938G Series II Wheel Loader and IT38G Series II Integrated Toolcarrier Hydraulic System Caterpillar

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Personal injury or death can result from sudden machine movement. Sudden movement of the machine can cause injury to persons on or near the machine. To prevent injury or death, make sure that the area around the machine is clear of personnel and obstructions before operating the machine.

Machine Preparation For Troubleshooting

1. Park the machine on a smooth, level surface. Park the machine away from working machines and personnel. Lower the work tool to the ground.

2. Allow only one operator on the machine. Keep all personnel away from the machine or in the view of the operator.

3. Move the transmission control lever to the NEUTRAL position.

4. Engage the parking brake.

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Illustration 1	g00926858

5. Place the steering frame lock in the LOCKED position.

   Reference: For more information about preparing the machine for troubleshooting, refer to the Service Manual module Testing and adjusting, "General Testing and Adjusting Information" for the machine that is being serviced.

Torque Converter Stall and Double Stall Test

The torque converter stall test helps determine if the engine is producing the correct power output. The torque converter stall test provides an engine speed for comparison with the engine speed from the double stall test. This stall test is used in many diagnostic procedures.

The service brakes must be applied when the tests are performed. Make sure that the service brakes and the parking brake are fully operational before you perform any tests.

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Illustration 2	g00925511
Location of the Tap for the Torque Converter Outlet Pressure

1. Install a 8T-0848 Pressure Gauge 0 to 400 kPa (0 to 58 psi) from 1U-5481 Pressure Gauge Group on the pressure tap for the torque converter outlet pressure. Run the hose assembly into the cab in order to read the torque converter outlet pressure while you run the stall test and implement double stall test.

   Note: If the machine is equipped with remote pressure taps, install a pressure gauge on number 6 pressure tap. Number 6 is the tap for the torque converter outlet pressure. The remote pressure taps are located under the cover behind the ladder on the left side of the machine.

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Illustration 3	g00925248
Solenoid Valve (Hydraulic Fan)

2. Set the hydraulic fan to the maximum rpm. In order to run the hydraulic fan system at the maximum rpm, the connection to the solenoid valve for the hydraulic fan system must be disconnected.

   Note: The solenoid valve is located on the right side of the engine and to the right of the hydraulic fan pump. Turn the engine start switch to the OFF position. Disconnect the electrical connection from the connection on the solenoid valve.

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Illustration 4	g00925252
Switch Panel

3. Place the transmission neutralizer in the OFF position by depressing the top of the switch.

4. The following table gives the speed and direction control for the machines that are listed.
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   Table 2

   Speeds For The Torque Converter Stall And Implement Double Stall
   Machine	Torque Converter Stall Speeds	Double Stall Speeds
   938G Series II IT38G Series II Fourth Gear (1)	2085 ± 65 rpm	1705 ± 65 rpm
   938G Series II IT38G Series II First Gear (1)	2015 ± 65 rpm	1705 ± 65 rpm

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   ( 1 )

   The 962G II machine has dual horsepower. The machine must be tested in both FOURTH SPEED FORWARD and FIRST SPEED FORWARD. The difference between the fourth speed forward and the first speed forward must be at least 40 rpm.

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   Table 3

   Torque Converter Oil Temperature For The Stall Tests (1)
   Machine	Temperature
   938G Series II IT38G Series II	76 °C (168 °F) to 112 °C (230 °F)

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   ( 1 )

   The temperature of the torque converter oil is measured at the torque converter outlet. Refer to Illustration 5 for the screed in order to read the temperature at the torque converter outlet in Cat ET.

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Illustration 5	g00934339

5. Engage the parking brake. Start the engine and run the engine at high idle. Ensure that the oil for the torque converter output is at the normal operating temperature. Refer to Table 3 for normal operating temperature of the machine that is being serviced. This temperature is measured at the torque converter outlet. If Caterpillar Electronic Technician is being used, the oil temperature for the torque converter outlet can be monitored on the screen through Caterpillar ET.

6. Ensure that the work tool is positioned on the ground.

7. Reduce the engine speed to low idle.

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Illustration 6	g00925262
Dash Panel Location of the Digital Tachometer

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NOTICE
To ensure that the transmission oil does not overheat, do not keep the torque converter in a full stall condition for more than 30 seconds. After the torque converter stall test, reduce the engine speed to low idle. In order to cool the oil, move the transmission control to the NEUTRAL position and run the engine between 1200 rpm and 1500 rpm.

8. Fully depress the right side service brake pedal. Shift the transmission direction and speed control to the position that is referred to into the FOURTH SPEED FORWARD position. Hold the right service brake pedal in the depressed position for the duration of the test.

   Note: Do not use the left brake pedal as a service brake.

9. Press the governor control pedal to full travel. Allow the engine rpm to stabilize. Then, observe the tachometer. Record the engine rpm. Refer to Table 2 for the correct torque converter stall speed for fourth speed forward. The torque converter outlet pressure should be at least 275 kPa (40 psi).

