Resynchronizing an out-of-sync tower boom or bleeding the oscillating axle lockout cylinders is the job you'll be on within the hour, and the JLG 800A, 800AJ service manual PDF (OEM part 3120740, 452 pages) holds the factory procedure for both aerial work platforms. Electrical schematics and CANbus analyzer diagnostics take up roughly the last quarter of the book, while hydraulic schematics trace the pump, main valve and cylinder circuits you'll be pressure-setting. Chassis and turntable work is the biggest section, about a third of the manual, splitting drive brake, drive motor and swing hub rebuilds by serial number break so the procedure matches your machine. Change the hydraulic return and charge filters after the first 50 hours, then every 6 months or 300 hours; swing bearing bolts torque to 240 ft. lbs. (326 Nm) on both races. UMS calibration faults never happen at a convenient height. The bookmarked, searchable PDF goes wherever the machine is parked.
What's Inside This JLG 800A, 800AJ Manual
| System | Pages | Key Topics |
|---|---|---|
| Introduction - Maintenance Safety Precautions | 3-20 | Hydraulic System Safety, Maintenance |
| Specifications | 21-42 | Operating Specifications (Capacities) |
| General | 43-54 | Machine Preparation, Inspection |
| Chassis & Turntable | 55-212 | Tires & Wheels (Tire Inflation, Tire Damage, Tire Replacement, Wheel Replacement, Wheel Installation) |
| Platform and Rotator Assembly | 213-220 | Platform Support Removal, Platform Sections Replacement, Rotator and Slave Cylinder Removal, Upright Removal |
| Tower Boom Assembly | 221-235 | Tower Boom Assembly Removal, Tower Boom Assembly Installation, Hose Replacement, Limit Switch Adjustment |
| Wear Pads and Rotator Assembly | 236-242 | Wear Pad Replacement, Rotator Disassembly, Rotator Inspection, Rotator Assembly |
| Rotator Assembly (S/N 0300067538 to Present) | 243-252 | Rotator Disassembly, Rotator Inspection, Rotator Assembly, Counterbalance Valve Installation |
| Upright Monitoring System (UMS) | 253-276 | Drive Card Setup, Foot Switch Adjustment, UMS Re-Synchronizing, UMS Troubleshooting, Calibration Faults |
| Hydraulics Theory and Repair | 277-307 | Lubricating O-Rings, Cylinder Theory, Cylinder Checking Procedure, Cylinder Repair, Pressure Setting Procedures |
| Hydraulic Component Maintenance | 308-326 | Main Valve Components, Cylinder Removal and Installation, Hydraulic Pump Coupling Lubrication, Hydraulic Component Start-Up |
| JLG Control System and Electrical Schematics | 327-452 | CANbus Communications, Analyzer Diagnostics, Electrical Multimeter Basics, Electrical Schematics |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| Swing Bearing Outer Race Torque | 240 ft. lbs. (326 Nm) | p. 102 |
| Rotator center bolt torque | 480 ft. lbs. (651 Nm) | p. 215 |
| Hydraulic Return Filter Replacement Interval | Change after first 50 hrs. and every 6 months or 300 hrs. thereafter | p. 31 |
| Hydraulic Charge Filter Replacement Interval | Change after first 50 hrs. and every 6 months or 300 hrs. thereafter | p. 31 |
| Battery voltage | 9.0V - 16.0V | p. 272 |
| Air Filter Replacement Interval | Every 6 months or 300 hours of operation | p. 33 |
| Swing Bearing Inner Race Torque | 240 ft. lbs. (326 Nm) | p. 102 |
| Rotator retaining bolts torque | 50 ft. lbs. (68 Nm) | p. 215 |
| UMS sensor frequency | 100Hz +/- 5Hz | p. 273 |
| UMS sensor duty cycle | 50% +/- 21% | p. 273 |
| Wheel Bolts Torque | 300 ft. lbs. (407 Nm) | p. 25 |
| Support to Rotator Bolts Torque | 50 ft. lbs. (68 Nm) | p. 25 |
JLG 800A, 800AJ Common Problems This Manual Covers
JLG 800A/800AJ upright monitoring system reporting a UMS sensor fault or sensor not calibrated
Verify battery voltage reads 9.0V to 16.0V per page 272, then measure the UMS sensor output on page 273: frequency must read 100Hz +/- 5Hz with a 50% +/- 21% duty cycle. If the analyzer reports the sensor not calibrated, calibrate the sensor using the upright monitoring system calibration procedure on page 256 (pre-ADE machines) or page 260. Re-synchronizing on page 254 corrects physical upright alignment and is a separate job.
