725 and 730 Articulated Trucks Steering, Suspension, and Body Hoist Hydraulic Systems Caterpillar

Before troubleshooting, ensure that the system contains the corrected amount of the oil which is specified in the Operation and Maintenance Manual, SEBU7347.

The machine has lost steering capabilities.

If the machine has lost steering capabilities, the likely cause is a blockage or a leakage within the steering system. If oil flow is blocked, the maximum system pressure may still be achieved. If there is a leak in the steering system, it may not be possible to achieve the maximum system pressure that is specified.

Possible Causes

1. There is a leak within the steering system, which could be an external leak or an internal leak within a component. An external leak will be visible. An internal leak will result in an increased oil flow to the tank from the leaking component. The piston pump (steering), the metering pump, and the steering cylinders are capable of leaking internally.

2. The steering wheel cannot be rotated. This could be caused by a mechanical binding within the metering pump or by a problem with the steering column.
   • Refer to Systems Operation, Testing and Adjusting, "Metering Pump (Steering) - Test".

3. There is a problem with the pressure and flow compensator valve, which is part of the piston pump (steering).

   1. The system pressure may be set too low.
      • Refer to Systems Operation, Testing and Adjusting, "Piston Pump (Steering) - Test and Adjust".

   2. The internal components of the pressure and flow compensator valve are damaged.
      • Refer to Disassembly and Assembly, RENR3447 for information on the piston pump (steering).

4. There is a problem with the signal and pressure reducing valve.(S/N: AXF1-866) and (S/N: AGF1-803)

   1. An orifice, which is inside of the signal and pressure reducing valve may be blocked. This may cause the signal and pressure reducing valve to block oil flow between the piston pump (steering) and the steering check and combiner valve.
      • Refer to Systems Operation, Testing and Adjusting, "Signal and Pressure Reducing Valve (Steering) - Check".

5. There is a problem with the steering check and combiner valve.

   1. One of the check valves may be restricting oil flow to the metering pump.
      • Refer to Disassembly and Assembly, RENR3447 and Specifications, RENR3485 for information on the steering check and combiner valve.

6. There is a problem with the metering pump.

   1. The metering pump may be directing oil to the tank instead of directing oil to the steering cylinders. This may result in reduced system pressure.
      • Refer to Systems Operation, Testing and Adjusting, "Piston Pump (Steering) - Test and Adjust" for information on testing the system pressure.

   2. The metering pump may be blocking oil between the steering check and combiner valve and the steering cylinders.

   3. The metering pump may not be producing the correct flow into the load sensing line. This will affect the flow from the piston pump (steering).

7. There is a problem with the steering cylinders.

   1. There may be mechanical damage to one or both of the steering cylinders. This could include damage to the seals.
      • Refer to Disassembly and Assembly, RENR3447 for information on the steering cylinders.

   2. A relief valve, which is attached to a steering cylinder, may be stuck open. This may result in reduced system pressure.

8. There is a problem with the piston pump (steering).

   1. Mechanical damage may prevent the piston pump (steering) from upstroking.

   2. Excessive internal leakage may result in decreased pump flow to the steering system.

The machine articulates slowly or articulation stops when resistance is encountered.

If the machine has lost steering capabilities, the likely cause is a restriction or a leakage within the steering system. If oil flow is restricted, the maximum system pressure may be achieved but the response time of the system will be slower. If there is a leak in the steering system, it may not be possible to achieve the maximum system pressure that is specified.

Possible Causes

1. There is a leak within the steering system, which could be an external leak or an internal leak within a component. An external leak will be visible. An internal leak will result in an increased oil flow to the tank from the leaking component. The piston pump (steering), the metering pump, and the steering cylinders are capable of leaking internally.

2. There is a problem with the pressure and flow compensator valve, which is part of the piston pump (steering).

   1. The system pressure may be set too low.
      • Refer to Systems Operation, Testing and Adjusting, "Piston Pump (Steering) - Test and Adjust".

   2. The internal components of the pressure and flow compensator valve are damaged.
      • Refer to Disassembly and Assembly, RENR3447 for information on the piston pump (steering).

