Description

Komatsu PC138US-8, PC138USLC-8 Workshop Manual

You are staring at a PC138US-8 that drifts down in the right boom circuit. The aftermarket PDF you bought says 1800 psi for the LS pressure. Wrong. The machine throws a code you’ve never seen. You need the real spec—the one Komatsu engineers wrote when they bolted that machine together. That is what sits inside this factory Komatsu PC138US-8, PC138USLC-8 Workshop Manual. 946 pages of OEM data, no guesses, no third-party rewrites.

Testing and Adjusting Procedures: Engine and Hydraulics

The manual devotes an entire section—Testing and Adjusting, Part 1, 2, and 3—to procedures that keep you from chasing ghosts. Need to set the valve clearance on the SAA4D95LE-5 engine? The steps are there, with the tool list and the correct feeler gauge sizes. Testing the pump PC control circuit pressure? The manual gives you the port locations, the required 50 MPa gauge, and the offset adjustment sequence. Every test in the hydraulics section (swing motor, travel motor, CLSS logic) is written for a technician with a wrench in hand, not a writer looking to fill space. For the travel deviation test, the manual specifies the straight travel distance, the load conditions, and the acceptable drift number. That kind of detail saves you a comeback.

Standard Value Tables: What You Need

Section 20 – Standard Value Table contains two separate tables: one for engine-related parts, one for chassis-related parts. If you are rebuilding the swing circle, you look up the bearing clearance standard there. The table lists the allowable limits, not just the new-part specs. Same for the track adjuster seals, the final drive backlash, the swing reduction gear tooth contact pattern. These tables are cross-referenced from the Structure, Function and Maintenance Standard section, so the numbers match the assembly drawings. No guessing whether 0.003 inch clearance is safe. The factory says it is—or it isn’t.

Troubleshooting by Failure Code

Section 40 – Troubleshooting breaks down every failure code organized into four parts. The failure code table at the start (page 3 of the section) lists each E-code, the fault location, and the applicable machine monitor procedure. The troubleshooting flowcharts then walk you through voltage checks, resistance measurements, and hydraulic pressure tests. For electrical system E-mode troubleshooting, the manual includes wiring diagrams with connector pin numbers. That is the difference between swapping parts and finding the chafed wire behind the cab. If you are dealing with a KOMTRAX communication error, the dedicated subsection under Electrical System tells you the signal path and the controller diagnostic steps.

Hydraulic System Part 1 and 2: CLSS and PC Control

Three separate hydraulic sections cover everything from the layout drawing to the pilot pressure control. Part 1 maps the hydraulic equipment layout and dives into the pump control (PC) valve and LS control. Part 2 explains the CLSS (Closed-Loop Load Sensing) system—the valve functions, the standby pressure, and the signal relief setting. If you have never repaired a Komatsu CLSS pump before, the section on “Functions and Operation by Valve” shows you the spool cutaway and the pressure port identification. The manual also covers the PPC valve, the holding valve, and the multi-control valve. Every component torque value is listed in the standard tightening torque table in the foreword (page 5 of the index section). That is where you find the correct ft-lb for the pump mounting bolts—not a generic chart from a 1980 pickup manual.

Source Authenticity: Why OEM Factory Specs Matter

I have seen a $4,000 hydraulic pump destroyed by a technician who used an aftermarket torque spec that was 20 N·m too low. The Komatsu factory manual—the same one Komatsu dealers use—has the exact figures for every bolt, every thread locker specification, and every shim selection. The standard tightening torque table at the front of the manual is specific to this machine series. The wiring codes follow the Komatsu JIS standard, not a generic color-coding. If you want to keep your PC138US-8 running at production rates, you use the document Komatsu wrote for it, not a scanned copy of a third-party translation. For related machines, check the Komatsu PC138US-8 PC138USLC-8 Workshop Manual for the same format, or the Komatsu PC138US-8 / PC138USLC-8 Operation & Maintenance Manual for daily service intervals. If you work on other Komatsu equipment, the Komatsu WA65-5 WA70-5 WA80-5 2005 Workshop Manual follows the same chapter structure.

For a broader understanding of hydraulic transmission principles—though this excavator uses a dedicated hydraulic drive—you can reference Manual Transmission on Wikipedia for the basics of gear reduction, and Manual Transmission for power flow diagrams. But for this machine’s specific hydrostatic travel motor, stick with the factory manual’s exploded views.

Does This Manual Cover the PC138US-8 with Serial Numbers After 20001?

Yes. The manual lists serial numbers PC138US-20001 and up, and PC138USLC-20001 and up.

How Do I Release Residual Pressure from the Hydraulic Circuit Before Servicing?

Go to Section 30 – Testing and Adjusting, Part 1. The procedure titled “Releasing residual pressure from hydraulic circuit” specifies you must start the engine, lower the work equipment to the ground, then shut the engine off. Move the control levers in all directions to relieve any trapped pressure in the pilot circuit. After that, slowly loosen the hydraulic tank filler cap to release tank pressure. The manual also warns that you must wait at least 30 seconds after engine shutoff before opening any hydraulic fittings—this allows the accumulator pressure to drop below 50 psi. Failure to do this can inject hot oil into your face. The manual shows the exact location of the hydraulic tank air breather and the accumulator release valve. Every step is listed with safety warnings, so you don’t learn the hard way.

That level of detail is why I keep a copy of this 946-page Workshop Manual on the tool box shelf, not a tablet with some subscription service. You want the real Komatsu data? Access the Factory Manual from the link below and get the same specs the dealer’s techs use.