Troubleshooting

During a diagnosis of the hydraulic system, remember that correct oil flow and pressure are necessary for correct operation. The output of the pump (oil flow) increases with an increase in engine speed (rpm) and decreases when engine speed (rpm) is decreased. Oil pressure is caused by resistance to the flow of oil.

The 4C4890 Fittings Group can be used to make pressure tests on the secondary/parking brake system. Before any tests are made, visually inspect the complete hydraulic system for leakage of oil and for parts that are damaged. For some of the tests a magnet and a mm (in) measuring rule are usable tools.

When any test is made of the secondary/parking brake system, the hydraulic oil must be at the normal temperature for operation.

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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, do the procedure that follows before testing and adjusting the secondary/parking brake system.

1. Move the machine to a smooth horizontal location. Move away from working machines and personnel.

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

3. Activate the parking brake.

4. Stop the engine.

5. Move the hydraulic control lever to all positions to release any pressure in the hydraulic system.

6. Carefully loosen the filler cap on the hydraulic tank to release any pressure in the tank.

7. Make sure all hydraulic pressure is released before any fitting, hose or component is loosened, tightened, removed or adjusted.

8. Tighten the filler cap on the hydraulic tank.

9. The pressure in the system has now been released and the lines or components can be removed.

Visual Checks

A visual inspection of the secondary/parking brake system and its components is the first step when a diagnosis of a problem is made. Then check the operation of the machine. Finally, check the secondary/parking brake system with instruments. Stop the engine, make the following inspections.

1. Check the oil level of the hydraulic tank.

2. Look for air in the oil that is in the tank. Do this immediately after the machine is stopped. Use a clear bottle or container to get a sample of the oil. Look for air bubbles in the oil that is in the bottle.

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Do not check for leaks with your hands. Pin hole (very small) leaks can result in a high velocity oil stream that will be invisible close to the hose. This oil can penetrate the skin and cause personal injury. Use cardboard or paper to locate pin hole leaks.

3. Check all oil lines, hoses and connections for leaks and damage. Look for oil on the ground under the machine.

4. Remove and check the hydraulic filter element for foreign materials.

a. Bronze-colored particles give an indication of pump port plate failure.

b. Shiny steel particles give an indication of pump or motor piston failure or motor cam deterioration.

c. Rubber particles give an indication of a seal or hose failure.

d. Aluminum particles give an indication of steering pump failure.

5. Inspect electrical wiring for broken connections or damaged components.

Brake Operation Check

Perform the following steps to learn whether the secondary/parking brake is operating properly. Do this check on a dry, level, compacted surface. Clear the area in the direction of machine travel.

1. Start the engine following proper operating procedures.

2. Set the speed range shift switch in LOW position.

3. Push the brake switch button down to apply the secondary/parking brake. The lamp located in the brake switch should light.

4. Set the throttle control lever at approximately half throttle.

5. Move the propel lever slightly forward. The engine should stall noticeably (or rear wheels spin) and the machine should hold its position.

6. Move the propel lever back to the center/stop position.

7. Move the throttle control lever to the full throttle position.

8. Pull the brake switch button up to release the secondary/parking brake. The brake switch lamp should go out.

9. Move the propel lever slightly forward. The machine should move forward as soon as the propel lever is moved.

10. Move the propel lever back to the center/stop position. Stop the engine. Push the brake switch button down to apply the secondary/parking brake.

11. If the machine moves forward with the secondary/parking brake applied in Step 5, preform the Brake Pressure Test in this module.

12. If the secondary/parking brake holds the machine in Step 5 but the brake switch lamp does not light, replace the bulb in the brake switch.

13. If the machine does not move forward in Step 9, the secondary/parking brake is not releasing properly. Perform the Brake Pressure Test in this module.

Problem: Brake does not hold machine.

Probable Cause:

This problem could be caused by an electrical or hydraulic problem, allowing oil to be routed to the front gear reduer, when the brake should be applied. Worn or damaged components in the front gear reducer could also reduce the efficiency of the brake.

