Hydraulic System Troubleshooting Wheel Loader 966F Series II

 

 

 

 

 

 

 

 

S/N - 1SL1-UP
S/N - 3XJ1-UP
S/N - 4YG1-UP
S/N - 8BG1-UP
S/N - 9YJ1-UP

The main hydraulic pump relief valve is common to the circuits. The lift circuit and the tilt circuit have
load check valves in the head end circuit and in the rod end circuit in order to prevent cylinder drift
during movement of the valve spool.
The line relief valves in the lift circuit and in the tilt circuit protect the components from pressures in the circuits when the control valves are in the HOLD position.

• The oil pressure for opening the relief valves for the main system and for the line circuits must be within the specifications. Pressures that are too low will cause a decrease in the lifting force and in the dig characteristics. Pressures that are too high will cause a decrease in the life of hoses and of other components.
• Circuit drift is caused by leakage past cylinder pistons, past O-ring seals in the control valves, past
  load check valves that do not seat correctly or past makeup valves that do not seat correctly. Poor
  adjustments of the control valves or incorrect fit may also contribute to circuit drift.
• Cycle times that are longer than normal result from oil leakage, from pump wear, or from the
  pump speed.

Note: If this machine is equipped with an implement electronic control module  the fault codes

can be displayed on the message area of the message center when a system event occurs. Make sure that
all faults are corrected before you troubleshoot the following problems.

Problem: The implement pump makes noise and the cylinder rods do not move evenly. There are
also air bubbles in the oil.

Probable causes:
1. The viscosity of the oil is incorrect.
2. The main relief valve opens at low oil pressure.
3. There is a loose connection of the oil line on the inlet side of the implement pump.
4. The implement pump has too much wear.

Problem: The oil temperature is too high.

Probable causes:
  1. The machine is being operated above the intended capacity or in ambient temperatures that are too
     high for the machine's design.
  2. The viscosity of the oil is incorrect.
  3. The setting of the main relief valve is too low. This causes the main relief valve to remain open.
  4. The implement pump has too much wear.
  5. There is a restriction in an oil passage.
  6. There is a leak in one or more circuits.
  7. The oil level is low.
  8. The oil is contaminated.
  9. The air flow through the hydraulic oil cooler is too low.
10. The oil flow through the hydraulic oil cooler is too low.
11. There is air in the hydraulic oil.

Note: A problem with air in the hydraulic oil must be corrected before the hydraulic system will
operate at normal temperatures. There are two conditions that cause air to be in the hydraulic oil:

• Return oil is flowing into the hydraulic oil tank above the level of oil that is in the tank.
•  There are leaks in the oil suction line between the implement pump and the hydraulic oil tank

12. The recirculation seals are damaged or missing. This allows hot air to recirculate upstream of the
       hydraulic oil cooler.
13. The hydraulic oil temperature sensor is faulty.

Problem: The output of the implement pump is low.

Probable causes:
1. The oil level is low.
2. The viscosity of the oil is incorrect.
3. The implement pump has too much wear.

Problem: The oil pressure is low.
 
Probable causes:
1. The main relief valve opens at low oil pressure.
2. The implement pump has too much wear.
3. An O-ring seal in the system failed.
4. The main control valve and the valve spool have an excessive amount of wear.

Problem: The attachment moves while the control lever is in the HOLD position.
 
Probable causes:
1. The pilot control actuator on the main control valve is damaged.
2. The control valve and the valve spool have an excessive amount of wear.
3. A piston seal in a cylinder has an excessive amount of wear.
4. There is a leak in a connection between the control valve and the moving cylinder(s).
5. A load check valve is not closing because of dirt or because of a worn seat.
6. The control valve is not centering correctly.

Problem: The attachment droops when the lift control lever is moved from the HOLD position to the RAISE position.

Probable causes:
1. The oil is too cold.
2. The piston seals and/or the lift cylinders are worn.
3. The load check valve is not closing because the return spring is weak or broken, or because there
     is dirt or debris in the load check valve.

Problem: The hydraulic force is too low when the lift control lever is moved to the RAISE position or to the LOWER position.

Probable causes:
1. The machine is being operated incorrectly.
2. The pilot system pressure is too low.
3. The modulation current to the solenoid for the pilot control actuator is not correct.
4. The main control valve is contaminated or damaged.
5. The load check valve is not closing because the return spring is weak or broken, or because there
     is dirt or debris in the load check valve.
6. The pilot control valve is contaminated or damaged.
7. The main relief valve setting is too low.

Problem: All implement functions are sluggish.

Probable causes: 
1. The oil level is too low.
2. One or both of the implement pumps is worn or damaged.
3. One or both of the main relief valve settings is too low.
4. The pilot relief valve is faulty or the pressure setting for the pilot relief valve is too low.
5. The oil in the hydraulic system is contaminated.

