904B Wheel Loader Hydraulic and Steering System Caterpillar

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Personal injury or death can result from machine articulation or movement. Machine frames can move and a person can be crushed. Connect the steering frame lock link between the front and rear frames before working on machine.

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Personal injury or death can result from escaping fluid under pressure. Escaping fluid under pressure, even a very small pin-hole size leak, can penetrate body tissue and cause serious injury and possible death. If fluid is injected into your skin, it must be treated immediately by a doctor familiar with this type of injury. Always use a board or cardboard when checking for a leak.

This section provides probable causes to known problems. Prepare the machine for troubleshooting. Refer to Testing and Adjusting, "Machine Preparation for Troubleshooting". Perform a visual inspection of the machine. Refer to Testing and Adjusting, "Visual Inspection".

Operational Checks

Operate the machine in each direction and in all speeds. Note the noises that are not normal and find the sources of the noises. If the machine is not operating correctly, refer to "Troubleshooting Problem List".

Troubleshooting Problem List

1. The work tools are not functioning.

2. All work tool functions are sluggish.

3. The work tool functions are erratic or intermittent.

4. The work tool pump makes noise and the cylinder rods do not move evenly.

5. The oil temperature is too high.

6. The output of the work tool pump is low.

7. The oil pressure is low.

8. The work tool moves while the work tool control is in the HOLD position.

9. The work tool droops when the lift control is moved from HOLD to RAISE.

10. There is too much lift cylinder drift.

11. The work tool droops during the tilt function.

12. There is too much tilt cylinder drift.

13. The work tool will not lower to the ground when the engine is stopped.

Troubleshooting Probable Causes

Problem 1

The work tools are not functioning.

Probable causes

1. The switch for the hydraulic shutoff valve could be in the OFF position.

2. The hydraulic shutoff valve or wiring could be faulty.

3. The main relief valve setting could be too low.

4. The work tool pump could have too much wear.

5. The charge pump could have too much wear.

6. The pilot system pressure could be incorrect.

7. A pilot valve might not be functioning properly.

8. The priority valve spool is sticking.

9. The bank valve might not be functioning properly.

Problem 2

All work tool functions are sluggish.

Probable causes

1. The oil level could be low.

2. The work tool pump could be worn or damaged.

3. The charge pump could be worn or damaged.

4. The main relief valve setting could be too low.

5. The pilot system pressure could be incorrect.

6. A pilot valve might not be functioning properly.

7. The hydraulic system could be contaminated.

8. The priority valve spool is sticking.

9. The bank valve might not be functioning properly.

Problem 3

The work tool functions are erratic or intermittent.

Probable causes

1. The oil level could be low.

2. There could be 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 tank above the level of oil that is in the tank.

   • There are leaks in the oil suction line between the pump and the tank.

3. The work tool pump could be worn or damaged.

4. The charge pump could be worn or damaged.

5. The bank valve could be contaminated or damaged.

6. A load check valve might not be closing because a spring is weak or broken or because there is dirt or debris in the check valve.

7. The pilot system pressure could be incorrect.

8. A pilot valve might not be functioning properly.

Problem 4

The work tool pump makes noise and the cylinder rods do not move evenly.

Probable causes

1. The viscosity of the oil could be incorrect.

2. The main relief valve setting could be too low.

3. There could be a loose connection of the oil line on the inlet side of the pump.

4. The work tool pump could have too much wear.

Problem 5

The oil temperature is too high.

Probable causes

1. The machine might be being operated above the intended capacity.

2. The viscosity of the oil could be incorrect.

3. The main relief valve setting is too low.

4. The work tool pump could have too much wear.

5. There could be a restriction in an oil passage.

6. There could be a leak in one or more circuits.

7. The load on the system could be too high. This causes the relief valve to open.

8. The oil level could be too low.

9. The oil could be contaminated.

10. The flow of air through the oil cooler could be too low.

11. The oil flow through the oil cooler could be too low.

12. There could be 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 line between the hydraulic pump and the hydraulic oil tank.

13. The hydraulic oil temperature sensor could be faulty.

Problem 6

The output of the work tool pump could be too low.

Probable causes

1. The oil level could be too low.

2. The viscosity of the oil could be incorrect.

3. The work tool pump might have too much wear.

Problem 7

The oil pressure could be too low.

Probable causes

1. The main relief valve setting is too low.

2. The work tool pump might have too much wear.

3. An O-ring seal in the system could have failed.

4. The bank valve and the valve spool might have an excessive amount of wear.

Problem 8

The work tool moves while the control lever is in the HOLD position.

Probable causes

1. The bank valve and the valve spool could have an excessive amount of wear.

2. A piston seal in a cylinder could have excessive wear.

3. There could be a leak between the bank valve and the cylinder that is drifting.

4. A check valve might not be closing because of dirt or because of a worn seat.

5. The bank valve might not be centering correctly.

Problem 9

The work tool droops when the lift control is moved from HOLD to RAISE.

Probable causes

1. The oil could be too cold.

2. The piston seals of the lift cylinder could be worn.

Problem 10

There is too much lift cylinder drift.

Probable causes

1. The setting of the line relief valve could be too low.

2. The piston seals of the lift cylinder could be worn.

3. The components of the bank valve could be worn or damaged.

Problem 11

The work tool droops during the tilt function.

Probable causes

1. The oil could be too cold.

2. The piston seals and/or the tilt cylinder could be worn.

3. The load check valve might not be closing because the spring is weak or broken, or because there is dirt or debris in the check valve.

Problem 12

There is too much tilt cylinder drift.

Probable causes

1. The setting of the line relief valve could be too low.

2. The piston seals and/or the tilt cylinder could be worn.

3. The components of the bank valve could be worn or damaged.

4. A load check valve might not be closing because the spring is weak or broken, or because there is dirt or debris in the check valve.

Problem 13

The work tool will not lower to the ground when the engine is stopped.

Probable causes

1. The accumulator might be improperly charged.

2. The switch for the hydraulic shutoff valve could be in the OFF position.

3. The hydraulic shutoff valve or wiring could be faulty.