Doomsday Diesel is a ’91 GMC Suburban 2500 that began life with a gas engine. Now it has a ’95 12-valve Cummins built by Industrial Injection between the framerails. Doomsday Diesel is a ’91 GMC Suburban 2500 that began life with a gas engine. Now it has a When building a diesel truck you want to last, less is always more. Less plastic means more steel, fewer electronics means more reliability, reduced options means more capacity, and zero spark plugs means more power and fuel economy. Mercenary Offroad’s Todd Farrand pulled the engine and TCI 6X (based on a GM 4L80E) so he could modify the pan. Mercenary Offroad’s Todd Farrand pulled the engine and TCI 6X (based on a GM 4L80E) so he When we began our 5.9L Cummins-powered Doomsday Diesel project back in the January ’12 issue, we knew we wanted a low-tech truck that would be too simple to fail, yet easy to fix if it ever stopped running. We didn’t anticipate we’d be replacing or rebuilding everything that spins or holds fluid on this ’91 GMC Suburban —but that’s what we’ve done. As you can imagine, it’s taken us longer than we expected. Why have we gone this far? Well, building a vehicle that will function through the apocalypse required an assembly of parts that we could be certain wouldn’t fail. The best way to gain that certainty was to inspect each critical component. The systems deemed worn out were rebuilt, those pieces seen as weak were upgraded, and the creature comforts discovered to be unnecessary were removed. We planned to keep the Suburban’s original vacuum brake booster and master cylinder, but in order to get the most out of our new four-wheel EBC disc brakes, and to make sure the injection pump won’t hit the master cylinder (arrow), we’re ditching it in favor of a Hydroboost system. We planned to keep the Suburban’s original vacuum brake booster and master cylinder, but i When Doomsday Diesel is complete, we expect to have an all-terrain vehicle with a 1,000-mile fuel range, seating for four, and virtual (if not actual) bulletproof durability. The true test of this machine will be an escape from Los Angeles scenario, in which we see what it really takes to escape this booby-trapped metropolis after society crumbles. Or we’ll just try to drive out of town on the Friday afternoon before Labor Day weekend. With the Cummins swapped in and a Dynatrac ProRock Dana 60 front axle in place, we found the oil pan and pinion yoke could connect when the suspension is twisted up (arrow). With the Cummins swapped in and a Dynatrac ProRock Dana 60 front axle in place, we found t Farrand then cut the oil pan open and painstakingly trimmed the pan back to gain as much front driveshaft clearance as possible. He took care not to encroach on the Cummins’ oil pickup tube and made sure to clean the pan of all grinding dust before test fitting it to the engine. Farrand then cut the oil pan open and painstakingly trimmed the pan back to gain as much f When he was happy with the clearance gained, Farrand TIG-welded the pan closed using a piece of sheetmetal he fit in place. The welds were then tested for leaks by filling the pan with water. When he was happy with the clearance gained, Farrand TIG-welded the pan closed using a pie We wanted to use a ’99 to ’10 Super Duty NV 271 transfer case, but it wouldn’t fit between the Sub’s framerails. We opted for this BorgWarner 4470 (used in ’96 to ’00 1-ton GM chassis-cab trucks) that Rockland Standard Gear built us. Rockland has experience with all kinds of 4x4s, from snowplow trucks to off-road race trucks, and it deemed its Tranzillia gearbox up to the task. We like the BW 4470 because it offers a 1410 fixed-yoke rear output, PTO capability, and pressurized lubrication. We wanted to use a ’99 to ’10 Super Duty NV 271 transfer case, but it wouldn’t fit between To mate the TCI 6X 4L80E to the BW 4470, we used the cast-iron GM transmission adapter that came with our Suburban and an Energy Suspension urethane mount. This truck was built with a passenger-side transfer case front output, but bolting the