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One Man's Duramax Suburban

Posted in Project Vehicles on July 8, 2004 Comment (0)
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Can you tell this rig wasn't built by the factory? Visually and functionally, this is pretty much what you'd get from GM. Maybe better. Early rumors suggested that the factory Duramax rigs would be detuned versions with about 250 ponies. Not this one. It cranks out the full 300 hp and 520 lb-ft.

Many of us have been frustrated at not being able to get a particular combination of features in a new truck. It's not something that generally causes lack of sleep, hair pulling or alcoholism, but here we sit, with a pocketful of cash, waiting for a particular setup we are told will soon appear, and...nada. Well, just like the vigilantes of the Old West, sometimes a man's just got to take things into his own hands. Bill Armstrong is such a man. A farmer near Wauseon, Ohio, Armstrong has long been a fan of GM diesel-powered trucks or SUVs and has converted older GM trucks and Suburbans to diesel. When the new Duramax appeared, he was well and truly smitten, but had his heart set on a Duramax-powered Suburban. The rumor mill hinted that a Duramax-powered Sub was due soon after the pickups, but three years later, Bill was still unfulfilled.

Since leaving the sport of truck pulling, Bill has stayed busy building or rebuilding cars and trucks in his well-equipped shop. During the dog days of winter, and between farming tasks at other times, he can generally be found putting some rig together for resale or personal use. When he got to looking at the late-model GM trucks one non-farming day, he realized that it was possible, if not relatively easy, to build a Duramax-powered Sub of his own.

Looks stock to us, just like a factory Duramax Suburban would look. The best part is that all the new hop-up goodies out there could turn this Suburban into a nine-passenger rocket.

Armstrong noted that the chassis on all the 2500 and 3500 series GM trucks and SUVs were very similar within their types. The biggest differences are found in their front sections, and they revolved around things like engine mounts and such. A little detective work yielded the fact that their chassis are built in two pieces--the front, which is designed for whichever engine is selected, and the rear, which is pretty generic among the vehicle type (i.e., pickups or SUVs). The factory simply matches the front section for a type of engine with a rear section for a specific type of body to make the basic platform.

Armstrong acquired a rolling '02 Duramax 2500HD truck chassis, complete with drivetrain; a bare '02 Avalanche chassis and a complete '02 Suburban 1500 body. He put the front section of the Duramax chassis onto the Avalanche chassis and installed the Suburban body onto it. It sounds simple, but there were many small complications. Here are a few.

This is the point where the front and rear chassis sections are welded at the factory. Bill carefully unzips the pieces for his mix-and-match job. Getting them apart without damage requires some care. If you look at Bill's job and the factory job, you can't see much difference. Bill built a special jig for lining up the sections.

Because the Duramax trucks have a much higher radiator support to accommodate their honkin' big radiator and intercooler, Armstrong had to use the front wrap from a diesel pickup. This required him to use body-lift pucks to raise the Suburban body up to match, about 2 inches. Because there was a nasty gap in the rear below the cargo area doors and bumper, he had to custom build a valance to hide it. Because the body was a 1500HD rather than a 2500, there were also some minor adaptations necessary to the body mounts.


Because the Suburban body had to be lifted 2 inches to match the height of the front end, a valance was necessary for cosmetic purposes to hide the gap created between the bumper and the floor. Can you spot it?

There were other complications. Because the diesel uses by-wire electronic throttle control, the body used must have this equipment installed. It can be retrofitted and comes standard with 8.1L trucks and SUVs. The various body and engine control modules must communicate with each other, and because they came from different trucks, a trip to the GM dealer for programming was necessary when everything was hooked up. Armstrong has learned that sometimes you plug everything in and the trucks run normally. Sometimes, the modules won't talk. This results in limp-mode operation. Either way, Bill takes the precaution of a dealer visit. Diesels also require Hydroboost power brakes, which necessitated another retrofit. Armstrong reckons that a 2500 Sub body would have been more of a bolt-on, and if it were a 2500 with an 8.1L, it would have had Hydroboost and an electronic throttle.

The chassis was then given all the rest of the 2500HD truck's drivetrain, including the 11.5-inch American Axle rear axle and springs. It all bolted up, though Armstrong had to relocate the transfer case mounts--just a simple drilling job. Because everything was '02 vintage, Armstrong was able to find matching colored parts and there was absolutely no painting or bodywork in the conversion, other than building the previously mentioned rear valance.

Bill Armstrong at work on is current project, building a Duramax-powered Crew Cab from parts. The parts are already stacked up for the next job, a Duramax Avalanche.

So how does it drive? Just like it was a factory rig. It's everything GM should offer but doesn't. After driving it, you'll wonder why. It's powerful, fast and can pull a house. What's not to like? The fuel mileage is somewhat better than a pickup, due to improvements in aerodynamics. Bill reports an honest 20 mpg on local rural roads and recently towed a 24-foot trailer cross-country with 16mpg economy. When asked if the Dura-Sub will light up the tires, he just smiled. So what's the bottom line on the conversion? Armstrong says, "I don't know if anything in the conversion was particularly hard, but it did require a lot of research." On hearing that, a person must realize that "easy" to a talented fabricator with lots of experience building trucks from pieces might be a nightmare to the rest of us.

As for bucks, Armstrong reckons he can build diesel Subs for $10,000 to $15,000 less than a new high-end Duramax pickup (which is probably cheaper than the mythical factory Duramax Sub would be; figure about $50K for one), while using new parts that come from damaged-in-shipment vehicles that are sold for salvage by the factory without ever having been registered. As to practicality, on one hand you get something basically new that you can't get anywhere else (yet), and get it cheaper. On the other, you have no warranty and a salvage title. What's next for Bill Armstrong? Local interest in his Dura-Sub has prompted a few people to make orders. He's also converting a few late-model gas pickups to Duramax configuration, but he is also planning to do a Duramax Avalanche and we'll keep you posted about that. Yes, Bill will entertain orders for a Duramax Suburban or Avalanche.


Bill Armstrong
Wauseon, OH 43567


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