1. home
  2. news
  3. features
  4. Custom Mercedes-Benz Unimog U500 Trail Rig

Custom Mercedes-Benz Unimog U500 Trail Rig

John Marshall’s 2005 Mercedes-Benz Unimog U500 is 80 percent unique trail rig and 100 percent custom machine

You might be currently thinking one of these three questions: "What is that thing?" or "Where do you take that thing?" or "What's in the back?" The short answers: John Marshall's '05 Mercedes-Benz Unimog U500 expedition camper; everywhere; and everything.

The Unimog in general still manages to give many people a case of the verklempts, simply because the vehicle has remained a rare breed to find on the trail (and on the street). But as John pointed out, the Unimog U500 is perhaps the most advanced and capable off-road vehicle ever made, with three locking differentials and three transfer-case ratios to select at the touch of a finger. First gear in low range is so low—at well over 4,000:1—it will move about 40 inches per minute at redline rpm.

With those kinds of impressive genes, why aren't we seeing more of them?

"They are not cheap and there are only a few people in the U.S. that can help when it comes to service," John says. To John's point, you'd be expected to cough up roughly six figures to buy one. The Unimog first arrived in Europe in 1951. But for this Unimog's timeline, it points to when Freightliner became the source for the German-built Mercedes-Benz U500, beginning in 2003. That ended about two years later. In case you didn't know, Unimog is short for universal motorized ger t. That third word has multiple acceptable translations, from machine to tool. Sounds about right for a Unimog.

 

Funny enough, this isn't John's first Unimog; he's fluent in 'Mog models. "They were like the Loch Ness Monster or Bigfoot. They were a mythical creature that everyone had heard about yet no one had really seen," he said. "After building the first truck, I was hooked." He's a garage-tinkerer for 30 years, so doing modifications on this Unimog was a non-issue. This self-taught fabricator has built houses, hot rods, 4x4s, and more, which means you won't find any aftermarket parts here. "My father was quite handy in the garage, but more importantly, he was also extremely cheap," John says. Therefore, I grew up learning to do whatever it took to get the job done. Yes, I'm too darn cheap to hire someone to do things for me."

Building a Unimog

John dedicated two years to this U500 project and said every day of the build had its challenges. "However, none of the challenges were too big to handle and without a hard deadline, I had plenty of time to overcome each one," he adds. Among the undertakings was going from a 216-inch wheelbase to 156 inches. "In its previous life, it was outfitted with a hook crane for delivering roll-off dumpsters in the Rocky Mountains and was originally built with a custom-length frame," John explained. "Yep, I shortened it by 5 feet!"

Custom Camper

He also built the entire camper from scratch, which now provides deluxe accommodations. It's approximately 7 feet wide by 7 feet tall by 12 feet long, and its weight was estimated to be 1,400 pounds empty. In terms of mounting it to the Unimog, John said, "I used the method that Mercedes-Benz has also used for many years. The idea behind it utilizes four sockets, one on each corner; however, you do not lock all four in. You only lock in two when you are off-road. Furthermore, it has a double-frame setup. The truck has its own frame, and then on top of that there is a secondary subframe, each of which has its own abilities to somewhat flex. The box mounts to the secondary frame, not the primary."

The volume of work to build the camper for this Unimog included making custom mounts and couplers, replacing worn-out rivets and installing additional ones for extra support, adding windows and doors, and doing all the wiring and plumbing.

Overlanding in a Unimog

John is an off-road trainer and guide by profession.

"I'm on the trail nearly seven days a week," he says. "And then when I go on vacation it is typically in the backcountry for weeks at a time. Some may say I have a problem!"

This lifestyle is one he's known since he was a child, he adds.

"I have told the story a thousand times to my friends, and it goes like this: Growing up, my mom and dad really didn't like spending much time together. And because of this, my dad took my brother and me camping at least three weekends per month. He had an old Ford van that was our chariot to adventure. Now they call this overlanding; I just call it my childhood." In adulthood, John and this Unimog can often be found on his favorite type of terrain, "a faded, dirt twin track that has been long forgotten and leads me to a place I've never been."

Unimog Optional Equipment

"I found these German trucks to be not only reliable, but extremely capable off-road," John says. "Air-ride seats, cruise control, engine and transmission braking, 46-inch tires, and so much more. The truck is stock, and stock kicks ass in the Unimog U500." His vehicle had been outfitted with every factory option available.

Transmission and VarioPilot Steering

We like how John tells it: "At the touch of a button, the truck can morph from an automatic transmission to a manual transmission. That is right—pull a lever and a clutch pedal will fold out from under the dash and it then shifts as a manual. It will also allow the operator to manually shift, and the truck will do all of the clutch work. Or, it will do all of the shifting as the operator does the clutch work." It also has VarioPilot quick-change steering. "The operator can pull a lever and slide the steering wheel and pedal assembly over to the right or left side of the cab and drive from either side of the truck."