driver-side drop 4470 in place gained exhaust and driveshaft clearance. All we had to do was flip the factory crossmember around and drill a new hole in the truck’s frame. To mate the TCI 6X 4L80E to the BW 4470, we used the cast-iron GM transmission adapter tha The power take-off (PTO) feature adds about 6 inches to the length of the transfer case, which caused the BW 4470 to contact the floor of the Suburban. To make more room, we added Offroad Design’s complete 1-inch body lift and a new set of Energy Suspension urethane body mounts. The urethane mounts are Energy Suspension’s trademark red, but we took Offroad Design’s billet-aluminum body lift blocks and had Prime Plating hard anodize them to prevent wear and corrosion. The hard anodizing process turns most machined aluminum a dark gray color. The power take-off (PTO) feature adds about 6 inches to the length of the transfer case, w By replacing the body mounts with new urethane pieces, we’ll be able to align the doors and fenders with their original specs. The Offroad Design 1-inch body lift on top of the urethane will give the truck valuable room for the 37-inch tires we plan to run. By replacing the body mounts with new urethane pieces, we’ll be able to align the doors an Tuning the vehicle’s ride height is going to be tricky until we finish assembling Doomsday Diesel. We began with the factory two leaf springs (front), but they couldn’t handle the extra weight of the Cummins, and the suspension bottomed out just sitting in the shop. Next, we ordered a set of Rancho’s 4-inch-lift, five-leaf, RS 86206 springs (rear) with a spring rate of 560 pounds per inch (ppi). We also tracked down a set of discontinued Rancho RS 40054S springs (middle)—which has 672 ppi—for sale on Amazon.com in case the front end gets too heavy. Tuning the vehicle’s ride height is going to be tricky until we finish assembling Doomsday The leaf-spring suspension is a proven technology that’s been around since the horse-drawn wagon. While the springs themselves rarely ever fail, the bushings that attach them to the vehicle take a beating. Fortunately for ’73 to ’91 GM truck owners, Offroad Design has removed these weak links from the truck with its greasable urethane spring bushing kit. The biggest increase in durability comes from its heavy-duty Front Upper Shackle Hanger kit. These new pivot points replace the factory 1 1⁄8-inch frame pivot bushings (bottom) with massive 1 1/2-inch pieces (top)— virtually ending front bushing wear. The leaf-spring suspension is a proven technology that’s been around since the horse-drawn Installing Offroad Design’s Front Upper Shackle Hanger kit required us to drill out some rivets in the frame and then use a hole saw to enlarge the openings. Installing Offroad Design’s Front Upper Shackle Hanger kit required us to drill out some r The Offroad Design Front Upper Shackle Hanger kit was then bolted in using Grade 8 hardware. We also upgraded the front with Offroad Design’s heavy-duty zinc-plated shackles to replace the thin stamped-steel factory versions that can bend from extreme use. The Offroad Design Front Upper Shackle Hanger kit was then bolted in using Grade 8 hardwar To dampen the 520-ppi-spring-rate, 4-inch-lift Rancho leafs, we stepped up to dual Rancho RS 9000 XL adjustable shocks using upper Quad Shock mounts from LMC Truck (arrow). Using dual adjustable shocks will let us tune the ride to be soft—while still having enough capacity to prevent the shocks from fading. To compensate for the suspension lift, we fitted Offroad Design’s extended brake lines to the front of the truck. These DOT-brake lines feature a Teflon inner core wrapped in a layer of Kevlar braid, a layer of stainless braid, and then the protective outer vinyl shield. To dampen the 520-ppi-spring-rate, 4-inch-lift Rancho leafs, we stepped up to dual Rancho Changing the suspension’s ride height meant we’d also have to correct the Suburban’s steering geometry. Offroad Design’s crossover steering kit allowed us to use a heavy-duty draglink to connect