Specifications

Vehicle System Testing & Adjusting 49
Hydraulic System and Mast
Problem: The hydraulic system will not lift the load.
Probable Hydraulic Cause:
1. There is an air leak, which lets air into the
hydraulic system on the inlet side of the hydraulic
pump.
2. The relief valve opens at low oil pressure.
3. The hydraulic pump has too much wear.
4. The priority valve does not work correctly.
5. The load is not correct.
6. Unload function doesn’t work correctly.
Probable Mechanical Cause:
1. The mast is not in alignment with the other lifting
components and does not move freely.
2. Not enough lubricant on the parts of the mast
that move.
3. The carriage or mast rollers bearings are worn
and do not move (seized).
4. Mast shimmed too tight.
Problem: Lift cylinder extends too slowly.
Probable Hydraulic Cause:
1. Not enough oil supply to lift cylinder.
2. Defective lift cylinder seals.
3. Relif pressure ser too low.
4. Unload function doesn’t work correctly.
Problem: Mast does not move smoothly.
Probable Hydraulic Cause:
1. Air in the hydraulic system.
2. Relief valve sticks or defective.
3. Damaged cylinders.
Probable Mechanical Cause:
1. Not enough lubricant on the parts of the mast
that move.
2. Load rollers defective or not adjusted correctly.
3. Mast rollers not shimmed correctly.
4. Mast assembly is damaged or not in alignment.
Problem: The mast does not tilt correctly or moves
too slowly.
Problem Hydraulic Cause:
1. There is a restriction in the hydraulic tilt lines.
2. There is an air leak, which lets air into the
hydraulic system on the inlet side of the hydraulic
pump.
3. The relief valve opens at low oil pressure.
4. The hydraulic pump has too much wear.
5. The internal valve of the tilt spool is stuck
6. Control valve tilt spool has a restriction
7. The priority valve does not work correctly.
8. Seals in tilt cylinder worn or damaged.
9. Unload function doesn’t work correctly.
Provable Mechanical Cause:
1. Damage or failure of the tilt cylinders.
2. Mast mounting pins seized.