Now, mix in an eight-speed transmission, plus the front, center, and rear locking differentials, and those three transfer-case ratios to your impure thoughts. Also, the transfer-case buttons have images to match what's going on: a rabbit equals high speed, working gears have a mule, and a turtle represents crawler gears.

Unimog Portal Axles

The front and rear portal axles are a trailing link/wishbone setup with hub reduction gear. John's all-wheel-drive Unimog has the 33,000-pound GVW rating (26,000 pounds was also offered), equaling a CGVW of 66,000 pounds. And there's a 60-gallon fuel tank—helpful, since we're talking approximately 10 mpg.

Suspension Upgrades

The 6.4L diesel engine is guesstimated to make 280-ish horsepower and nearly 1,000 lb-ft of torque. "This giant will cruise down the highway at 70 mph on its coil-spring suspension, as it lets you adjust the tire's air pressure on the fly with its central tire inflation system," says John. (And) this thing is tall; while driving it, I am looking down into semitrucks." That's right—it also gets street-driven.

Goodyear Military Tires and Hutchinson Wheels

John bolted on Hutchinson wheels to match the Goodyear military rubber. He also built a spare-tire mount using box tubing and angle iron, and a 3,500-pound ATV winch helps with access.

Solar Power

"All of my lighting is LED, and everything is working off 12 volts" John says. "I did want to have the added luxury of having a 110 AC system as well. The only appliance that I have that runs off of AC is the microwave. The four large AGM batteries that I have on this system are charged solely through the solar panels." On the topic of panels, he plans to expand the solar array. "I have a little over 500 watts on the roof now, and in the summer, that is more than enough. However, during the winter, the sun is far lower in the horizon, making the angle of incidence much lower as well. This lower angle drastically reduces the solar panels' efficiency. To date, the vehicle has never received a single electron from any other source other than the solar. But by expanding the array, I will also shorten the recovery cycle time for the system."

Expedition Camper

The expedition camper started as a Gichner military-surplus box, which John sandblasted, then rubberized the roof. Software typically meant for designing kitchens was utilized to blueprint the camper's interior layout, including areas for the bed, kitchen, and shower/toilet. Cabinets came from Home Depot, while items such as doors and windows, air conditioning, and appliances were found on eBay. He also built storage lockers accessible from the exterior.

Accessories and Comfort

Comfort and self-sufficiency while overlanding meant adding a three-way fridge; shower/cassette toilet combo; a kitchen with a sink, stove, and microwave; 84-gallon water tank; water heater; bed; entertainment system; flat-screen TV; AGM battery bank; 7,000-watt inverter; cell phone booster and antenna tower; LED lighting; and sofa. GPS is handled by Avenza and an iPad.

Custom Deck

Having a high-clearance vehicle meant the camper access would also be up high. "I have seen some builds that simply used a ladder to gain access. However, I felt this would be problematic." The door opens outward, so standing high enough on the ladder to reach the door would mean being in the way of the door. "I decided I would need some type of landing to stand on while opening the door," John says. "The porch was simply an expansion of this idea and the inspiration to build a full patio off the side of the camper." The 4-foot-wide porch is aluminum and decked in hard pine and operates via button-based hydraulics/linear actuators. Three receiver-hitch-style pieces are on the side of the box to hold the patio.

Specifications

General
Vehicle: '05 Mercedes-Benz Unimog U500
Owner: John Marshall
Stomping grounds: Moab, Utah
Build time: 2 years
Drivetrain
Engine: Mercedes-Benz OM906LA 6.4L inline-six
Transmission: Mercedes-Benz 8-spd EPS manual
Transfer case: Integrated with transmission
Low range ratio: 2.71:1
Crawl ratio: 3,165:1
Front axle/differential: Model 737.591 portal axle/locking differential
Rear axle/differential: Model 747.591 portal axle/locking differential
Suspension
Front: Coil springs, control arms, factory hydraulic shocks, steering stabilizer, pitman arm
Rear: Coil springs, trailing arms, factory hydraulic shocks
Tires/Wheels
Tires: 395/85R20 Goodyear MV/T
Wheels: 20x10 aluminum Hutchinson MRAP
Miscellaneous
Cool stuff: Steel receiver hitch, PTO, lightbar
Camper: Gichner box, rooftop solar panels, SMK Solar controller, 7,000-watt inverter, AGM battery bank, Carefree of Colorado awning, air conditioning, couch, custom deck/porch, entertainment system/TV, custom storage lockers, recessed lighting, shower, cassette toilet, kitchen with propane stove, woodgrain ceiling, Canyon Coolers cooler

More Videos