Komatsu GD405A-1(S/N 50002-UP)

The Komatsu GD405A-1 is a mid-size articulated motor grader from Komatsu's A-series lineage, with this listing covering the S/N 50002-UP production block of the A-1 generation, first built in the early 1980s. It runs the Komatsu 6D105, a mechanically injected 6-cylinder diesel displacing 6.5 liters and rated 82 kW (110 hp) net with 382 Nm of torque, from the pre-electronic era with no ECM or onboard diagnostics. Operating weight is 8,880 kg (19,577 lb), split roughly 2,550 kg on the front axle and 6,330 kg on the rear, riding a 4,900 mm wheelbase with a 3,100 mm moldboard and 440 mm maximum cut depth. Drive runs through a Hydroshift 6-speed forward/6-speed reverse power-shift transmission with 27-degree frame articulation. The A-1 followed Komatsu's earlier articulated grader lineage and was itself succeeded by later dash-number generations, GD405A-2 (S/N 1001-Up) and GD405A-3 (S/N 5001-Up), each starting its own independent serial run. Standard configuration includes drawbar-circle-moldboard blade control with optional scarifier (lift and body); rear ripper and snow-plow (V-plow) attachments exist at the broader Komatsu grader class level but are not confirmed specifically for this serial block.

Across the A-1, A-2, and A-3 generations Komatsu moved this grader family from purely mechanical fuel injection and controls toward electronically monitored engines and refined Hydroshift transmissions, with each dash-number generation resetting its own serial count rather than continuing sequentially from the last. The GD405A-1 sits at the mechanical, pre-ECM end of that lineage: simpler to diagnose and repair in the field, but tied to parts specific to the 6D105 mechanical injection pump and the A-1 chassis rather than later electronic fuel systems. Because large numbers of these graders remain working on secondary roads, mine haul routes, and municipal fleets decades after leaving the factory, well-documented used units and their driveline, hydraulic, and undercarriage parts stay in steady demand in the used equipment and parts market.

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.