3. There is a problem with the signal and pressure reducing valve. (S/N: AXF1-866) and (S/N: AGF1-803)

   1. An orifice, which is inside of the signal and pressure reducing valve may be blocked. This may cause the signal and pressure reducing valve to block oil flow between the piston pump (steering) and the steering check and combiner valve.
      • Refer to Systems Operation, Testing and Adjusting, "Signal and Pressure Reducing Valve (Steering) - Check".

4. There is a problem with the steering check and combiner valve.

   1. The check valve, which is connected to the piston pump (steering), may be causing a restriction.
      • Refer to Disassembly and Assembly, RENR3447 and Specifications, RENR3485 for information on the steering check and combiner valve.

5. There is a problem with the metering pump.

   1. The metering pump may be directing oil to the tank instead of directing oil to the steering cylinders. This may result in reduced system pressure.
      • Refer to Systems Operation, Testing and Adjusting, "Piston Pump (Steering) - Test and Adjust" for information on testing the system pressure.

   2. The metering pump may be blocking oil between the steering check and combiner valve and the steering cylinders.

   3. The metering pump may not be producing the correct flow into the load sensing line. This will affect the flow from the piston pump (steering).

6. There is a problem with the steering cylinders.

   1. There may be mechanical damage to one or both of the steering cylinders. This could include damage to the seals.
      • Refer to Disassembly and Assembly, RENR3447 for information on the steering cylinders.

   2. A relief valve, which is attached to a steering cylinder, may be stuck open. This may result in reduced system pressure.

7. There is a problem with the piston pump (steering).

   1. Mechanical damage may prevent the piston pump (steering) from upstroking.

   2. Excessive internal leakage may result in decreased pump flow to the steering system.

The steering wheel is difficult to turn.

Possible Causes

If the steering wheel is difficult to turn, the likely cause is insufficient oil flow to the metering pump or from the metering pump. This may be caused by a leakage or a blockage within the steering system.

1. The operator is turning the steering wheel faster than the maximum rate of steering.
   • Refer to Systems Operation, Testing and Adjusting, "Operational Checks" for the specified steering time.

2. The oil is cold.
   • Refer to Systems Operation, Testing and Adjusting, "General Information" for information on warming the oil.

3. There is a leak within the steering system, which could be an external leak or an internal leak within a component. An external leak will be visible. An internal leak will result in an increased oil flow to the tank from the leaking component.

4. The steering wheel cannot be rotated. This could be caused by a mechanical binding within the metering pump or by a problem with the steering column.
   • Refer to Systems Operation, Testing and Adjusting, "Metering Pump (Steering) - Test".

5. There is a problem with the pressure and flow compensator valve, which is part of the piston pump (steering).

   1. The system pressure may be set too low.
      • Refer to Systems Operation, Testing and Adjusting, "Piston Pump (Steering) - Test and Adjust".

   2. The internal components of the pressure and flow compensator valve are damaged.
      • Refer to Disassembly and Assembly, RENR3447 for information on the piston pump (steering).

6. There is a problem with the signal and pressure reducing valve. (S/N: AXF1-866) and (S/N: AGF1-803)

   1. An orifice, which is inside of the signal and pressure reducing valve may be blocked. This may cause the signal and pressure reducing valve to block oil flow between the piston pump (steering) and the steering check and combiner valve.
      • Refer to Systems Operation, Testing and Adjusting, "Signal and Pressure Reducing Valve (Steering) - Check".

7. There is a problem with the steering check and combiner valve.

   1. The check valve, which is connected to the piston pump (steering), may be causing a restriction.
      • Refer to Disassembly and Assembly, RENR3447 and Specifications, RENR3485 for information on the steering check and combiner valve.

8. There is a problem with the metering pump.

   1. The metering pump may be directing oil to the tank instead of directing oil to the steering cylinders. This may result in reduced system pressure.
      • Refer to Systems Operation, Testing and Adjusting, "Piston Pump (Steering) - Test and Adjust" for information on testing the system pressure.

   2. The metering pump may be blocking oil between the steering check and combiner valve and the steering cylinders.

   3. The metering pump may not be producing the correct flow into the load sensing line. This will affect the flow from the piston pump (steering).

9. There is a problem with the steering cylinders.

   1. There may be mechanical damage to one or both of the steering cylinders. This could include damage to the seals.
      • Refer to Disassembly and Assembly, RENR3447 for information on the steering cylinders.

   2. A relief valve, which is attached to a steering cylinder, may be stuck open. This may result in reduced system pressure.

