TH103 Telehandler Steering System Caterpillar

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Personal injury can result from removing hoses or fittings in a system under pressure. Failure to relieve pressure can cause personal injury. Do not remove or disconnect hoses or fittings until all pressure in the hydraulic system has been relieved.

Illustration 1	g00743210
(1) Bank valve (2) Pump

Illustration 2	g01176860
(1) Bank valve (2) Piston pump (3) Test fitting (5) Signal relief valve (6) Pressure and flow compensator (20) Test fitting

Illustration 3	g01175789
(4) Test fitting

Note: Refer to Testing and Adjusting, "Steering System Troubleshooting" before you begin this procedure.

All points for testing and adjusting the steering hydraulic system are located under the hood at the right side of the machine.

Test fitting (3) for the pump output pressure is located in the pump output line. Test fitting (20) for the signal pressure is located on the pump.

Pressure Settings for Piston Pump

When you check the pressures for the piston pump, several factors must be considered. Pump outlet pressure should remain approximately 2200 ± 100 kPa (320 ± 15 psi) higher than the maximum implement signal pressure. This difference in pressure is called the margin pressure.

When an implement stalls under a load, the piston pump should operate in a high pressure stall. When the piston pump is in a high pressure stall, the output pressure is at a maximum. When the machine is not being steered and all implement controls are in HOLD, the piston pump should operate in low pressure standby. The pump output pressure is at a minimum in low pressure standby.

Signal relief valve (5) and pressure and flow compensator valve (6) determine the output pressure of the pump against a load. If signal relief valve (5) is set below specifications, the high pressure stall will be low. A low pressure setting on the pressure compensator will also cause a low high pressure stall. The pressure compensator only functions as a backup to the signal relief valve and to the flow compensator. The pressure compensator should not be set to a lower pressure than the sum of the signal relief valve and the flow compensator. The setting for the signal relief valve must be checked after you adjust the high pressure stall.

Low Pressure Standby Test

1. Ensure that the hydraulic oil is warm. Refer to Systems Operation, "Machine Preparation for Troubleshooting" for further information.

2. Lower the boom and retract the boom. Ensure that the frame is level.

3. Stop the engine. Turn the steering wheel in both directions. This procedure helps purge pressure from the hydraulic system.

4. Connect Tooling (A) to test fitting (3) .

5. Start the engine and operate the engine at low idle. Do not turn the steering wheel and do not operate the implement controls. The output pressure for the piston pump at test fitting (3) should be approximately 2400 ± 400 kPa (350 ± 60 psi). This is the standby pressure for the piston pump. If the pressure is out of the specification, adjust the standby pressure. Refer to Testing and adjusting, "Low Pressure Standby Adjustment" for the proper procedure.

6. If the pressure is within the specification, stop the engine and remove Tooling (A) .

Signal Relief Valve Test

Note: Low pressure standby should be within specifications before this test is performed.

Note: The signal relief valve test and the high pressure stall test can be done at the same time.

1. Ensure that the hydraulic oil is warm. Refer to Systems Operation, "Machine Preparation for Troubleshooting" for further information.

2. Lower the boom and retract the boom. Ensure that the frame is level.

3. Stop the engine. Turn the steering wheel in both directions. This procedure helps purge pressure from the hydraulic system.

4. Connect Tooling (B) to test fitting (20) .

5. Start the engine and operate the engine at low idle. Operate the control for the boom retract until the pump reaches a stall condition. The pressure at test fitting (20) should be 22800 ± 500 kPa (3300 ± 75 psi). This is the signal relief pressure. If the signal relief valve is not within the specification, adjust the valve before you proceed with any other tests. Refer to , "Signal Relief Valve Adjustment".

6. If the pressure is within the specification, stop the engine and remove Tooling (B) .

Margin Pressure Test

Part of this test includes a check of the steering pressure. Refer to Testing and Adjusting, "Steering Pressure Test" for the proper steering system pressure. If the steering pressure is not within the specification, adjust the steering pressure. Refer to Testing and Adjusting, "Steering Pressure Adjustment".

1. Before you check margin pressure, ensure that the signal relief valve is adjusted correctly. Refer to Testing and Adjusting, "Signal Relief Valve Test". If the valve is adjusted correctly, proceed to the next step.

