904B Wheel Loader Power Train Caterpillar

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Personal injury or death can result from improperly checking for a leak. Always use a board or cardboard when checking for a leak. Escaping air or fluid under pressure, even a pin-hole size leak, can penetrate body tissue causing 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.

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Sudden movement of the machine or release of oil under pressure can cause injury to persons on or near the machine. To prevent possible injury, perform the procedure that follows before testing and adjusting the power train.

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Hot oil and components can cause personal injury. Do not allow hot oil or components to contact skin.

Note: The hydraulic lines and components must be hand cleaned. Use the same oil or use an equivalent oil that is in the machine. Install new filters. After the system has been flushed dispose of the fluid properly. Do not use mineral spirits, if biodegradable oil is used in the machine. If biodegradable oil is used in the machine, flush the machine with biodegradable oil only.

Filling the Hydrostatic System

1. Move the machine to a smooth, horizontal location. Move the machine away from other operating machines and away from personnel.

2. Lower the work tool to the ground. Stop the engine.

3. Engage the parking brake.

4. Connect the steering frame lock.

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Illustration 1	g01144424
Machine cab without the rubber floor mat and without the floorplate

5. Remove the rubber floor mat from the machine cab. Remove the floorplate from the machine cab.

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Illustration 2	g01172713
Test port location (1) SP (2) OS (3) PC (4) MH (5) CG or Fa (6) Port X2 (7) Port X1

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Illustration 3	g01160255
(9) PS for pump signal pressure

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Illustration 4	g01160611
(A) Cap for the hydraulic tank (B) Hydraulic oil level indicator

6. Remove the hydraulic tank filler cap (A) . Fill the pump and the motor through the test port (2) . Use the 6V-4143 Coupler and the 4C-9710 Hand Pump to fill the pump case. The hydraulic oil that is being added should be filtered and free of moisture. Pump hydraulic oil into the charge pump.

   Note: The rate of fill is 15 L/min (3.9626 US gpm). Do not exceed 4000 kPa (580 psi) in order to fill the charge circuit. Seal failure could result.

   Remove air from the pump case. Loosen the top port on the case. When oil appears from the port, the air is removed from the pump case.

7. Disconnect the linkage for the inching valve.

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Illustration 5	g01160611
(A) Cap for the hydraulic tank (B) Hydraulic oil level indicator

8. Fill the hydraulic tank until the oil level is full. Look at the hydraulic oil level indicator (B) on the right side of the machine. Add hydraulic oil until the hydraulic tank is full.

9. Install one 6V-4143 Coupler Assembly to each end of each 177-7860 Hose . Install 6V-3989 Unvalved Nipple to each pressure gauge. Install each pressure gauge to one end of each 177-7860 Hose .

10. The 8T-0846 Pressure Gauge has a range of 1000 kPa (144 psi). Install the pressure gauge and hose assembly to pressure tap (3) .

11. The 8T-0856 Pressure Gauge has a range of 6000 kPa (860 psi). Install the pressure gauge and hose assembly to pressure tap (5) .

12. The 8T-0856 Pressure Gauge has a range of 6000 kPa (860 psi). Install the pressure gauge and hose assembly to pressure tap (9) .

13. The 8T-0852 Pressure Gauge has a range of 40000 kPa (5800 psi). Install the pressure gauge and hose assembly to pressure tap (1) .

14. The 8T-0861 Pressure Gauge has a range of 60000 kPa (8700 psi). Install the pressure gauge and hose to test port (4) for the high pressure oil of the drive loop.

15. Clearly label the hydraulic test lines. Secure the hydraulic lines so that the pressure gauge can be viewed by the operator during the test. Do NOT hold the pressure gauge or the hydraulic line.

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Illustration 6	g01160460

16. Place all controls in the NEUTRAL position. Disconnect the wire (10) from the engine shutoff solenoid. Crank the engine. Do not start the engine. The pressure (5) should be 1500 kPa (218.0 psi).

    Note: Do not crank the engine for more than 20 seconds.

17. If the charge pressure is low, check the hydraulic oil level in the tank. Refill to the full mark. Use hydraulic oil that is clean and free of moisture. Determine the cause for low charge oil pressure before you restart the engine. When the charge pressure is correct, connect the wires to the engine shutoff solenoid.

18. Fasten the seat belt. Start the engine. Raise the work tool slightly.

19. Start the engine and run the engine at low idle.

20. Look at the pressure gauges. The charge oil pressure and the high pressure oil of the drive loop should be 3200 ± 300 kPa (460 ± 50 psi). The pressures should be reachedwithin 20 seconds of start-up. If the pressure is low, stop the engine. Check the hydraulic oil level in the tank. Determine the cause for low charge oil pressure before restarting the engine.

    Note: If charge pressure is not reached within 20 seconds, damage to the hydrostatic system will occur. Do not allow the hydrostatic system to operate with incorrect charge system pressures.

21. Start the engine and run the engine at low idle. Select the SLOW speed mode. Fully apply the service brakes and hold the service brakes. Disengage the parking brake.

