Cat 785C, 789C Off-Highway Trucks Service Training Guide (SESV1706)

These 785C and 789C trucks live in rough spots—big mines, heavy construction, hauling rock all day on torn‑up haul roads. This service training guide isn’t a quick “how-to,” it’s meant to teach you how the systems think, so you can trace a fault instead of just throwing parts. You’ll walk through hydraulic, electrical, and powertrain theory, then see how failures usually show up in the real world. Say a truck keeps losing pull on a grade: with this manual you’d know how to isolate whether it’s fuel, transmission control, or a slipping brake, then test in a logical order instead of guessing.

Applications & Use Cases

• Walk new techs through system theory so they can trace circuits, route harnesses correctly, and avoid rookie wiring mistakes.
• Use the step-by-step exercises to check pressures, verify sensor signals, and compare results to what you’d typically expect.
• Practice safe lockout, support, and bleed-down procedures in the classroom before anyone crawls under a live truck.
• Run through fault scenarios to inspect components, align linkages, and test switches so your crew builds a standard way to diagnose.
• Review it before a shutdown so the team can isolate likely failures faster and cut down on random parts changing.

FAQ

Q: Is this a searchable PDF I can keep on a laptop in the shop?

A: It’s usually supplied as a standard PDF, so you can search terms, jump sections, and keep it open while you work.

Q: Can I print just a few sections to take up on the bench or into the pit?

A: Yes, most folks print the procedures or schematics they need, slip them in plastic sleeves, and don’t worry if they get dirty.

Safety Note

Always verify the truck is fully locked out, blocked, and any stored energy bled off before you inspect or test anything on it.

Cat 785C, 789C Off-Highway Trucks Index:

INTRODUCTION …………………………………………………………………………………………………………7
WALK AROUND INSPECTION…………………………………………………………………………………..11
OPERATOR’S STATION………………………………………………………………………………………………45
ENGINE……………………………………………………………………………………………………………………..65
Engine Electronic Control System ……………………………………………………………………………66
Cooling System………………………………………………………………………………………………………88
Lubrication System …………………………………………………………………………………………………97
Fuel System………………………………………………………………………………………………………….101
Air Induction and Exhaust System ………………………………………………………………………….106
POWER TRAIN ………………………………………………………………………………………………………..111
Torque Converter ………………………………………………………………………………………………….112
Torque Converter Hydraulic System………………………………………………………………………..115
Transmission and Transfer Gears…………………………………………………………………………….125
Transmission Hydraulic System ……………………………………………………………………………..128
Differential …………………………………………………………………………………………………………..138
Final Drives………………………………………………………………………………………………………….144
Transmission/Chassis Electronic Control System ……………………………………………………..145
STEERING SYSTEM ………………………………………………………………………………………………..155
HOIST SYSTEM……………………………………………………………………………………………………….188
AIR SYSTEM AND BRAKES ……………………………………………………………………………………208
Air Charging System……………………………………………………………………………………………..210
Brake Systems………………………………………………………………………………………………………217
BRAKE ELECTRONIC CONTROL SYSTEM……………………………………………………………..237
Automatic Retarder Control (ARC)…………………………………………………………………………240
Traction Control System (TCS) ………………………………………………………………………………245
OPTIONAL EQUIPMENT………………………………………………………………………………………….253
FlexxaireTM Fan …………………………………………………………………………………………………….253
CONCLUSION………………………………………………………………………………………………………….256
SLIDE LIST………………………………………………………………………………………………………………257
SERVICEMAN’S HANDOUTS…………………………………………………………………………………..260

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