2. Ensure that the hydraulic oil is warm. Refer to Systems Operation, "Machine Preperation for Troubleshooting" for further information.

3. Lower the boom and retract the boom. Ensure that the frame is level.

4. Stop the engine. Turn the steering wheel in both directions. This procedure helps purge pressure from the hydraulic system.

5. Divide Tooling (B) into two separate gauge assemblies. Install a pressure gauge on test fitting (3) and install a pressure gauge on test fitting (4) .

6. Start the engine and operate the engine at low idle. Rotate the steering wheel for the full distance of travel. Subtract the pressure at test fitting (4) from the pressure at test fitting (3) . The difference in pressure should be 2200 ± 100 kPa (320 ± 14 psi). This is the margin pressure. If the pressure is out of the specification, test low pressure standby. Refer to Testing and Adjusting, "Low Pressure Standby Adjustment".

High Pressure Stall Test

Note: The high pressure stall test and the signal relief valve test can be done at the same time.

1. Ensure that the hydraulic oil is warm. Refer to Systems Operation, "Machine Preparation for Troubleshooting" for further information.

2. Lower the boom and retract the boom. Ensure that the frame is level.

3. Stop the engine. Turn the steering wheel in both directions. This procedure helps purge pressure from the hydraulic system.

4. Connect Tooling (B) to test fitting (3) .

5. Start the engine and operate the engine at low idle. Move the joystick control to BOOM RETRACT and hold the joystick control in this position in order to stall the pump. The output pressure for the pump at test fitting (3) should be 25000 ± 500 kPa (3626 ± 73 psi). This is the high pressure stall reading. If the pressure is not within the specification, an adjustment is necessary. Refer to Testing and Adjusting, "High Pressure Stall Adjustment".

6. If the pressure is within the specification, stop the engine and remove Tooling (B) .

Test for Pressure Compensator

The pressure compensator functions as a backup for controlling the high pressure stall. A test is not available for checking the pressure compensator due to the layout of this system. Ensure that all other pressures are within the specifications. A procedure for adjusting the pressure compensator is available. Refer to Testing and Adjusting, "Pressure Compensator Adjustment".

Steering Pressure Test

The steering system pressure and the margin pressure can be checked at the same time. Refer to Testing and Adjusting, " Margin Pressure Test".

1. Ensure that the hydraulic oil is warm. Refer to Systems Operation, "Machine Preparation for Troubleshooting" for further information.

2. Lower the boom and retract the boom. Ensure that the frame is level.

3. Stop the engine. Turn the steering wheel in both directions. This procedure helps purge pressure from the hydraulic system.

4. Connect Tooling (B) to test fitting (4) .

5. Start the engine and operate the engine at low idle. Raise the boom until the work tool is off of the ground. Rotate the steering wheel for the full distance of travel. Continue to rotate the steering wheel in order to check the steering pressure. The pressure should be 18500 ± 500 kPa (2685 ± 75 psi). The pressure reading will not be constant. Record the high side of the measured value. If the pressure is not within the specification, adjust the steering relief valve. Refer to Testing and Adjusting, "Steering Pressure Adjustment".

6. Straighten the steering wheel and lower the work tool to the ground.

7. If the pressure is within the specification, stop the engine and remove Tooling (B) .

Low Pressure Standby Adjustment

Illustration 4	g00743214
(7) Seal (8) Cap nut (9) Adjusting bolt (10) Locknut

Low pressure standby is controlled by the setting of the flow compensator spool.

Note: This adjustment may be performed while the engine is running.

1. Remove cap nut (8) and seal (7) . Loosen locknut (10) . Turn adjusting screw (9) clockwise in order to increase the standby setting. Turn the adjusting bolt counterclockwise in order to decrease the low pressure standby setting.

   Note: Do not turn the adjusting bolt more than a half turn at a time.

2. Hold adjusting screw (9) in place while you tighten locknut (10) .

3. Install seal (7) and cap nut (8) .

4. Recheck the pressure setting. Refer to Testing and Adjusting, "Low Pressure Standby Test".

Signal Relief Valve Adjustment

Use the following procedure to adjust the setting for the signal relief valve.

