1990 Dodge Truck – Ultimate Tug-Truck: Part 3

Our burly Dodge Tug-Truck is getting closer to trail-ready after another month of work under its belt—belt line, that is. This is the retired military Dodge airplane tug that we are reissuing as this year’s official truck of the Ultimate Adventure 2014, since so many readers begged for a return to an old iron off-roader. The Dodge has been under the scalpel at Pacific Fabrication, and we’re hustling to get it back up and running. The further we dive into this project, the more work we find it needs, but lucky for us we started with a pretty rust-free specimen and we have a quality fab shop on the job.

A word about the Pacific Fab team. They are really known for their GM LS-engine swaps into both 4x4s and hot rods of all makes and models, but after we had gone there years back for Dumpster, our Dodge M37 project, we knew Pacific Fab was more than capable of this Frankenstein mobile. Yes, it has a Cummins diesel under the hood and not a fire-breathing GM V-8, but the rest of the build is mostly custom fabrication and just requires solid building skills, which Pac Fab is great at.

As with any project, we had hoped to be further ahead. We wanted to tell you about the suspension this month, but we opted to start with some solid rock sliders, and that snowballed into boxing the entire frame for additional strength. All this work while the drivetrain is out will give us a longer-lasting Tug-Truck for years to come.

The Tug-Truck has some low-hanging rocker panels, which are fine when dragging planes around the tarmac but not ideal for a week of rockcrawling and trail bashings. This sheetmetal hangs almost 3 inches below the doorsill.

We buzzed away the rockers with a plasma cutter and then ground them smooth to be flush with the bottom of the door. This will give us some clearance, but even better, it will allow us to build rock sliders that don’t hang down below useless sheetmetal.

The military trailer bed of our truck has a very square look, and so does the first-gen Dodge sheetmetal, so we followed that through to the rock sliders and built them from 2×4 rectangular tubing.

The rock sliders tubing is 1⁄4 inch thick under the door where the majority of abuse will occur and then 1⁄8 inch thick up along the bed. We added rectangular tube kickers to attach to the frame.

The rock sliders stick 6 inches past the bed before replicating the bed wheel opening angle up to the lower bedrail. We added a patch of expanded metal to that gap so it can work as an easy step for accessing the front of the bed.

We like how the rear of the frame is almost flush with the back of the bed, and without a big rear bumper the tailgate can be opened 180 degrees. The Pac Fab team added a stick of 2×2-inch square tube under the bedrail and added a piece of 2×4 out at the ends to run under the rear corners of the bed. Additional 2×2 gussets run to the frame, but we still need to add taillights, recovery points, and corner caps too.

After adding the rock sliders we noticed they moved a lot when we tried lifting the truck with them. We added a 2×2 crossmember above the frame from one rock slider to the other that runs under the bed. Then we decide to go a step further and box in the entire frame. These old Dodges have an open C-channel frame, which is as floppy as a fish out of water. Jason Howerton started by making a cardboard template of the frame.

Next, Howerton copied the outline on a sheet of 1⁄8-inch (0.125) steel. The frame is currently 3⁄16 inch (0.188), but the 1⁄8 will be enough to help make it more rigid without adding more weight than is necessary. We considered hole-sawing and dimple-dying the plate for even more strength, but that was deemed superfluous work at this point.

We tacked the plates into place and then brought the frame down off the lift and onto jackstands to be sure it was level and square before welding. Then when we did weld it, we stitched it and jumped around from side to side letting it cool and measuring it to be sure it didn’t pull or move. We will eventually add to the front section and maybe pull the Cummins completely out to finish the frame.

As we were moving forward on the frame, a special package arrived with our new transmission. We approached the guys at Rockland Standard Gear about an NV-4500 five-speed manual for Tug-Truck, and they turned us onto a new five-speed, the Tremec 4050. This is a transmission still in production (unlike the NV-4500) and made as a replacement. However, it uses an all-aluminum case with substantial ribbing for a light but strong gearbox. It has a 6.16 First gear and a 0.24 overdrive Fifth gear, and uses standard Dexron ATF instead of gear oil or the expensive lube required for NV-4500s.

Rockland Standard Gear got us what may be the first Tremec 4050 in use in the United States, so we’re definitely treading new ground. Rockland believes that this transmission will be a perfect fit for trucks, Jeeps, and most standard diesels. We’ll be hot-rodding our Cummins slightly but nothing extreme, so it should be fine. We bolted an Advance Adapters bellhousing to the gearbox, but had a small issue with one of the four mounting holes being off on the transmission. We simply drilled a new one and everything fell into place.

The output shaft on the Tremec 4050 is a 23-spline version, so we will need to match that with our Magnum 205 transfer case from Offroad Design. The circular six bolt pattern on the back of the Tremec is standard for ease of assembly.

We started mocking up a custom upper axle truss for our front Dynatrac ProRock 80 but stopped midstream when we decided to box the frame. Since the frame suspension mounts will need the frame boxed first, we want to get our transmission and transfer case in before we lay out our front links so we can verify that the driveshafts and links will clear items like the bellhousing and starter.

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