IT28G Integrated Toolcarrier and 924G, 924GZ and 928G Wheel Loaders Caterpillar

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Personal injury can result from hydraulic oil pressure and hot oil. Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic system. Make sure all of the attachments have been lowered, oil is cool before removing any components or lines. Remove the oil filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand.

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NOTICE
Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids. Refer to Special Publication, NENG2500, "Caterpillar Tools and Shop Products Guide" for tools and supplies suitable to collect and contain fluids on Caterpillar products. Dispose of all fluids according to local regulations and mandates.

On 924G and 924Gz machines, each of the valves have poppets which act as load check valves. The poppets close the ports so there is almost zero drift of the implements.

The relief valves in the auxiliary 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 auxiliary 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 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 can result from oil leakage, from pump wear, or from the pump speed.

If the basic tests indicate a leak in the circuit, install a flow meter and perform a test.

Problem List

1. The hydraulic power is low.

2. None of the functions will operate or all of the functions operate slowly.

3. The pilot oil pressure is low.

4. The pump will not reach high pressure cutoff.

5. The standby pressure cannot be adjusted correctly.

6. A hydraulic circuit is hammering.

7. You cannot lower the boom but you can raise the boom.

8. You cannot raise the boom and you cannot lower the boom.

9. You cannot tilt the bucket in either direction.

10. The oil temperature is too high.

11. There are air bubbles in the oil.

12. The cycle times are not correct.

13. The quick coupler does not operate.

14. The ride control function does not operate.

15. The implements will not lower with a dead engine.

16. The implements drift downward.

Probable Causes

Problem 1

The hydraulic power is low.

Probable Causes

1. Ensure that the engine is operating correctly. Perform the torque converter stall test.

2. The hydraulic oil is low. Check the hydraulic oil level.

3. The oil is not to the correct operating temperature. Check the oil temperature. Refer to "Problem 10".

4. There is air bubbles in the oil. Refer to "Problem 11".

5. The pilot oil pressure is low. Refer to "Problem 3".

6. The high pressure cutoff of the pump is low. Refer to "Problem 4".

7. The line relief valves are not set correctly.

8. Pilot control valves do not operate correctly.

9. The cylinders are leaking.

Problem 2

None of the functions will operate or all of the functions operate slowly.

Probable Causes

1. The switch for the hydraulic lockout that is on the right side of the seat is in the LOCK position. Move the switch to the UNLOCK position.

2. There is a leak in the system. Visually inspect the system for leaks in the system.

3. The pilot oil pressure is low. Refer to "Problem 3".

4. The high pressure cutoff of the pump for the work tools is not correct. Refer to "Problem 4".

5. The standby pressure is not set correctly. Refer to "Problem 5".

6. The throttle pin is stuck or damaged.

7. The inlet screen for the piston pump for the work tool is dirty. Drain the hydraulic tank. Inspect the inlet screen for contamination.

8. The pilot control valves are not operating correctly.

9. The seals in the cylinders are leaking.

10. The control valve is not operating correctly. Inspect the components of the valve for damage or for contamination.

11. The signal limiter valve is not adjusted correctly.

Problem 3

The pilot oil pressure is low.

Probable Causes

1. The setting for the pressure reducing valve is not correct.

2. The steering pump pressure for the low pressure standby pressure is not correct.

3. The signal drain valve is not functioning correctly.

4. The pressure reducing valve is contaminated. Loosen the adjusting screw on the pressure reducing valve and turn the screw inward.

Problem 4

The piston pump for the work tools will not reach high pressure cutoff.

Probable Causes

1. The oil level is low.

2. The viscosity of the oil is incorrect.

3. The oil is contaminated.

4. There is air in the oil. Refer to "Problem 11".

5. The cutoff spool is stuck. Loosen the adjusting screw for the cutoff spool and attempt to readjust the high pressure cutoff.

6. The load sensing relief valve is not adjusted correctly.

7. The pump may be worn.

Problem 5

The standby pressure cannot be adjusted correctly.

