Part of the Hyundai Repair Manuals.
All 635 pages of this Hyundai HL780-3A Service Manual PDF cover one machine family: your wheel loader, from torque converter to bucket pins. You get full electrical circuit diagrams with connector pinouts and component locations, hydraulic schematics tracing the main pump and control valve circuits, and fault code tables for the electro-hydraulic shift control. Inside: step-by-step disassembly and assembly for the multi-disk clutch packs, differential carrier, and steering system, plus rolling resistance adjustment and contact pattern inspection for the axles. Set the main relief valve at 210 kgf/cm2, and torque the rubber engine mounting nuts to 100 plus or minus 15.0 kgf-m before startup. No more chasing wiring faults with a multimeter and a prayer. Bookmarked chapters, text you can search by spec or fault code, and it opens on any device you carry into the shop.
What's Inside This Hyundai HL780-3A Manual
| System | Pages | Key Topics |
|---|---|---|
| General | 11-35 | Safety Hints, Specifications, Operational Checkout Record Sheet |
| Engine | 36-54 | Structure and Function, Engine Fault Code Information |
| Power Train System Overview | 55-60 | Component Overview, Torque Converter, Transmission Layout |
| Transmission Operation | 61-73 | Installation View, Forward/Reverse Gear Operation, Electro-Hydraulic Shift Control, Transmission Error Display, Aeb Mode |
| Operating Modes and Fault Codes | 74-125 | Operating Mode Definitions, Fault Code Tables, Differential/Axle Troubleshooting, Drive Line Troubleshooting |
| Tests and Adjustments | 126-152 | Clutch Cut-Off Pressure Switch Test, Transmission Measuring Points, Retarder Disassembly/Assembly |
| Transmission Disassembly and Assembly | 153-261 | Transmission Disassembly, Multi-Disk Clutch Disassembly/Assembly, Input Shaft Assembly, Speed Sensor Installation |
| Axle and Differential Maintenance | 262-338 | Final Drive Disassembly, Differential Carrier Disassembly, Differential Assembly, Rolling Resistance Adjustment, Contact Pattern Inspection |
| Brake System | 339-371 | Structure and Function, Operational Checks and Troubleshooting, Tests and Adjustments |
| Steering System | 372-478 | Structure and Function, Operational Checks and Troubleshooting, Tests and Adjustments, Disassembly and Assembly |
| Work Equipment | 479-558 | Hydraulic System Outline, Hydraulic Circuit, Main Pump Operation, Remote Control Valve, Main Control Valve |
| Electrical System | 559-635 | Component Location, Electrical Circuit, Monitoring System, Electrical Component Specification, Connectors, Troubleshooting |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| Engine mounting bolt, nut(Rubber, 4EA) | 100 ± 15.0 kgf·m | p. 29 |
| Engine mounling bolt(Fly wheel housing, 8EA) | 19.4 ± 3.0 kgf·m | p. 29 |
| Main pump maximum operating pressure | 210 kgf/cm² | p. 27 |
| Brake pump maximum operating pressure | 150 kgf/cm² | p. 27 |
| Main relief valve pressure | 210 kgf/cm² | p. 27 |
| Overload relief valve pressure(Boom) | 250 kgf/cm² | p. 27 |
| Steering pump maximum operating pressure | 210 kgf/cm² | p. 27 |
| Nominal value/Bearing rolling moment | 1.4~2.0kgf m | p. 269 |
| Slotted nut torque limit | 204~224kgf m | p. 269 |
| Maximum steering pressure | 21 MPa | p. 376 |
| Bypass valve set pressure | 1.36kg/cm2 (19.3psi) | p. 510 |
| Proximity switch clearance | 3±1mm | p. 525 |
Hyundai HL780-3A Common Problems This Manual Covers
Hyundai HL780-3A wheel loader boom will not lift, bucket won't curl, hydraulics quit responding under load
Check the hydraulic tank level first; check it against the capacity in the General specifications. Test main relief pressure at the pump and compare against the 210 kgf/cm2 spec on page 27. If pressure is low or erratic, pull the suction strainer and filter elements; contaminated oil sticks the main control valve spools. Flush the system and refill with clean oil.
Manual Section: Work Equipment p. 479Hydraulic pump whines and growls at idle, boom raises slowly, pressure gauge needle bounces
Inspect for aeration first: tighten every suction line fitting and top off the hydraulic tank to the level in the General specifications. Verify pump output against the main pump rating in the General specifications. Replace the filter element; it is due every 250 operating hours, and at 50 hours on a fresh fill (page 538). Bleed the air out and retest.
Manual Section: Work Equipment p. 479Steering wheel turns hard in both directions, articulation barely moves at full throttle
Check steering pressure at the test port; maximum steering pressure is 21 MPa (page 376). A low reading points to the steering pump or a stuck priority valve spool. Measure pilot pressure at the flow amplifier and compare it against the steering tests and adjustments section. Clean or replace any spool that drags in its bore.
Manual Section: Steering System p. 376Transmission drives in one direction only, or machine will not move in any gear
Check transmission oil level at the idle speed the manual specifies before touching anything else. Low charge pressure from the filling pump starves the clutch packs, so replace a restricted transmission filter if the monitor flags a filter fault once the oil is warm. Run the pressure checks at the transmission measuring points, starting on page 126.
Manual Section: Transmission Troubleshooting p. 126All four wheels growl and rumble during travel, noise speeds up with ground speed
Jack each axle and check wheel-side tapered roller bearing preload; rolling moment should measure 1.4 to 2.0 kgf·m (page 269), with the slotted nut torqued to 204 to 224 kgf·m. Inspect the sun gear, planetary gears, and ring gear for spalling during final drive teardown, covered starting on page 262. Replace bearings as a set, never singly.
Manual Section: Axle and Differential Maintenance p. 269Frequently Asked Questions
What are the torque specifications for hydraulic fittings on the machine?
The torque specifications for hydraulic fittings depend on the thread size. For example, a 1/4" fitting requires 4 kgf·m (28.9 lbf·ft), a 3/8" fitting requires 5 kgf·m (36.2 lbf·ft), and a 1" fitting requires 15 kgf·m (109 lbf·ft). p. 30
What are the replacement specifications for the hydraulic oil filter element?
The hydraulic oil filter element in the filter case of the hydraulic oil tank should be replaced every 250 operating hours. For the first replacement, it should be done at 50 hours. p. 538
What is the engine oil capacity for the Cummins QSM 11-C engine?
The engine oil capacity for the Cummins QSM 11-C engine is 38 liters (10 U.S. gallons). p. 26
What is the correct procedure for bleeding the hydraulic brake system?
Bleeding the brake system requires two people. Push and hold the brake pedal down until the procedure is complete, and open the bleed screw on the differential and axle assembly until hydraulic oil flows free of air. The full bleeding procedure is in the Brake System section. p. 371
What is the rated pressure for the clutch cut-off pressure switch?
The rated pressure for the clutch cut-off pressure switch is 25 kgf/cm². p. 126
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