1. Check the hydraulic oil leakage through the brake solenoid valve.

2. Check the brake switch for damage, and replace if necessary.

3. Check the brake interlock valve for damage, and replace if necessary.

4. Check for shorts in the electrical wiring to the brake solenoid valve.

5. Check the brake components in the front gear reducer for damage or excessive wear, and replace parts as necessary.

Problem: Brake will not release.

Probable Cause:

This could be caused by a lack of hydraulic pressure available to release the brake. Electrical components or wiring may be damaged, preventing the controls from working. Worn or damaged components in the front gear reducer can also prevent the brake from releasing.

1. Perform the Brake Pressure Test in this module.

2. Check the pressure switch and the brake switch for damage, and replace if necessary.

3. Check the brake solenoid valve for damage.

4. Check for shorts in the electrical wiring to the brake solenoid valve.

5. Check the brake components in the front gear reducer for damage or excessive wear, and replace as necessary.

Problem: Brake pressure too low.

Probable Cause:

Low system pressure is likely caused by leakage in the brake system, or by insufficient pressure from the steer system.

1. Check the brake solenoid valve for internal leakage.

2. Perform the Front Gear Reducer Pressure Test to check the front gear reducer for leakage.

3. Examine the check valve and the steer pump (both part of the steer system) for correct operation.

NOTE: For information on the check valve and steer pump, see Steering Systems Operation Testing And Adjusting, Form No. KEBR2249.

Problem: Brake light stays on or flickers during operation.

Probable Cause:

This could be caused by low hydraulic pressure, a faulty pressure switch or a faulty brake switch.

1. Perform the Brake Pressure Test in this module.

2. Perform the Pressure Switch Continuity Test in this module.

3. Check the brake switch for damage, and replace if necessary.

Brake Pressure Test

Test Port Location
(1) Test port X4.

1. Remove the cap from test port X4 (1) behind the operator's seat. Connect a 25 000 kPa (3600 psi) pressure gauge to test port X4 (1).

2. Start the engine and run at full throttle.

3. Push the brake switch button down to apply the brake. The lamp located in the brake switch should light.

4. Observe and record the pressure gauge reading. The pressure reading should be zero.

5. Pull the brake switch button up to release the brake. The brake switch lamp should go out.

NOTE: Do not turn the steering wheel in the following step. Turning the steering wheel will increase brake pressure to approximately 13 750 kPa (2000 psi). This would cause incorrect test results.

6. Observe and record the pressure gauge reading. The pressure reading should be a minimum of 3100 kPa (450 psi).

7. Stop the engine. Push the brake switch button down to apply the brake. Pressure should go to zero. Remove the pressure gauge from test port X4 (1) and replace the cap.

8. If the pressure reading in Step 4 is greater than zero, the brake solenoid valve is not operating properly. Perform the Brake Solenoid Valve Electrical Test in this module.

9. If the pressure reading in Step 4 is zero, but the brake will not hold the machine, there is probably an internal brake problem. Brake components in the front gear reducer may need to be replaced.

10. If the pressure reading in Step 6 is zero, the brake solenoid valve is not operating properly. Perform the Brake Solenoid Valve Electrical Test in this module.

11. If the pressure gauge in Step 6 records some pressure other than 3100 kPa (450 psi), perform the Front Gear Reducer Pressure Test in this module.

12. If the pressure reading in Step 6 is correct, but the brake will not release, there is probably an internal brake problem. Brake components in the front gear reducer may need to be replaced.

Front Gear Reducer Pressure Test

Perform this test if the hydraulic pressure measured in Step 6 of the Brake Pressure Test is too low to release the brake. This test will tell you whether the problem is in the front gear reducer, or in another part of the system.

Front Gear Reducer
(1) Hydraulic hose. (2) Brake port.

1. Disconnect hydraulic hose (1) from brake port (2) of the front gear reducer. Plug brake port (2) to prevent contaminants from entering.