Probable Causes

1. The spring is damaged. Remove the margin spring and inspect the margin spring for damage.

2. The margin spool has damage or the margin spool has contamination. Remove the margin spool and inspect the margin spool.

Problem 6

A hydraulic circuit is hammering.

Probable Causes

1. There is air in the system. Refer to "Problem 11".

2. You are not using the machine correctly.

3. The line relief valves are not set correctly.

4. The margin pressure is not correct.

5. The pilot pressure is not set correctly.

Problem 7

You can not lower the boom but you can raise the boom.

Probable Causes

1. The ride control switch is in the ON position. Move the ride control switch to the OFF position.

2. You can not power up with the boom. Refer to "Problem 8".

3. The ride control valve is not working correctly.

4. The makeup valve in the lift valve is not working correctly. Disassemble the lift control valve.

Problem 8

You cannot raise the boom and you cannot lower the boom.

Probable Causes

1. None of the other functions are operating correctly. Refer to "Problem 2".

2. The lift cylinders have damage. Replace the cylinders.

3. The mechanical linkage of the boom has damage. Repair the damage.

4. The pilot control valve is not working correctly.

5. The ride control is not working correctly.

6. There is a failure in one of the seals of the lift cylinder.

7. The main control spool is stuck. Disassemble the valve and inspect the main control spool.

Problem 9

You cannot tilt the bucket in either direction.

Probable Causes

1. None of the other functions are operating correctly. Refer to "Problem 2".

2. The cylinders have damage. Repair the damage.

3. The line relief valves or the combination valve are not operating correctly. Check the settings for the line relief valves.

4. The pilot control valve is not working correctly.

5. The seals in one of the cylinders are leaking.

6. The main control spool is stuck. Disassemble the valve. Inspect the main control spool and inspect the springs.

Problem 10

The oil temperature is too high.

Probable Causes

1. The oil level is low.

2. The hydraulic oil cooler is plugged. Inspect the hydraulic oil cooler and clean the hydraulic oil cooler.

3. There is air in the hydraulic oil. Refer to "Problem 11".

4. The viscosity of the oil is incorrect.

5. The settings for the relief valve are too low.

6. The oil is contaminated. Replace the filter. Remove the cap from the hydraulic oil tank and inspect the sump screen.

Problem 11

There are air bubbles in the oil.

Note: A problem with air in the hydraulic oil must be corrected before the hydraulic system will operate at normal temperatures.

Probable Causes

1. There is a loose connection on the oil line on the inlet side of the pump. Visually inspect the supply lines of the pump for leaks and repair the leaks.

2. Return oil flows into the hydraulic tank above the level of oil that is in the tank. The oil level is low.

3. The cylinders are cavitating because the back pressure valve is not maintaining pressure in the return passages in the bank valve.

4. A makeup valve in the lift control valve or the tilt control valve is not opening. Inspect the lines that connect the bank valves to the cylinders for damage.

Problem 12

The cycle times are not correct.

Probable Causes

1. The pump has too much wear.

2. The standby pressure is not set correctly.

3. The main control spool may be sticking.

4. An O-ring seal in the system failed.

Problem 13

The quick coupler does not operate.

Probable Causes

1. The quick coupler switch is faulty.

2. The solenoid valve for the quick coupler does not operate correctly.

3. The steering pump does not operate correctly.

Problem 14

The ride control function does not operate.

Probable Causes

1. The ride control switch is faulty.

2. The ride control solenoid valve is not functioning correctly.

3. The ride control accumulator is not charged properly.

4. The valve for the dead engine lower is open.

Problem 15

The implements will not lower with the valve for the dead engine lower.

Probable Causes

1. The solenoid valve for the float function is not functioning correctly.

2. The valve for the dead engine lower is open.

3. The pilot lock valve is not functioning correctly.

Problem 16

The implement drifts downward.

Probable Causes

1. The pilot accumulator is not charged correctly.