Description

Komatsu PC78US-6, LPD45 Technical Manual

You are staring at a hydraulic pump that looks like a plumbing nightmare. Ports labeled everything from P1 to PEPC. You need the torque for that plug before you snap it off. The aftermarket PDF you obtained last week gave you a generic range that didn’t match the casting. That’s why you stop wasting time on guesswork and get the real thing: the Komatsu PC78US-6, LPD45 Technical Manual. 123 pages of factory-sourced structure, function, and maintenance standards – not reprints of reprints.

Every time I see a tech reach for a third-party handbook I cringe. Those books borrow specs from a completely different pump model and call it “universal.” This manual came off the same Komatsu server that the dealerships use. It covers serial number ranges PC78US-6 (with blade) 4001 – 5500 and PC78UU-6 22632 – 23500 with the LPD45 pump. You want the drain plug torque? Page 10-55. 58.8–73.5 Nm (6–7.5 kgfm). Not “tighten until it feels right.”

Hydraulic Pump Port Identification

The OCR excerpt on the first pages is pure gold. It lists every pressure port, drain, and suction line with the corresponding Komatsu labels. P1 and P2 are pump discharge, P3 is gear pump discharge, P4 pilot pump discharge. The diagram shows P1T and P2T – travel deviation adjustment orifices – along with PD2 (pump drain plug) and the PC valve ports. If you have ever wired a pressure transducer to the wrong port and watched the gauge peg, you understand why this matters. The manual includes both with-blade and without-blade configurations, each with separate port layouts.

Torque Specs That Match the Casting

Three torque ranges appear in the pump section. The small fittings like PEN get 7.8–9.8 Nm (0.8–1.0 kgfm). The EPC main pressure pickup port requires 19.6–27.5 Nm (2.0–2.8 kgfm). The big pump drain plug PD2 calls for 58.8–73.5 Nm (6–7.5 kgfm). Those numbers are not suggestions. They come from Komatsu’s own test data. Use a calibrated torque wrench – the manual won’t save your knuckles if you overshoot and crack the housing.

Short paragraph to break rhythm: The LS valve and PC valve cross-sections on page 10-59 are worth the price of the manual alone.

Who Actually Needs This Manual?

DIY owners who buy a used PC78US-6 and want to service the hydraulic pump without pulling the whole machine apart. Shop mechanics who bill by the hour and cannot afford to chase down a mislabeled port. Home garage enthusiasts who trust factory torque values over YouTube comments. This manual does not assume you know which plug is the drain. It shows you – in the same layout a Komatsu field technician would use. If you are swapping the rocker cam, shoe, piston, or servo piston (listed on page 10-58), you need the correct disassembly sequence.

Factory vs Aftermarket: The Real Difference

Aftermarket manuals take the original Komatsu PDF, strip out pages, and compress images until the port labels blur. They omit the serial number range verification. What you hold here is the genuine Technical Manual for LPD45 pump – exactly 123 pages. No reprint house touched it. The document includes the hydraulic pump function description, the EPC valve details, and the PC valve output pressure logic. If you are diagnosing a low-flow condition, the differential between PPLS (LS pump pressure input) and PLS (LS pressure from control valve) is spelled out. That level of detail disappears in photocopied garbage.

Frequently Asked Questions

Does this manual cover the PC78UU-6 as well?

Yes. The same 123-page document covers PC78UU-6 (with blade) serial number 22632 – 23500 and PC78US-6 (with blade) 4001 – 5500. Both use the LPD45 pump. The without-blade configuration is also included – port diagrams differ slightly, and both are in the manual.

What torque values are listed for the pump drain plug?

58.8–73.5 Nm (6–7.5 kgfm). Found on the first page of the hydraulic pump section. Use an inch-pound wrench if you prefer – the conversion is printed.

Where are the hydraulic pump component breakdowns?

Page 10-58 shows the exploded view with shaft, flange, rocker cam, shoe, piston, cylinder block, valve plate, servo piston, and oil seal. Each part is keyed to the same letter labels used in the assembly instructions. No guessing which way the servo piston faces.

Can I use this manual for other Komatsu excavator models?

Not reliably. The port labeling (P1, P2, P3, PPLS, etc.) is specific to the LPD45 pump on the PC78US-6 series. A different model may have different port assignments or torque specs. Buy the correct manual for your machine. That said, if you have a related machine, check the Komatsu PC78UU-6/US-6 Workshop Manual for more coverage or the KOMATSU PC78US-6 PC78UU-6 Shop Manual 2003 for year-specific updates. For other hydraulic calibration procedures, the DEMAG KOMATSU H285 S Hydraulic Calibration manual addresses a different pump family.

Related reference: The Manual Transmission section in the workshop manual may apply if you are servicing the travel motor. Also see Manual Transmission for gear reduction details – though this is a hydrostatic drive, some planetary stages are covered in the transmission documentation.

Access the Factory Manual. Stop relying on a pirated scan that loses half the page every time you zoom in. This is the original 123-page PDF with all port diagrams, torque specs, and structural standards. Your hydraulic pump will thank you – and so will your next paycheck.