1998–2007 Komatsu PC78UU-6 / PC78US-6 Excavator Service & Repair Manual (P/N SEBM025116)

This Komatsu shop manual, publication SEBM025116, October 2007 edition, covers 1998–2007 PC78UU-6 and PC78US-6 hydraulic excavators. Coverage starts at PC78UU-6 S/N 22832 and PC78US-6 S/N 4001, with a dedicated Norway/EU section for PC78US-6 S/N 4809 and up.

• Engine and cooling: Engine, injection-pump, and cylinder-head removal and installation; compression testing, valve-clearance adjustment, injection timing, and radiator and oil-cooler service.

• Hydraulic diagnosis: CLSS operation, LS differential-pressure testing, PC valve adjustment, PPC pressure checks, hydraulic-drift diagnosis, motor-leakage testing, and circuit bleeding.

• Travel, swing, and undercarriage: Travel-motor and swing-machinery disassembly and assembly, idler and recoil-spring service, track-roller repair, and track-tension checks.

• Work equipment: Hydraulic-cylinder rebuilding, boom and offset-bracket removal, multi-control valve operation, and PC78UU-6 interference-prevention system diagnosis.

• Electrical troubleshooting: Controller and monitor fault charts, connector arrangement diagrams, connector-pin tables, wiring diagrams, and TVC-EPC and governor-control diagnostics.

• Configuration differences: Blade-equipped and blade-less hydraulic systems, steel-shoe, road-liner, and rubber-shoe configurations, plus Norway/EU anti-burst valve and overload-alarm documentation.

Written for service technicians carrying out workshop repairs, the manual includes procedures requiring hydraulic test equipment, dedicated adapters, presses, and lifting equipment.

Engine Testing, Removal, and Cooling Service

Engine coverage includes performance and fuel-consumption specifications for the 4D95LE-2 and S4D95LE-3-A, along with compression, blow-by, oil-pressure, and injection-timing checks. The repair section describes injection-pump and cylinder-head removal and installation, plus removal of the engine and main pump.

Engine scope: Detailed engine information is assigned to the separate 95-2 Series and 95-3 Series Engine Shop Manuals. Those publications are not included in this PDF.

Cooling-system layouts accompany radiator and hydraulic oil-cooler removal procedures. Fluid tables distinguish specified capacities from refill quantities and identify hydraulic-system and cooling-system changes at PC78US-6 S/N 6501.

CLSS Diagnosis and Hydraulic Repair

The CLSS section explains how LS differential pressure controls pump swash-plate angle. Its testing procedures cover LS and PC valve adjustment, control-circuit pressure, and PPC valve output. The LS test identifies differential-pressure gauge 799-401-2701 among the required instruments.

The hydraulic-drift test distinguishes cylinder leakage from control-valve faults, helping identify which assembly needs further inspection. Separate procedures address swing- and travel-motor leakage, control-valve removal, and center swivel joint removal and installation.

Eight hydraulic circuit sheets distinguish the blade-less, blade-equipped, additional-attachment, Norway/EU, and PC78UU configurations. The bleeding instructions warn that an empty pump case or trapped air between the pump and hydraulic tank can cause overheating and pump damage.

Follow the manual’s hoisting, work-equipment support, and residual-pressure precautions when handling heavy assemblies or opening hydraulic circuits.

Travel Drives, Swing Machinery, and Work Equipment

PTO and power-train layouts show the connections between the engine, pumps, travel motors, and swing system. The GM09VN2 travel-motor repair section includes an assembly sectional drawing, an exploded reduction-gear drawing, parts lists, inspection limits, clearance-adjustment tables, and a performance test.

The travel reduction gear’s reamer bolts can seize because of adhesive in their threaded holes; the disassembly section addresses this specific risk.

Swing-machinery procedures cover the reduction gears, shafts, bearings, and seals. Undercarriage coverage includes track frames and idler cushions, while working-range drawings and work-equipment dimensions accompany boom, offset-bracket, and cylinder service information.

Monitor Diagnostics and Norway/EU Systems

The monitor section distinguishes user codes from stored service codes, including E02 for the TVC-EPC system and E05 for governor control. Diagnostic charts connect symptoms and codes with wiring, relay, sensor, and controller checks.

Serial-specific connector maps and electrical circuit diagrams help technicians select the correct circuit before tracing a fault. PC78UU-6 coverage includes angle sensors, interference prevention, and depth indication.

The Norway/EU section adds boom hydraulic anti-burst valve information, overload-alarm pressure sensing, meter-display functions, and the associated troubleshooting circuits.

Standard metric bolt, flared-nut, split-flange, and O-ring boss-joint torque tables supplement the component procedures. Maintenance standards provide wear limits, while lubricant and capacity tables cover the engine, swing machinery, final drives, and hydraulic and cooling systems.

A Preview of Valve-Clearance and Track-Tension Data

These engine and undercarriage settings are a small selection of the adjustment data in the manual.

For both covered engine builds, the standard valve clearances at normal temperature are 0.35 mm for the intake valves and 0.50 mm for the exhaust valves.

Track-tension specifications distinguish 10–30 mm of slack for road liners or steel shoes from 1–3 mm for rubber shoes. These values refer to the maximum gap between the track top and the underside of a straightedge spanning the idler and carrier roller.

PDF Search, Bookmarks, and Diagram Detail

Text search and diagram navigation: The service text is searchable, although many labels within circuit diagrams are not included in text search. Embedded bookmarks provide access to chapters and individual procedures. Small wiring labels, pin numbers, and wire codes require zooming.

Supplied as one printable, English-language, 1,027-page PDF. The total includes the integrated 109-page Norway/EU section, the original cover and revision lists, and three blank pages.