10. There is a problem with the piston pump (steering).

    1. Mechanical damage may prevent the piston pump (steering) from upstroking.

    2. Excessive internal leakage may result in decreased pump flow to the steering system.

11. The check valve, which is in the tank line from the metering pump, will not open. This will block return flow from the metering pump.
    • Refer to Systems Operation, Testing and Adjusting, "Steering System" for the location of the check valve.

The steering is jerky.

Possible Causes

1. There is air in the steering system.
   • Refer to Systems Operation, Testing and Adjusting, "Visual Inspection".

2. There is a problem with the pressure and flow compensator valve, which is part of the piston pump (steering).

   1. The spool may be sticking due to damage or contamination.
      • Refer to Disassembly and Assembly, RENR3447 for information on the piston pump (steering).

3. The spool within the signal and pressure reducing valve may be sticking due to damage or contamination. (S/N: AXF1-866) and (S/N: AGF1-803)
   • Refer to Systems Operation, Testing and Adjusting, "Signal and Pressure Reducing Valve (Steering) - Check".

4. There is a problem with the metering pump.

   1. The spool is sticking due to damage or contamination.

5. There is a problem with one of the components in the load sensing system.
   • Refer to Systems Operation, Testing and Adjusting, "Load Sensing Pressure - Test".

6. There is a problem with the check valve in the tank line from the metering pump.
   • Refer to Systems Operation, Testing and Adjusting, "Steering System" for the location of the check valve.

The machine will not maintain the straight ahead position.

Possible Causes

1. There is a problem with the metering pump.

   1. The centering spring is broken.

   2. The spool is sticking due to damage or contamination.

   3. There is a problem with a check valve or a relief valve within the metering pump.
      • Refer to systems Operation, Testing and Adjusting, "Metering Pump (Steering) - Test".

2. There is a problem with one or both of the steering cylinders.

   1. The seals are damaged.

   2. One of the relief valves, which is attached to the steering cylinders, is leaking.

3. The tire pressures are incorrect.

The electric drive pump (secondary steering) does not stay on.

Possible Causes

1. A check valve in the steering check and combiner valve is stuck open.

2. A check valve in the load sensing line is stuck open. This check valve is located in the line between the signal and pressure reducing valve and the metering pump. (S/N: AXF1-866) and (S/N: AGF1-803)
   • Refer to Systems Operation, Testing and Adjusting, "Steering System" for the location of the check valve.

3. There is a problem with the pressure switch which activates the electric drive pump.
   • Refer to Systems Operation, Testing and Adjusting, "Steering System" for information about the pressure switch.

4. There is a problem with the electrical connections between the following components and the power train ECM.
   • There is a problem with the electric drive pump.

   • The pressure switch in the steering check and combiner valve is not operational.

The electric drive pump (secondary steering) does not supply the correct pressure.

Possible Causes

1. There is a problem with the electric drive pump.

   1. The relief valve, which is inside the electric drive pump, is stuck open.

   2. The motor is faulty.

2. A check valve in the load sensing line is stuck open. This check valve is located in the load sensing port of the signal and pressure reducing valve. (S/N: AXF1-866) and (S/N: AGF1-803)
   • Refer to Systems Operation, Testing and Adjusting, "Steering System" for the location of the check valve.

3. There is a problem with the steering check and combiner valve.

   1. One of the check valves may be restricting oil flow to the metering pump.
      • Refer to Disassembly and Assembly, RENR3447 and Specifications, RENR3485 for information on the steering check and combiner valve.

4. There is a problem with the metering pump.

   1. The metering pump may be directing oil to the tank instead of directing oil to the steering cylinders. This may result in reduced system pressure.
      • Refer to Systems Operation, Testing and Adjusting, "Piston Pump (Steering) - Test and Adjust" for information on testing the system pressure.

   2. The metering pump may be blocking oil between the steering check and combiner valve and the steering cylinders.

   3. The metering pump may not be producing the correct flow into the load sensing line. This will affect the flow from the electric drive pump.

5. There is a problem with the steering cylinders.

   1. There may be mechanical damage to one or both of the steering cylinders. This could include damage to the seals.
      • Refer to Disassembly and Assembly, RENR3447 for information on the steering cylinders.

   2. A relief valve, which is attached to a steering cylinder, may be stuck open. This may result in reduced system pressure.