Note: This adjustment may be performed while the engine is running.

Illustration 5	g00743213
(11) Cap nut (12) Seal (13) Locknut (14) Adjusting bolt

1. Remove cap nut (11) and seal (12) .

2. Loosen locknut (13) . Turn adjusting screw (14) clockwise in order to increase the pressure setting or turn counterclockwise in order to decrease the pressure setting.

   Note: Do not turn the adjusting bolt more than a half turn at a time.

3. Hold adjusting screw (14) in place while you tighten locknut (13) .

4. Recheck the pressure setting. Refer to Testing and Adjusting, "Signal Relief Valve Test".

5. Install seal (12) and cap nut (11) .

Margin Pressure Adjustment

Margin pressure should be within specifications after all other adjustments are made. If the margin pressure is not within the specification, recheck low pressure standby. Refer to Testing and Adjusting, "Low Pressure Standby Test". If a problem still exists, a faulty resolver may be the problem. Refer to Testing and Adjusting, "Signal Resolver Network - Test".

Adjustment for High Pressure Stall

There is not a simple adjustment for the high pressure stall on this hydraulic system. This is due to the fact that the flow compensator and the signal relief valve control high pressure standby. On this hydraulic system, the pressure compensator serves as a backup.

1. Perform Step 2 through Step 5 of Margin Pressure Test.

2. Operate the control for the boom retract until the pump reaches a stall condition. The pressure at test fitting (4) should be 22910 kPa (3323 psi). Subtract the pressure at test fitting (4) from the pressure at test fitting (3) . This is the margin pressure. The margin pressure should be 2090 ± 100 kPa (300 ± 15 psi).

   1. If the pressure for the signal relief valve is incorrect at test fitting (4) and the margin pressure is correct, the signal relief valve needs to be adjusted. Refer to Testing and Adjusting, "Signal Relief Valve Adjustment".

   2. If the margin pressure was correct and the pressure for the signal relief valve was correct , check the pressure at test fitting (3) . The pressure should be 25000 ± 500 kPa (3626 ± 73 psi). This is the high pressure stall reading.

   3. If the high pressure stall reading is low, the pressure compensator needs to be adjusted. Refer to Testing and Adjusting, "Pressure Compensator Adjustment". If the pressure at test fitting (3) was identical to the signal pressure at test fitting (4) , the pressure compensator needs to be adjusted. Refer to Testing and Adjusting, "Pressure Compensator Adjustment".

Adjustment for Pressure Compensator Spool

Illustration 6	g00743215
(15) Seal (16) Cap nut (17) Adjusting bolt (18) Locknut

1. Check the margin pressure and adjust, if necessary. Refer to Testing and Adjusting, "Margin Pressure Test". Do not remove Tooling (B) . Operate the engine at low idle.

2. Remove cap nut (16) and seal (15) .

3. Loosen locknut (18) .

4. Turn adjusting screw (17) counterclockwise in order to reduce the setting of the pressure compensator. Turn the screw until the margin pressure begins to drop.

5. When the margin pressure begins to drop, turn adjusting screw (17) clockwise by a 1/4 turn. This ensures that the pressure compensator is set above the adjustment for the signal relief valve.

6. Tighten locknut (18) while you hold screw (17) in place.

7. Install seal (15) and cap nut (16) .

8. Stop the engine and remove Tooling (B) from the machine.

Steering Pressure Adjustment

The steering pressure can be adjusted at the metering pump (steering).

Note: This adjustment can be made with the engine running.

Illustration 7	g00743236
Location of Metering Pump (Steering)

Remove the cover from the front of the cab in order to gain access to the metering pump.

Illustration 8	g00743217
Steering Signal Relief Valve (19) Plug (20) Adjusting bolt

1. Remove plug (19) .

2. Use an appropriate sized hex key wrench to turn adjusting screw (20) . Turn the screw clockwise in order to increase the pressure setting. Turn the screw counterclockwise in order to lower the pressure setting.

   Note: Do not turn the adjusting bolt more than a half turn at a time.

3. Recheck the pressure setting. Refer to Testing and Adjusting, "Steering Pressure Test".

4. Install plug (19) .