22. Move the direction control lever to the FORWARD position.

23. Slowly increase engine speed until (4) AB (MH on Hystat pump) high pressure of the drive loop is 15000 ± 1000 kPa (2175 ± 145 psi). Hold the engine speed for one to two minutes. Return the engine speed to low idle.

    Note: This fills the motor cases.

24. Movement of the wheel is not permitted.

25. Move the direction control switch to the REVERSE position.

26. Slowly increase engine speed until (4) AB (MH on Hystat pump) high pressure of the drive loop is 15000 ± 1000 kPa (2175 ± 145 psi). Hold the engine speed for one to two minutes. Return the engine speed to low idle.

    Note: This fills the motor cases.

27. Movement of the wheel is not permitted.

28. Look at the hydraulic oil level indicator on the right side of the machine. Fill the hydraulic tank until the oil level is full.

Flushing The Hydrostatic System

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Hot oil and hot components can cause personal injury. Do not allow hot oil or hot components to contact skin.

After the failure of a component or after the replacement of a component, change all filters and clean all strainers. Refer to the Disassembly and Assembly for the procedure to disassemble the return block that is attached to the hydraulic tank.

If the oil becomes contaminated, premature component failure could result. Contaminated oil can also contribute to overheating. Use the following procedure to sample the oil in the system.

Flush the Implement Lines

1. Move the machine to a smooth, horizontal location. Move the machine away from other operating machines and away from personnel.

2. Lower the work tool to the ground. Stop the engine.

3. Engage the parking brake.

4. Connect the steering frame lock.

5. Sit in the seat and fasten the seat belt.

6. Apply the service brake.

7. Move the directional control lever to the NEUTRAL position. Engage the parking brake.

8. Press the speed select switch in the SLOW mode.

9. Start the engine and run the engine at low idle.

10. Increase the engine to high idle.

11. Move each attachment control lever one at a time to the FULL positions. Hold each attachment control lever for 7 to 13 seconds in the FULL position.

12. Decrease the engine speed to low idle. Apply the service brake pedal. Move the direction control lever to the NEUTRAL position. Engage the parking brake.

    Note: This flushes the implement lines.

Flush the Drive Lines

1. Remove the hydraulic tank filler cap (A) .

2. Install one end of the 177-7860 Hose Assembly to port (6) . Place the other end of the hose into the hydraulic tank filler neck.

3. Apply the parking brake and engage the service brakes.

4. Start the engine and set the engine speed to low idle.

5. Disengage the parking brake.

6. Place the direction control into the FORWARD position.

7. Slowly increase the engine speed to high idle.

8. Check that all air is purged from (6) X2 port.

9. Place the direction control into the NEUTRAL position.

10. Immediately remove the 177-7860 Hose Assembly from port (6) .

11. Install one end of the 177-7860 Hose As to port (7) . Place the other end of the hose into the hydraulic tank filler neck.

12. Apply the parking brake and engage the service brakes.

13. Start the engine and set the engine speed to low idle.

14. Disengage the parking brake.

15. Place the direction control into the REVERSE position.

16. Slowly increase the engine speed to high idle.

17. Check that all air is purged from (7) X1 port.

18. Place the direction control into the NEUTRAL position.

19. Immediately remove the 177-7860 Hose Assembly from port (7) .

21. Place the direction control into the FORWARD position.

22. Slowly increase the engine speed to high idle.

23. Disengage the parking brake.

24. Slowly increase the engine speed to high idle and hold the engine speed for 30 to 90 seconds.

25. Shift the direction control into the NEUTRAL position.

26. Repeat the test with the direction control lever in the REVERSE position.

    Note: This flushes the drive lines.

27. Purge the air from the load check valve on the pilot lines. Refer to Hydraulic and Steering System, Testing and Adjusting, RENR9760, "Load Control Valve Air (Lift and Tilt Cylinders) - Purge".

28. Reconnect the linkage for the inching valve.

Sampling the Hydraulic Oil

1. Operate the machine for a few minutes before obtaining the oil sample. Operate the hydraulic controls. This will thoroughly mix the hydraulic oil for a more accurate sample.

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Illustration 7	g01172713
Test port location (1) SP (2) OS (3) PC (4) MH (5) CG or Fa (6) Port X2 (7) Port X1

2. Use the sampling valve in order to obtain a sample of the hydraulic oil. The sampling valve is located on the left side of the machine behind the engine compartment (2) .

3. Move the directional control lever to the NEUTRAL position. Engage the parking brake.

4. Press the speed select switch in the SLOW mode.

5. Start the engine and run the engine at low idle.

6. Draw a 50 mL oil sample through the sampling port (2) . The level of contaminants must be lower than the values in the following table.

If the level of contaminants is higher than the values in the Table 3, repeat the flushing procedure. If the level of contaminants is higher than the values in the Table 3 again, change the filter elements and repeat the flushing procedure.

Reference: For more information, refer to Special Publication, SEBU6250, "Caterpillar Machine Fluids Recommendations" and Special Publication, PEHP6001, "How To Take A Good Oil Sample".