Komatsu D20P-7A, D20PL-7, D20PLL-7, D20AG-7, D20PG-7A, D21A-7, D21AG-7, D21S-7, D21QG-7, D21PG-7A Bulldozer Shop Manual (P/N SBM001407)

• Official Komatsu publication SEBM001407, dated December 2000, supplied as a 668-page PDF. Cover coverage starts at D20PL-7/D20PLL-7 serial 62001; D20AG-7, D20P-7A, D20PG-7A, D21A-7, D21AG-7, D21PG-7A, and D21A-7T serial 75001; and D21S-7/D21QG-7 serial 61001.
• D20 repair coverage includes the wet multi-disc main clutch and 3F/2R sliding-mesh transmission, with removal, internal disassembly, assembly, control-linkage adjustment, and maintenance limits.
• D21 sections handle both F2/R2 and F3/R3 hydroshift transmissions, including the transmission pump, control valve, modulating valve, selector/inching valve, pressure tests, linkage setup, and inching-pedal adjustment.
• Steering and undercarriage work covers PPC controls, steering clutches and brakes, the bevel-gear shaft, final drives, track frames, recoil springs, idlers, rollers, track shoes, and rubber-crawler configurations.
• Hydraulic repair material addresses the pump, main relief and control valves, work cylinders, circuit pressure testing, drift diagnosis, bleeding, and straight-tilt, power-angle/tilt, and dozer-shovel work equipment.
• Diagnostic support includes engine and chassis symptom charts, serial-specific electrical wiring diagrams, power-train and work-equipment hydraulic schematics, monitor circuits, sensor checks, section views, and exploded assembly drawings.

Prepared by Komatsu as a service-workshop repair aid, this manual is best suited to technicians who already understand heavy-equipment service practices and have access to proper lifting, hydraulic-test, and precision-measurement equipment.

Model and Serial-Specific Differences

A major serial break changes the main engine from the 4D95S-1 to the 4D94E-1A: D21A-7 and D20P-7A at serial 78604, D21S-7 at 61132, and D20PL-7/D20PLL-7 at 62454. The corresponding sections change the engine-control arrangement, starting and charging hardware, fuel-injection-pump and cylinder-head procedures, sensors, and wiring coverage. The D21A-7T trimming-dozer section follows a separate 4D95L-1/4D98E-1A split at serial 78604.

The D21 hydroshift material documents F2/R2 and F3/R3 configurations across the covered production ranges; it is not presented as a simple early-to-late conversion to F3/R3. Serial-indexed pages distinguish the control linkages, while the F3/R3 coverage includes the mechanism that prevents a start in third gear.

Testing, Troubleshooting, and Shop Data

Engine checks cover speed, exhaust color, valve clearance, compression, blow-by, injection timing, oil pressure, and fuel-system bleeding. Chassis procedures include power-train pressure measurement, PPC-valve adjustment, work-equipment relief testing, steering and cylinder bleeding, and clutch, transmission, inching, and brake linkage adjustments.

Komatsu’s tool tables identify equipment such as multi-tachometer 799-203-9000, hydraulic tester 799-101-5001, unit repair stand 790-501-5200, and recoil-spring compressor 791-685-8005. Standard-value and maintenance tables provide component torque specifications, pressure-test data, capacities and approved lubricants, adjustment dimensions, wear limits, and electrical test criteria.

Troubleshooting is divided into S-mode matrices for 16 engine symptoms and H-mode charts for 32 hydraulic or mechanical complaints. These cover starting, output, overheating, oil pressure, travel and steering faults, shift delay or shock, blade performance, cylinder drift, and dozer-shovel bucket operation.

Diagrams and Repair Depth

Named visual references include the D20 and D21 power-train skeletons, separate F2/R2 and F3/R3 power-train hydraulic circuits, straight-tilt and power-angle/tilt work-equipment circuits, the D21S/QG dozer-shovel circuit, serial-specific machine wiring diagrams, and cab monitor and sensor circuits.

This is primarily a chassis shop manual. It includes engine testing plus removal and installation of the injection pump, cylinder head, radiator, and complete engine, but it does not provide a full internal engine overhaul chapter. Komatsu’s volume note states that separate engine, electrical, and attachment volumes may be needed to cover every repair. Section 90 adds D21A-7T trimming-dozer specifications, structure, wiring, and maintenance standards; shared procedures remain in the main D20/D21 chapters.

Two cautions show the level of assembly detail. The work-equipment valve chapter warns that disassembling the dump/tilt-back safety-and-suction valve changes its preset pressure, which cannot be readjusted after reassembly. The transmission chapter also warns that treating the cage forcing screws as general pullers can damage the cage; their use is limited to extracting adjustment shims.

The procedures involve stored hydraulic pressure, compressed recoil springs, track separation, and heavy assemblies. Follow the manual’s blocking, pressure-release, hoisting, and shop-safety requirements before beginning repair work.