Boom, cab, axles, transmission, engine, hydraulics and electrical: this 566-page JLG 1255 service manual PDF (OEM ID 31211033) walks each system end to end across six JLG telehandlers, 642 through 1255. Full hydraulic schematics trace flow from the implement pump through the control valves to each cylinder, and separate harness schematics for the 642 to 1043 group and the 1055/1255 keep your wiring traces on the right frame. More than a third of the book is fault code listings (machine codes, engine SPN and aftertreatment faults), so a code on your display leads straight to its cause. Set total wear pad gap to 0.019 to 0.059 in (0.5 to 1.5 mm) against the next boom section, then torque the reservoir drain plug to 22 to 29 lb-ft (30 to 40 Nm). A made-up torque figure on a loaded boom hurts people. Bookmarked and text-searchable, the PDF is yours to keep for the life of that machine.
What's Inside This JLG 642–1255 Telehandlers Manual
| System | Pages | Key Topics |
|---|---|---|
| Safety Practices | 9-12 | Introduction, Disclaimer, Operation & Safety Manual, Do Not Operate Tags, Safety Information (Safety Alert System and Signal Words) |
| General Information and Specifications | 13-98 | Replacement Parts and Warranty Information |
| Boom | 99-144 | Boom System Component Terminology, Boom System, Boom Removal/Installation, Boom Assembly Maintenance - 642, 742, 943, 1043, Third Boom Section Removal/Installation Only - 642 |
| Cab | 145-158 | Operator Cab Component Terminology, Operator Cab, Cab Components, Cab Removal, Cab Installation |
| Axles, Drive Shafts, Wheels and Tires | 159-174 | Axle, Drive Shaft and Wheel Component Terminology, Axle Serial Number, Axle Specifications and Maintenance Information, Axle Replacement, Brake Inspection |
| Transmission | 175-182 | Transmission Assembly Component Terminology, Transmission Serial Number, Specifications and Maintenance Information, Transmission Replacement, Transmission Fluid/Filter Replacement |
| Engine | 183-210 | Introduction, Engine Serial Number, Specifications and Maintenance Information, Engine Cooling System, Engine Electrical System, Fuel System, Engine Exhaust System |
| Hydraulic System | 211-270 | Hydraulic Component Terminology, Safety Information, Specifications, Hydraulic Pressure Diagnosis, Hydraulic Circuits, Hydraulic Schematic, Hydraulic Reservoir, Implement Pump |
| Electrical System Overview and Power Distribution | 271-286 | Electrical Component Terminology, Power Distribution Boards, Cab Power Distribution, Frame Power Distribution, Engine Harness Fuses and Relays |
| Electrical System Schematics (642, 742, 943, 1043) | 287-293 | Cab Harness Schematics, Engine Harness Schematics, ULS Engine Harness, Option Harnesses |
| Electrical System Schematics (1055, 1255) | 294-308 | ULS Engine Harness, LS Engine Harness, Option Harnesses, Cab Harness Schematics |
| Multifunction Display and Setup | 309-348 | Multifunction Display, Setup and Maintenance, Access Levels, Programming, Capacity Charts |
| Machine Fault Codes (00x - 46x) | 349-495 | Help Comment, Power Up, Platform Controls, Cabin Controls, Output Drivers, Transmission and Drive System |
| Engine Diagnostics and Fault Codes (SPN) | 496-566 | Engine Diagnostic, SPN Fault Codes, Aftertreatment System, Engine Sensors, Communication Faults |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| All Models | ||
| Hydraulic oil reservoir drain plug torque | 22 - 29 lb-ft (30 - 40 Nm) | p. 246 |
| Acceptable total gap between the side/top wear pad(s) and the next boom section | 0.019 - 0.059 in (0,5 - 1,5 mm) | p. 132 |
| Bolt length tolerance | ± 0.004 in (±1,0 mm) | p. 133 |
| Engine coolant temperature sensor torque | 12.5 - 17 lb-ft (17 - 23 Nm) | p. 362 |
| Boom angle sensor rod length | 8.26 - 8.34 in (210 - 212 mm) | p. 363 |
| Wheel lug nut torque | 350-400 lb-ft (475-542 Nm) | p. 21 |
| Engine Crankcase Oil Capacity (with filter change) | 14 quarts (13,2 liters) | p. 25 |
| Fuel Tank Capacity | 38.3 gallons (145 liters) | p. 25 |
| 642 | ||
| Hydraulic System Capacity (642, No Outriggers) | 40.2 gallons (152 liters) | p. 25 |
| Hydraulic System Capacity (642, With Outriggers) | 41.7 gallons (158 liters) | p. 25 |
| 943 | ||
| Hydraulic System Capacity (943) | 46.5 gallons (177,0 liters) | p. 26 |
| 1043 | ||
| Hydraulic System Capacity (1043) | 48.6 gallons (184,0 liters) | p. 26 |
JLG 642–1255 Telehandlers Common Problems This Manual Covers
JLG 642 through 1255 telehandler boom shifting side to side during extension and retraction
Measure the total gap between the side and top wear pads and the next boom section. Page 132 sets the acceptable range at 0.019 to 0.059 in (0.5 to 1.5 mm). Replace any pad that falls outside that window, then run the boom through full extension and retraction and recheck for shifting.
