D6N Track-Type Tractor Hydraulic System Caterpillar

Problems that are Common to Both the Implement and Steering Systems

In this section, a problem that is common to the implement and steering systems will be highlighted. Possible causes of the problem will appear in a list below the problem.

The temperature of the oil is too high.

1. Oil cooler core is plugged or air flow over the core is low.

2. Wrong setting of the oil cooler bypass valve

3. Wrong oil viscosity

4. Excessive wear in the pump

5. Restriction in an oil passage

6. Excessive load on the system

7. Oil aeration

8. Low oil level

9. Wrong setting of flow compensator valve on the implement pump

10. High outside air temperature

11. A control valve spool is partially shifted.

12. The settings of the crossover relief/makeup valves on the steering pump are too low.

13. The pressure compensator valve for the steering pump is set too high.

14. The pressure compensator for the implement pump is set too high.

15. The setting of the charge relief valve for the steering charge pump is too high.

16. The oil passage in an active hydraulic circuit is restricted.

17. The setting for the margin pressure is too high.

18. A pump or a motor has excessive wear.

There is a large amount of air in the oil.

1. A suction line from the tank to a pump is leaking.

2. Low oil level

3. Leakage around cylinder seals

4. The hydraulic tank has a broken baffle.

The system is losing oil.

1. A hose or fitting is leaking.

2. The cylinder rod seals are leaking.

3. A seal on a pump shaft is leaking.

4. The seal on the motor shaft is leaking.

Implement System

In this section, a problem with the implement system will be highlighted. Possible causes of the problem will appear in a list below the problem.

The pump makes unusual noise. The cylinder rods do not move smoothly and there are air bubbles in the oil.

1. Wrong oil viscosity

2. Oil aeration

3. Excessive wear in the pump

4. Low oil level

The setting for low pressure standby is too low.

1. Low margin pressure

The setting for low pressure standby is too high.

1. High margin pressure

2. Signal pressure above zero

The margin pressure is too low.

1. Wrong setting of flow compensator valve

2. Broken spring in flow compensator valve

3. Malfunctioning pump

4. Wrong setting of pressure compensator valve

5. Broken spring in pressure compensator valve

6. Leak in the signal network

The margin pressure is too high.

1. Wrong setting of flow compensator valve

Pump discharge pressure is too high.

1. Wrong setting of pressure compensator valve

2. Malfunctioning pressure compensator valve

3. Malfunctioning pump

Pump discharge pressure is too low.

1. Wrong setting of pressure compensator valve

2. Broken spring in pressure compensator valve

3. Low setting of line relief valve

4. Leak in the signal network

There is a pause before pressure is reached in all circuits.

1. Air in the signal network

2. Dirt or debris in the resolver

Signal pressure is not zero when all valves are in the HOLD position.

1. Activated control lever

2. Pressure in signal network

Any attachment moves with the control levers in the HOLD position.

1. Excessive wear in the control valve

2. Wear in the cylinders

3. Leakage between the valve and the cylinders

The control stem on a valve will not shift into the body.

1. Contamination in the end housing

There is excessive drift in the attachments.

1. Wear in the cylinders

2. Leakage around a makeup valve

3. Incorrect position of spool in the main control valve

4. Excessive wear in the control valve

The attachments droop when the attachments are raised.

1. Air in the signal network

2. Dirt or debris in the resolver

3. Wrong setting of flow compensator valve

4. Broken spring in flow compensator valve

The cycle times of the attachments are too slow.

1. Leakage in the signal network

2. Incorrect setting of margin pressure

3. Malfunctioning pump

4. Leakage around piston seals and the cylinder

5. Leakage through the makeup valves in the control valves

6. Leakage in the control valve (worn valve section and worn spool)

The bulldozer blade moves upward while the control lever is in the HOLD position.

1. Malfunctioning makeup valve

The cycle times of the attachments are too fast.

1. Incorrect setting of margin pressure

There is too long of a pause at ground level before the bulldozer starts to raise.

1. Sticking restrictor spool

The line relief valves are too noisy.

1. Low setting of line relief valve

2. Broken spring in line relief valve

3. Wrong setting of pressure compensator valve

Steering System

In this section, a problem with the steering system will be highlighted. Possible causes of the problem will appear in a list below the problem.

The machine will not turn or the steering is very gradual.

1. The pump is not connected to the pump drive or the pump drive shaft is broken.

2. The oil level in the hydraulic tank is low.

3. The steering pump or the steering motor has failed.

4. There is no charge pressure or pilot pressure.

5. The parking brake is on. The problem is caused by one of the following reasons.
   • The oil pressure in the power train is low.

   • Internal leakage in the brake valve

   • The wiring has a fault.

6. There is a mechanical problem in the drive train.

The steering turn diameter is too large.

1. The charge pressure is low. The problem is caused by one of the following reasons.
   • The charge pump is damaged or worn.

   • The cold start valve is faulty.

   • The charge pressure relief valve is set too low.

   • There is high leakage at the motor flushing valve.

   • The steering pump or the steering motor has failed.

2. There is low pilot pressure. The problem is caused by one of the following reasons.
   • The steering control lever is improperly adjusted.

   • The pilot valves are improperly set.

   • There is excessive leakage in the pilot valve.

   • There is a blocked supply line to the pilot valve.

3. The steering pump has malfunctioned. The problem is caused by one of the following reasons.
   • The crossover relief/makeup valve is leaking.

   • The pump controls are misadjusted or faulty.

4. The steering motor has malfunctioned. The problem is caused by one of the following reasons.
   • The motor is worn or failed.

   • The flushing valve is faulty.

The steering turn diameter is too large in one direction.

1. There is low pilot pressure. The problem is caused by one of the following reasons.
   • The pilot valves are improperly adjusted.

   • There is excessive leakage on one side of the pilot valve.

   • There is a blocked pump signal line from the pilot valve.

2. The steering pump has malfunctioned. The problem is caused by one of the following reasons.
   • The crossover relief/makeup valve is leaking.

   • The pump is worn or failed.

3. The steering motor has malfunctioned. The problem is caused by one of the following reasons.
   • The motor is worn or failed.

   • The flushing valve is faulty.