A transaxle that starts slipping under load, or an ignition that drops the truck dead mid-aisle, is what the 895-page Clark GCS service manual PDF (OEM number SM520) was written to settle. Covering the GCS, GCX, DCS, GPX, GPS and DPS series, this factory book runs from General Information through the Uprights section. Electrical system wiring diagrams trace ignition and charging circuits back to the battery, while the hydraulic chapter walks the sump fluid and filter change through to a full main pump overhaul. Main relief pressure is tuned to capacity, 2300-2400 psi on GC(P)S(X) 17-20 trucks. Set idle at 650 rpm nominal on both the 4G54 and TM(D)27 engines, with 600 to 700 rpm as the acceptable band, and check that Group 31 battery for its rated 625 amps at 0F. A guessed brake pressure puts a loaded truck somewhere it should not be. Bookmarked, searchable, yours once you buy it.
What's Inside This Clark GCS, GPS Series Manual
| System | Pages | Key Topics |
|---|---|---|
| General Information | 5-14 | Safe Maintenance Practices, Product Identification |
| Specifications | 15-36 | Product Specification Changes, Service Specifications |
| Planned Maintenance | 37-63 | PM Schedules, Planned Maintenance Procedures |
| Engine | 64-188 | Engine Troubleshooting, Engine Tune-Up, Engine Adjustments |
| Fuel System | 189-286 | Fuel Systems Maintenance, LPG Fuel System |
| Electrical System | 287-400 | Electrical System Wiring, Ignition System Maintenance |
| Transaxle | 401-646 | Transaxle Maintenance, Transaxle Overhaul General Procedures |
| Brakes and Inching System | 647-685 | Service Brake and Inching Systems, Brake and Inching System Type 1 |
| Steering System | 686-766 | Steering Column Removal and Installation, Steer Axles |
| Hydraulic System | 767-812 | Hydraulic Sump Fluid and Filter Change, Main Hydraulic Pump Overhaul |
| Wheels and Tires | 813-833 | Cushion Tire and Wheel Maintenance, Pneumatic Tire and Wheel Maintenance |
| Counterweight and Chassis | 834-850 | Counterweight Maintenance, Chassis Components |
| Uprights | 851-872 | Upright Maintenance, High Visibility Standard Upright |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| G54, D176GA | ||
| Battery 1 Cold Crank Current | 420 amps @ 0°F | p. 18 |
| TM27 | ||
| Battery 2 Cold Crank Current | 320 amps @ 0°F | p. 18 |
| 4G54 Engine | ||
| Idle Speed Setting | 650 rpm, nominal (Range: 600-700 rpm) | p. 136 |
| All Models | ||
| 4G54 Engine Idle Speed | 650 rpm (600-700 rpm) | p. 83 |
| TM(D)27 Engine Idle Speed | 650 rpm (600-700 rpm) | p. 83 |
| Steering cylinder thru fastener nut torque | 40-45 Nm (30-33 lbf.ft) | p. 766 |
| 4G54 | ||
| Engine Oil Capacity (4G54) | 4.5L | p. 20 |
| Cooling System Capacity (4G54) | 8.5L | p. 20 |
| TM27/TMD27 | ||
| Engine Oil Capacity (TM27/TMD27) | 6.6L | p. 21 |
| Cooling System Capacity (TM27/TMD27) | 8.5L | p. 21 |
| D176GA | ||
| Engine Oil Capacity (D176GA) | 4.7L | p. 22 |
| Cooling System Capacity (D176GA) | 8.5L | p. 22 |
Clark GCS, GPS Series Common Problems This Manual Covers
Clark GCS 25 forklift cranks slowly or won't turn over on cold mornings
Load test the battery before condemning the starter. On 4G54 and D176GA trucks the battery is a 12 volt BCI Group 73 rated 420 amps at 0 degrees F, listed on page 18. Clean both posts, then work the starting system troubleshooting steps and check starter current draw.
Manual Section: Electrical System p. 18Lift and tilt go weak, stall halfway up, or stop moving under load
Check sump fluid level first, then gauge the main relief pressure at the pump port. On GC(P)S(X) 17-20 trucks the setting on page 27 is 2300-2400 psi. If pressure is low or spools hang up, pull the main valve and work through the hydraulic troubleshooting chart.
Manual Section: Hydraulic System p. 27Engine runs rough at idle, surges, or dies when the operator lets off the pedal
Warm the engine to operating temperature, then measure idle speed with a tach. Set it to 650 rpm nominal, within a 600 to 700 rpm range as specified on page 83. Inspect vacuum lines and the LPG regulator for leaks, then verify ignition timing before touching the throttle stop screw.
Manual Section: Engine p. 83Truck loses power climbing ramps and transmission oil gets hot after a long shift
Check clutch pressure and converter out pressure at the test ports with the engine at operating temperature. Compare readings against the transmission troubleshooting chart. Verify the cooling system holds its full 8.5L charge, listed on page 20 for 4G54 trucks, and clean debris out of the radiator and oil cooler fins.
Manual Section: Transaxle p. 20Steering wanders, feels loose, or the truck pulls hard to one side
Inspect the steer cylinder rod ends and tie rod sockets for play with the wheels off the ground. Retorque the steering cylinder thru fastener nuts to 40-45 Nm (30-33 lbf.ft) per page 766. Then set steer tire pressure to 115 psi and drive tires to 140 psi on GPS(X) 20-30 units.
Manual Section: Steering System p. 766Inching pedal has no freeplay and the truck creeps forward with the brake applied
Measure pedal freeplay at the pad and adjust the inching rod until the slave cylinder fully returns. Bleed the system and check for leaks at the master and slave cylinder seals. If the clutch only partially disengages, work the inching troubleshooting guide and inspect the slave cylinder bore for sticking.
Manual Section: Brakes and Inching System p. 647Frequently Asked Questions
What is the engine oil capacity for the Mitsubishi 4G54 2.6L engine in a Clark GCS forklift?
The engine oil capacity for the Mitsubishi 4G54 [2.6L] engine, including the filter, is 4.8 quarts [4.5L]. p. 20
What is the correct valve clearance for the Continental TM27 2.7L engine in a Clark GCS forklift?
For the Continental TM27 [2.7L] engine, the intake valve clearance is 0.014 inches [0,36 mm] and the exhaust valve clearance is 0.018 inches [0,46 mm], measured warm. p. 21
What is the drive wheel lug nut torque spec on the Clark GCS/GCX/DCS/GPS/GPX/DPS forklift chassis?
The tightening torque for the drive wheel lug nuts/bolts is 470-530 lbf.ft [637-718 Nm]. p. 32
What is the recommended coolant mixture for the cooling system?
The cooling system should be filled with a mixture of 50% water and 50% low-silicate ethylene glycol permanent-type antifreeze containing rust and corrosion inhibitors. p. 18
What is the correct torque spec for the main hydraulic pump mounting bolts on my Clark GCS forklift?
The main hydraulic pump mounting bolts should be tightened to 53-59 lbf.ft [72-80 Nm]. p. 32
Is this Clark GCS manual a download or a disc?
This is a 895-page searchable PDF ready for immediate download. Works on any device, so pull it up on your phone while you're under the hood. No shipping, no waiting.
Am I free to print this Clark GCS Service Manual?
Yes, print as many copies as you want, and there are no restrictions. Many mechanics print the section they need and bring it to the shop floor.
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