Manual Section: Upright Monitoring System (UMS) p. 273Hydraulic system running hot during operation with sluggish actuator response and excessive noise or vibration
Check the hydraulic tank level first; the tank holds approx. 40 gallons (151.4 liters) per page 21. Replace the return filter if it is past its interval: after the first 50 hrs., then every 6 months or 300 hrs. per page 31. Then work through the pump troubleshooting tables on page 320 for sluggish actuator response and a system operating hot.
Manual Section: Hydraulic Component Maintenance p. 320Hydraulic pump showing low output flow and system pressure not reaching the pressure compensator setting
Verify tank level against the approx. 40 gallon capacity on page 21 before condemning the pump. Replace the charge filter if it has gone past 6 months or 300 hrs. (page 31). Then check pressure settings using the Pressure Setting Procedures in Hydraulics Theory and Repair starting on page 305, and recheck for high inlet vacuum.
Manual Section: Hydraulics Theory and Repair p. 305Drive brake slipping, dragging and running hot, or brake will not release at all
On S/N 56875 to 83332 machines with the Mico drive brake (section on page 68), work Table 3-2 Troubleshooting on page 70 for brake slips, brake drags or runs hot, and brake will not release. Back pressure in the actuation line or oil in a dry brake reduces holding torque; check disc stack thickness and release pressure before replacing parts.
Manual Section: Drive Brake Troubleshooting p. 70Drive motor making excessive noise or vibration, running hot, slow to start or will not shift
Start with the drive motor troubleshooting tables on page 84: check oil level in the hydraulic reservoir and oil supply to the motor, since low fluid causes cavitation noise and overheating. Then check for air in the system, output shaft coupling and alignment, the heat exchanger and system relief valves, and work Table 3-5 for won't shift or slow to start.
Manual Section: Drive Motor Troubleshooting p. 84GM engine on LPF fuel system with hard start, cutting out, misses, or rough unstable idle
On GM engines, follow the LPF Fuel System Diagnosis on page 197: check for DTCs in the ECM and the fuel supply before pressure tests, then use Symptom Diagnosis for no start, hard start, cuts out, misses and rough idle. Replace the engine air filter if it has passed 6 months or 300 hours of operation per page 33. Deutz EMR 2 machines, S/N 85331 to present only, use the section on page 170 instead.
Manual Section: GM Engine Fuel System Diagnosis p. 197Frequently Asked Questions
How do I clear DTCs from the ECM on the JLG 800A/800AJ EFI engine?
To clear the trouble codes from the ECM, you must shut off the electrical current running to the ECM. This is done by disconnecting the negative terminal from the battery for a period of approximately 15 minutes. p. 147
What are the torque specifications for the swing bearing bolts on the JLG 800A/800AJ?
The swing bearing bolts should be torqued to 240 ft. lbs. (336 Nm). These bolts must be checked for security after the first 50 hours of operation and every 600 hours thereafter. p. 25
How do I troubleshoot UMS sensor faults?
If the UMS sensor frequency is outside the 100Hz +/- 5Hz range or the duty cycle is outside 50% +/- 21% range, the control system will report a fault. You should inspect the wire harness going to the sensor and UMS module, inspect the sensor mounting, or replace the sensor. p. 273
What are the replacement specifications for the hydraulic oil return filter on the JLG 800A/800AJ?
Page 31 says to change the hydraulic return filter after the first 50 hrs. and every 6 months or 300 hrs. thereafter, or as indicated by the condition indicator. The filter table on page 24 lists the return filter as 10 Microns Absolute. p. 24
What is the torque specification for the wheel bolts on the JLG 800A/800AJ?
The wheel bolts must be torqued to 300 ft. lbs. (407 Nm), with a 150-hour check interval in the torque table on page 25. Page 56 adds that wheel nuts should be torqued after the first 50 hours of operation and after each wheel removal. p. 25
How is this JLG 800A Service Manual delivered?
Immediate download of the complete 452-page searchable Service Manual. Access it on any device, from a laptop at your desk to a phone in the field.
Can I print this JLG 800A manual?
Yes. Print a single page or a chapter for your own shop use, on letter or A4.
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