Manual Section: Boom Troubleshooting p. 132Boom extension and retraction jerky or uneven with visible wear on the extend and retract chains
Inspect the extend and retract chains for wear along their full length before you make any adjustment. Torque the chain lock and jam nuts to 85 to 92 lb-ft (115 to 125 Nm) as specified on page 112. Then cycle the boom several times and confirm it travels smoothly in both directions.
Manual Section: Boom Troubleshooting p. 112Boom angle sensor machine fault code active on the multifunction display after sensor service
Check the active code in the Machine Fault Codes section and follow its check sequence before replacing parts. Measure the boom angle sensor rod length against 8.26 to 8.34 in (210 to 212 mm), listed on page 363. Adjust the rod if it falls outside that range, then clear the code and retest.
Manual Section: Machine Fault Codes (00x - 46x) p. 363Engine coolant temperature sensor fault code returning after the sensor was replaced in the engine block
Check the code in the fault code section first so you know the sensor is the real cause. Thread the engine coolant temperature sensor into the engine block by hand, then torque it to 12.5 to 17 lb-ft (17 to 23 Nm) per page 362. Clear the code and run the engine to confirm it stays clear.
Manual Section: Machine Fault Codes (00x - 46x) p. 362Axle overheating with oil leaks at the axle and leaking steering cylinders
Inspect the axle and steering cylinders to find the actual leak source, then work through the Axle Assembly and Drive Shaft Troubleshooting checks for overheating, noise, vibration and steering effort. Verify brake engagement during the same check. The axle specifications and maintenance information begin in the axles section on page 159.
Manual Section: Axle Assembly and Drive Shaft Troubleshooting p. 159Main relief, steering or pilot hydraulic pressure reading out of range during pressure checks
Test main relief, steering, auxiliary and pilot pressures using the Hydraulic Pressure Diagnosis checks in the hydraulic system section starting on page 211. Record each reading, adjust any circuit outside its listed setting, and retest after each adjustment. Use the Hydraulic Schematic to trace which circuit is causing the problem.
Manual Section: Hydraulic Pressure Diagnosis p. 211Frequently Asked Questions
What is the torque specification for the wheel lug nuts on the JLG telehandler?
The wheel lug nut torque for all models is 350-400 lb-ft (475-542 Nm). p. 21
Where can I find the fault code list for my JLG telehandler?
The machine fault codes are listed in Section 9.18, starting on page 410. You can find specific fault codes, their descriptions, and latch conditions in the tables provided in that section. p. 410
What are the replacement specifications for boom wear pads on the JLG telehandler?
The acceptable total gap between the side/top wear pad(s) and the next boom section is 0.019 - 0.059 in (0,5 - 1,5 mm). If the gap exceeds this, you must shim each wear pad to within the measurement. p. 132
What is the engine oil capacity for the 642 and 742 models?
The engine crankcase oil capacity with a filter change for the 642 and 742 models is 14 quarts (13,2 liters). p. 25
What is the correct procedure for bleeding the service brake master cylinder?
To bleed the master cylinder, open the master cylinder valve bleeder (19) while an assistant slowly depresses the brake pedal. Close the bleeder when air bubbles no longer appear in the oil, then release the pedal to allow the reservoir to refill. p. 255
Is this JLG 642 manual a PDF I download?
All 566 pages arrive as one searchable PDF at checkout. Read it at the desk, then take the phone out to the machine.
Is this JLG 642 manual print-friendly?
Yes. Print a single page or a chapter for your own shop use, on letter or A4.
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