Description

Komatsu D31EX-21, D31PX-21, D37EX-21, D37PX-21 2007 Workshop Manual

If you’re trying to rebuild a hydrostatic transmission or set valve lash on the SAA4D102E-2 engine without the factory numbers, you’re already in trouble. I’ve seen guys torch a good engine because they guessed on the torque sequence. Komatsu D31EX-21, D31PX-21, D37EX-21, D37PX-21 2007 Workshop Manual puts the OEM specs in your hands – 465 pages of them. This isn’t some aftermarket summary that leaves out the critical stuff. It’s the same book the dealer techs use, pulled straight from the factory.

Every time I see a DIY guy trying to cobble together information from a forum, I cringe. You spend hours chasing a problem that a five-minute look at the right page would have solved. That’s what this manual is for. It’s not a novelty; it’s a tool. Same as a torque wrench. You wouldn’t tighten a head bolt with a breaker bar and guess the foot-pounds, so why guess on fuel injection timing or HST charge pressure?

Engine and Fuel Systems: Factory Specs You Can Trust

Section 01 gives you the full spec sheet for the D31 and D37 series, including the table of Fuel, coolant, and lubricants. You need to know the exact oil viscosity for the HST pump? It’s in there. The Cooling system section (part of 10) walks you through the radiator, fan belt replacement procedure, and even the air conditioner compressor belt tension. I’ve watched mechanics ruin a water pump because they didn’t check the belt tension sequence in the manual. Don’t be that guy.

The Engine control chapter covers everything from the stop solenoid linkage adjustment to the decelerator pedal linkage. You get the standard value table for engine testing – compression pressure, blow-by pressure, intake boost pressure. These aren’t suggested numbers; they’re Komatsu’s acceptance criteria. If you’re off by more than a few psi, you’ve got a problem that needs fixing before you put the machine back to work.

Adjust Valve Clearance the Right Way

Page 20-1 kicks off the testing and adjusting section. One of the first procedures is adjusting Valve clearance. I’ve seen shops skip this because they think it’s a waste of time on a diesel. On the SAA4D102E-2, it’s critical. The manual gives you the cold clearance spec and the exact steps – no shortcuts. You also get the fuel injection timing test and adjustment. If you’ve ever had a Komatsu that wouldn’t start when cold or smoked white, you know the injection timing is the first place to look. The manual includes the procedure for using the timing tool and measuring the pre-stroke.

Don’t even think about using a generic diesel manual for this. The aftermarket stuff won’t have the specific solenoid valve output pressures or the HST oil pressure specs. For example, the HST brake quick return circuit and the charge safety valve adjustments are unique to this model line. You’ll find those in section 10 under the steering and Brake control chapters. I’ve had to redo work on a D37PX-21 because a tech used a universal transmission pressure spec – cost the shop a weekend and a set of clutches.

465 Pages of OEM Specifications

Thickness matters. This manual is a heavy binder because it covers every system – power train, HST pump, final drive, track frame, idler, sprocket, track shoe, work equipment, cab related, monitor system, sensors. The electrical troubleshooting section alone is a small book. It has connector arrangement diagrams, connector pin connection tables, and E-mode troubleshooting for everything from the starting motor to the windshield wiper. If you’ve ever had a parking brake solenoid that won’t release, you can go straight to E-8 and find the circuit diagram and test points.

One thing I appreciate is the tools list for testing and adjusting. They tell you exactly what you need – like a tachometer for engine speed measurement, or a pressure gauge for HST oil pressure. None of that ‘you’ll need a suitable tool’ garbage. It’s specific: part numbers, ranges, and adapters. If you’re a home garage guy, you can cross-reference the tools with aftermarket equivalents, but at least you know what the factory expects.

Brake and Steering Control Systems

Section 10 includes the steering, directional PPC valve, automatic gearshifting valve, inching valve, and the parking brake control system. If you’re working on a D31PX-21 that wanders or won’t steer straight, the travel deviation test and adjustment procedure is in the testing section. The manual also explains the safety mechanism when starting the engine – a lot of operators don’t realize you have to have the gearshift in neutral and the parking brake applied. The wiring diagrams and solenoid tests are there so you can verify the interlock without shooting parts at it.

I’ve seen a lot of guys try to rebuild the HST motor without the factory clearance specs. The manual gives you the internal clearances for the swashplate and the cylinder block. Without those numbers, you’re gambling on whether the motor will hold pressure. That’s not a risk I’d take on a jobsite.

Does This Manual Cover the Cooling System?

Yes. Section 10 has a dedicated cooling system subsection covering the radiator, fan, and the air conditioning compressor belt adjustment. The standard value table for chassis includes cooling system pressures and temperature ranges. If you’re troubleshooting an overheating D37EX-21, you can find the coolant flow rate and the charge pump specs. The manual also includes the bleeding procedure for air from the fuel circuit – a step that’s often forgotten after a filter change. Bleeding air from hydraulic cylinders is covered too, which is essential after replacing a work equipment cylinder.

I’ll tell you straight: aftermarket manuals tend to lump cooling systems together across multiple models. That’s useless when the tensioner pulley design or the belt routing changes between the D31 and the D37. This OEM manual spells out the exact fan belt replacement sequence and the tension measurement in inches of deflection. No guesswork.

If you want to avoid the headaches that come from using third-party data, pick up this manual. It’s the real thing – 2007 publication, 465 pages, direct from Komatsu. Pair it with the Komatsu WA65-5 WA70-5 WA80-5 2005 Workshop Manual if you also work on wheel loaders, or the Komatsu WH609-1E0 WH613-1E0 WH713-1E0 WH714H-1E0 WH716-1E0 Workshop Manual for the telehandler line. For more detailed specs on the 102-2 engine family, see the Komatsu PW95R-2 Workshop Manual – 520 Pages of Factory Specs.

Working on the HST system in these dozers is different from a Manual Transmission – the pressures and controls are hydraulic, not mechanical. However, if you need to understand the basic principles of gear meshing, a Manual Transmission tutorial can give you context, but don’t use it for your Komatsu.

Access the Factory Manual and keep it near the toolbox. You’ll use it every time you touch one of these machines.

Can I use this manual for the D39EX model?

No. This is specifically for D31EX-21, D31PX-21, D37EX-21, and D37PX-21.

Does the manual include wiring diagrams and electrical troubleshooting?

Yes. Section 20 includes a full electrical system troubleshooting section with connector arrangement diagrams, pin numbers, and failure mode tables. For example, the E-mode troubleshooting covers starting motor issues, parking brake solenoid, travel speed control, and more. The manual also includes standard value tables for the electrical system. This is essential for diagnosing sensor and controller problems on these Komatsu dozers.