Caterpillar D550B

The Caterpillar D550B is a six-wheel-drive (6x6) articulated dump truck built in the mid-1980s, around 1986-87, during the early Caterpillar/DJB Engineering partnership centered on DJB's plant in Peterlee, England. It sits at the top of that early Cat-badged articulated-truck range, in the nominal 50-55 tonne payload class, well above the 36-tonne D400 that Caterpillar introduced as its first Peterlee-built ADT in 1985. Power comes from the Cat 3408 V8 diesel, an 18.1-liter engine with all-mechanical unit injection and no electronic controls, feeding a powershift transmission and a six-wheel-drive transfer gearbox with front-axle disconnect for two- or six-wheel drive. Steering is by articulated-frame hydraulics, and hydro-pneumatic struts front and rear cushion the ride. Caterpillar tracked the whole model under a single serial prefix, 5ND, consistent with a short, low-volume production run rather than a mainstream multi-year program. Exact body and drivetrain configuration options for this specific model are not documented in surviving public sources; the wider D-series range it belonged to was also built as pipe-carrier, log-carrier, and quarry-hauler derivatives, though it isn't confirmed which, if any, of those variants reached the D550B.

The B suffix marks Caterpillar's own production version, following its 1984 purchase of DJB's articulated-truck design rights, as distinct from any earlier DJB-branded prototype. A 55-tonne-class articulated hauler proved too niche for the market; rigid haul trucks handle that payload range more efficiently than an articulated frame, and Caterpillar dropped the D550B after a short run rather than replacing it in kind. The ADT range that followed settled into a lower 25-40 tonne band, and today's largest Cat articulated truck, the 745/745C, tops out around 41 tonnes on a completely different C18 ACERT engine. That gap makes the D550B one of the rarest Cat-badged haul trucks still in the field. Few were built, factory documentation predates Caterpillar's digital publication era, and most surviving units carry no verified service history. For today's used and parts market, that scarcity cuts both ways: finding a running example is hard, but the D550B's Cat 3408 engine and powershift driveline are shared with far more common Cat machines of the same period, so parts sourcing generally runs through that broader engine and driveline family rather than model-specific stock.

Below: full specifications, fluids & capacities, the factory service schedule, common service parts, verified fault codes, what owners discuss, attachment guidance, the complete assembly directory, and a serial-number reference. Complete parts lists with full OEM part numbers, exploded diagrams, quantities, and fitment data are available free in Heavy Parts AI.