering shaft and cut in a DD profile to fit the u-joint.







Re-installed the steering shaft back in to the truck to start running the steering shaft to connect the column to the rack. I originally thought the run was going to pretty straight forward, but the darn starter is hanging out right in the path between the column and rack

[Nut Case]

Fun build, STRONG WORK, top notch welds. I like the over build touch. Over building is under rated!!!!!


Keep on keepin on

Nutz

[reg3]

Originally Posted by Nut Case

Fun build, STRONG WORK, top notch welds. I like the over build touch. Over building is under rated!!!!!


Keep on keepin on

Nutz

@nutcase couldn't agree more, thanks for the kind words.

I finished up running the steering shaft and as anticipated, the starter proved to be a bit tricky to work around. I tested out a few different routings but ended up running the shaft above the starter then dropping almost straight down to connect to the rack input shaft. This down-turn created a bit of a steep angle, so I ended up running a double u-joint just to be sure it turns smoothly.

It's a bit more complex than I had originally pictured in my head, but it turns as smooth as butter lock to lock and I am happy with the finished product.

I also installed a Classic Performance brake pedal bracket (P/N: 4753FBB). The fitment on this it was pretty excellent and real simple to install.





I also fabbed up a little bracket connecting the lower end of the OEM steering column to the fire wall.



Overall shot of the steering column/under dash. You can see the CPP Brake Pedal Bracket installed in this one (booster isn't connected to the pedal yet).

[8man]

Very nice work on that column.