a two-wheel-drive steering box to an ORD’s high-steer arm mounted on the passenger-side Reid Racing steering knuckle. Then a 1 1/2-inch-diameter tie rod was used to connect the two steering knuckles. Greasable tie-rod ends were used instead of rod ends for the longest possible service life. Changing the suspension’s ride height meant we’d also have to correct the Suburban’s steer Since we added a 1-inch ORD body lift, had to change the steering box, and just didn’t trust the 21-year-old factory steering shaft, we bolted in this Borgeson telescoping steel steering shaft. It features two billet-steel U-joints to provide smooth steering action and eliminates the rubber coupler used by the factory steering shaft that can deteriorate over time. From this angle, you can also see the Hydroboost brake booster (from a ’91 6.2L diesel Suburban) and the brake master cylinder (from a ’96 GMC P-30 Step Van) that we’ve tied into the Sub’s brake system using LMC Truck’s complete stainless-steel brake line kit. We’re still dialing in the brake hardware, so check back next month to see our final combination. Since we added a 1-inch ORD body lift, had to change the steering box, and just didn’t tru We had Lee Manufacturing rework our Saginaw power steering box for extreme use. Tom Lee builds these boxes to aerospace-specs, and he fitted ours with a billet upper sector shaft cover, a two-wheel-drive sector shaft (to allow us to use crossover steering), and modified the box to control a remote ram assist. We had Lee Manufacturing rework our Saginaw power steering box for extreme use. Tom Lee bu We’ve used Hutchinson two-piece, double beadlock wheels on many of the vehicles we’ve built. For this project, we’re reusing a set of 17x8 1/2-inch billet-aluminum Rock Monster wheels we’ve had since 2002. These wheels are rated for 3,850 pounds each, use steel wheel-lug inserts, and were originally powdercoated silver. For this build, we disassembled the wheels, had the powdercoating chemically stripped, and had the wheel faces polished. We’ve used Hutchinson two-piece, double beadlock wheels on many of the vehicles we’ve buil We then sent the wheels to Prime Plating, where they were given a Type III hard-anodized finish (mil-spec-A-8625). This finish is similar to what can be found on high-end cookware and provides an abrasion- and chemical-resistant matte-gray surface that’s literally part of the wheel. We then sent the wheels to Prime Plating, where they were given a Type III hard-anodized f There’s no other tire on earth that has the survivability track record of the BFGoodrich Baja T/A. This is the tire that’s won the grueling Baja 1000 off-road race more than any other—and it’s the ultimate 37x12.50R17 zombie-crushing tool. There’s no other tire on earth that has the survivability track record of the BFGoodrich B SOURCES Energy Suspension 1131 Via Callejon San Clemente 92673 888-913-6374 www.energysuspension.com Reid Racing 1917 Oak Park Blvd. Pleasant Hill CA 94523 925-935-3025 http://www.reidracing.biz/ Rancho Suspension 1 International Drive Monroe MI 48161 734-384-7804 www.gorancho.com Mercenary Off Road Sun Valley CA 91352 www.mercenaryoffroad.com Rockland Standard Gear 150 Route 17 Sloatsburg NY 877-774-4327 www.rsgear.com TCI Auto 888-776-9824 www.TCIAuto.com LMC Truck 15450 W. 108th Street Lenexa KS 66219 800-562-8782 www.lmctruck.com Hutchinson 250 Ewing Street Trenton NJ 08609 609-394-1010 www.rockmonsterwheels.com Dynatrac 7392 Count Circle Huntington Beach CA 92647 714-596-4461 http://www.dynatrac.com Off Road Design 970-945-7777 offroaddesign.com/ Borgeson Universal 91 Technology Park Drive Torrington CT 06790 860-482-8283 www.borgeson.com Lee Power Steering 818-768-0371 http://www.lee-powersteering.com Industrial Injection 1201 South 700 West Salt Lake City UT 84104 800-955-0476 www.industrialinjection.com Prime Plating www.prime-plating.com BFGoodrich P.O. Box 19001 Greenville SC 29602 877-788-8899 www.bfgoodrichtires.com By David Kennedy Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!