2. nonnect a 25 000 kPa (3600 psi) pressure gauge to hydraulic hose (1).

3. Start the engine and run at full throttle.

4. Pull the brake switch button up to release the brake.

5. Observe and record the pressure gauge reading.

6. Stop the engine. Push the brake switch button down to apply the brake.

7. Remove the pressure gauge, and connect hydraulic hose (1) to brake port (2).

8. If the pressure reading in Step 5 is at least 3100 kPa (450 psi), the low pressure reading in the Brake Pressure Test is due to a problem in the front gear reducer. Brake components in the front gear reducer may need to be replaced.

9. If the pressure reading in Step 5 is less than 3100 kPa (450 psi), the low pressure reading in the Brake Pressure Test is not caused by the front gear reducer. Refer to the Troubleshooting section of this module for a probable cause.

Brake Solenoid Valve Electrical Test

If moving the brake switch button does not apply or release the brake correctly, check the electrical wiring to the brake solenoid valve as follows.

Brake Solenoid Valve
(1) Wire. (2) Ground screw. (3) Wire. (4) Coil.

Instrument Panel
(5) Engine start switch. (6) Ten amp fuse.

1. Check ten amp fuse (6) on the instrument panel, and replace if necessary.

2. Set the multimeter on the lowest resistance scale.

3. With engine start switch (5) in the OFF position, touch the leads of the multimeter to wires (1) and (3). Electrical resistance should be 8 ohms. If not, replace coil (4).

4. Make sure wire (1) is connected to ground screw (2). Secure ground connection if necessary.

5. Start the engine and run at full throttle.

6. Set the multimeter on the 20 DC volt scale.

7. Push the brake switch button down to apply the brake. Touch the leads of the multimeter to wires (1) and (3). The voltage reading on the multimeter should be zero.

8. Pull the brake switch button up to release the brake. The voltage reading on the multimeter should be approximately 12 volts.

9. Stop the engine. Push the brake switch button down to apply the brake. Disconnect the multimeter from the wires.

10. If the voltage reading in Step 7 is not zero, the brake switch should be checked, and replaced if necessary.

11. If the voltage reading in Step 8 is not 12 volts, perform the Pressure Switch Continuity Test in this module. If the electrical resistance of the pressure switch is correct, check whether 12 volts is available at the brake switch.

12. If 12 volts is available at the brake switch but not at the brake solenoid valve, the brake switch may be damaged, or the wiring between the brake switch and the brake solenoid valve may be faulty.

13. If 12 volts is not available at the brake switch, check the wiring from the brake switch to the alternator. Repair or replace any faulty wiring or component.

Pressure Switch Continuity Test

Pressure Switch
(1) COM (Common) terminal. (2) NO (Normally open) terminal. (3) NC (Normally closed) terminal.

1. Disconnect the three wires from terminal (1), terminal (2) and terminal (3) of the pressure switch. Mark the three wires for reassembly.

2. Set the multimeter on the lowest resistance scale.

3. With the engine OFF, touch the leads of the multimeter to terminal (1) and terminal (3). The electrical resistance should be zero ohms.

4. Set the multimeter on its highest resistance scale.

5. Touch the leads of the multimeter to terminal (1) and terminal (2). Electrical resistance should be infinite.

6. If the electrical resistance in Steps 2 and Step 4 is not correct, the pressure switch must be replaced.

7. Start the engine and run at full throttle.

8. Touch the leads of the multimeter to terminal (1) and terminal (2). Electrical resistance should be zero ohms.

9. Touch the leads of the multimeter to terminal (1) and terminal (3). The electrical resistance should be infinite (OL).

10. If electrical resistance in Step 7 and Step 8 is not correct, perform the Brake Pressure Test in this module. If the brake system pressure is correct, the pressure switch must be replaced. If the brake system pressure is not correct, refer to the Troubleshooting section in this module for a probable cause.