10. Set the engine to low idle. Shift the transmission direction and speed control into NEUTRAL position.

11. The 938G Series II Wheel Loader and the IT38G Series II Integrated Toolcarrier should be tested in First Speed Forward.

12. With the engine in low idle, shift the transmission direction and speed control to the position that is referred to into the FIRST SPEED FORWARD position.

    Note: While the parking brake is applied,the following procedure is used in order to engage the power train in the FIRST SPEED FORWARD position. Move the transmission direction and speed control to the NEUTRAL position. Select the FIRST SPEED position on the transmission direction and speed control. Move the transmission and speed control to the FORWARD position. Then move the transmission direction and speed control to the NEUTRAL position, and finally move the transmission direction and speed control back to the FORWARD position.

13. Slowly depress the governor control pedal to full travel. Allow the engine rpm to stabilize. Then, observe the tachometer. Record the engine rpm. Refer to Table 2 for the correct torque converter stall speed for first speed forward. Record the result. The difference between fourth speed forward and first speed forward should be at least 40 rpm different.

14. Set the engine to low idle. Shift the transmission direction and speed control into NEUTRAL position.

    Reference: To check the performance of the Caterpillar 3126B Engine, refer to the following service literature: Specifications, SENR9579, "3126B Engine For Caterpillar Built Machines", Troubleshooting, RENR2370, "3126B Engine For Caterpillar Built Machines" and Systems Operation, Testing and Adjusting, SENR9580, "3126B Engine For Caterpillar Built Machines".

    Note: The results of the torque converter stall test must be within specifications before the double stall test can be performed.

    The double stall test is used in order to determine the performance of the implement pump. This stall test is also used in other diagnostic procedures.

15. Ensure that the transmission direction and speed control is in the NEUTRAL position. Allow the engine coolant and the transmission oil to cool. Wait at least two minutes between tests in order to allow the transmission oil to cool.

16. Ensure that the oil for the torque converter output is at the normal operating temperature. Refer to Table 3 for the normal operating temperature of the machine that is being serviced. Refer to Illustration 5 of the screen from Caterpillar Electronic Technician.

17. Position the work tool in the full TILT BACK position.

18. Fully depress the right side service brake pedal. Shift the transmission direction and speed control to the position that is referred to into the FOURTH SPEED FORWARD position. Hold the right serviced brake pedal in the depressed position for the duration of this test. Ensure that the parking brake is applied. Ensure that the transmission neutralizer override switch is in the ON position.

19. Slowly, depress the governor control pedal to full travel. Allow the engine rpm to stabilize.

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NOTICE
To ensure that the transmission oil does not overheat, do not keep the torque converter in a full stall condition for more than 30 seconds. After the torque converter stall test, reduce the engine speed to low idle. In order to cool the oil, move the transmission control to the NEUTRAL position and run the engine between 1200 rpm and 1500 rpm.

20. Move the tilt control lever to the full TILT BACK position and hold the lever in this position. Refer to Table 2 for the correct double stall speed for fourth speed forward. Then, observe the tachometer. Record the engine rpm.

    Note: For the 938G Series II Wheel Loader and the IT38G Series IIIntegrated Toolcarrier, the torque converter stall test and the double stall should be done with the transmission in fourth speed forward. Also, the torque converter stall and implement pump double stall test should be tested in first speed forward.

21. Set the engine to low idle. Shift the transmission direction and speed control into NEUTRAL position.

22. Ensure that the transmission direction and speed control is in the NEUTRAL position. Allow the engine coolant and the transmission oil to cool. Wait at least two minutes between tests in order to allow the transmission oil to cool.

    Note: While the parking brake is applied,the following procedure is used in order to engage the power train in the FIRST SPEED FORWARD position. Move the transmission direction and speed control to the NEUTRAL position. Select the FIRST SPEED position on the transmission direction and speed control. Move the transmission and speed control to the FORWARD position. Then move the transmission direction and speed control to the NEUTRAL position, and finally move the transmission direction and speed control back to the FORWARD position.

23. With the engine in low idle, shift the transmission direction and speed control to the position that is referred to into the FIRST SPEED FORWARD position.

24. Slowly, depress the governor control pedal to full travel.

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NOTICE
To ensure that the transmission oil does not overheat, do not keep the torque converter in a full stall condition for more than 30 seconds. After the torque converter stall test, reduce the engine speed to low idle. In order to cool the oil, move the transmission control to the NEUTRAL position and run the engine between 1200 rpm and 1500 rpm.

25. Move the tilt control lever to the full TILT BACK position and hold the lever in this position. Allow the engine rpm to stabilize. Refer to Table 2 for the correct double stall speed for first speed forward. Then, observe the tachometer. Record the engine rpm.

26. Move the tilt control lever to the HOLD position. Reduce the engine speed to low idle. Shift the transmission direction and speed control to the NEUTRAL position.

27. Release the right side service brake pedal. Put the transmission neutralizer override switch into the OFF position.

    Turn the engine start switch to the OFF position. Connect the connector for the solenoid valve (hydraulic fan).

    Double stall speeds that are too low indicate improper performance for the implement pump. The pump must then be tested.