Problem: The implement functions are erratic or intermittent.

Probable causes:
1. The oil level is too low.
2. There is air in the hydraulic oil.

Note: A problem with air in the hydraulic oil must be corrected before the hydraulic system will
operate at normal temperatures. There are two conditions that cause air to be in the hydraulic oil:

•  Return oil is flowing into the hydraulic oil tank above the level of oil that is in the tank.
•  There are leaks in the oil suction line between the hydraulic pump and the tank.

3. One or both of the pumps has too much wear.
4. The modulation current to the solenoid for the pilot control actuator is not correct.
5. The pilot relief valve is faulty or the pressure setting for the pilot relief valve is too low.
6. The main control valve is contaminated or damaged.
7. The load check valve is not closing because the spring is weak or broken, or because there is dirt
    or debris in the load check valve.

Problem: There is too much lift cylinder drift.

Probable causes:
1. The modulation current to the solenoid for the pilot control actuator is incorrect.
2. The ride control diverted valve is worn or damaged.
3. The relief valve setting for the ride control valve is too low while the ride control switch is ON.
4. The piston seals and/or the lift cylinders are worn.
5. The components of the main control valve are worn or damaged.
6. The load check valve is not closing because the spring is weak or broken or because there is dirt
    or debris in the check valve.

Problem: The hydraulic force is too low when the tilt control lever is moved to the TILT BACK
position or to the DUMP position.

Probable causes:
1. The machine is being operated incorrectly.
2. The modulation current to the solenoid for the pilot control actuator is incorrect.
3. The pilot relief valve is faulty or the pressure setting for the pilot relief valve is too low.
4. The settings of the line relief valves are too low.
5. The piston seals and/or the lift cylinders are worn.
6. The main control valve is contaminated or damaged.
7. The pilot control actuator is contaminated or damaged.
8. The main relief valve setting is too low.

Problem: The lift cylinders collapse during the lift operation.

Probable causes:
1. The pilot relief valve is faulty or the pressure setting for the pilot relief valve is too low.
2. The ride control divert er valve may be worn or damaged.
3. The relief valve setting for the ride control valve is too low while the ride control switch is ON.
4. The nitrogen recharger pressure in the ride control accumulator is too low.
5. The piston seals and/or the lift cylinders are worn.
6. The main control valve is contaminated or damaged.
7. The load check valve is not closing because the spring is weak or broken, or because there is dirt
     or debris in the check valve.

Problem: There is low power to the implements.

Probable causes:
1. The machine is operating above the intended capacity.
2. The engine power is too low.
3. The implement pump has too much wear.
4. The modulation current to the solenoid for the pilot control actuator is incorrect.
5. The pilot relief valve is faulty or the pressure setting for the pilot relief valve is too low.
6. One or both of the main relief valve settings is too low.
7. The settings of the line relief valves are too low.
8. The piston seals and/or the cylinders are worn.
9. The load check valve is damaged or contaminated.

Problem: There is too much tilt cylinder drift.

Probable causes:
1. The modulation current to the solenoid for the pilot control actuator is incorrect.
2. The setting of the line relief valve is too low.
3. The piston seals and/or the tilt cylinder is worn.
4. The components of the main control valve are worn or damaged.
5. The load check valve is contaminated or damaged.

Problem: The tilt cylinder collapses during the tilt operation.

Probable causes:
1. The modulation current to the solenoid for the pilot control actuator is incorrect.
2. The setting of the tilt cylinder relief valve is too low.
3. The piston seals and/or the tilt cylinder is worn.
4. There is dirt or debris in the main control valve.
5. The main control valve spool and mating surfaces may be worn or damaged.
6. The makeup valve is sticking.

Problem: The bucket droops during the tilt function.

Probable causes:
1. The oil is too cold.
2. The piston seals and/or the lift cylinder is worn.
3. The load check valve is not closing because the spring is weak or broken, or because there is dirt
    or debris in the check valve.

Problem: One implement function is sluggish or nonfunctional.

Probable causes:
1. The modulation current to the solenoid for the pilot control actuator is incorrect.
2. The setting of the line relief valve is too low.
3. The spool in the ride control diverted valve and the mating surfaces are worn or damaged.
4. The main control valve spool and the mating surfaces are worn or damaged.

Problem: The implements are not functioning.
 
Probable causes:1. The pilot pressure supply solenoid valve is not energized or the solenoid valve is malfunctioning.
2. The pilot pump is worn or damaged.
3. The implement pump has too much wear.
4. The pilot relief valve is faulty or the pressure setting for the pilot relief valve is too low.
5. The dead engine manual lower valve is open.
6. The main relief valve setting is too low.