980G Wheel Loader Braking System Caterpillar

Show/hide table

Personal injury or death can result if two persons are not used in the following procedure.

Show/hide table

Escaping fluid under pressure, even a pinhole 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. Always use a board or cardboard when checking for a leak.

Complete the procedure in the Service Manual module Testing and Adjusting, "Machine Preparation for Troubleshooting" prior to testing the machine.

"Procedure 1" is a quick method for checking the cutout pressure. This procedure also indicates whether the oil pressure switch for the service brakes and the brake oil pressure indicator operate correctly. The procedure provides an estimate of the accumulator precharge pressure and an estimate of the number of brake applications before the brake oil pressure indicator turns on.

"Procedure 2" determines whether the cut-in pressure and the cutout pressure are correct. This procedure also provides the required steps for adjusting the brake accumulator charging valve.

Procedure 1

1. Stop the engine. Engage the parking brake. Depress the brake pedal repeatedly until there is no brake oil pressure.

Note: The operator's cab and the platform have been removed for clarity in the following illustration.

Show/hide table



Illustration 1	g00476364
Location of the Pressure Port for the Brake Accumulator Charging Valve (1) Accumulator charging valve. (2) Test port.

Note: The brake accumulator charging valve is located on the right side of the machine under the operator's platform.

2. Connect a 0 to 20700 kPa (0 to 3000 psi) pressure gauge at test port (2) on brake accumulator charging valve (1) .

3. Observe the pressure gauge. Before you start the engine, the oil pressure must be 0 kPa (0 psi).

4. Start the engine. Allow the oil pressure to increase to the cutout pressure. The correct cutout pressure should be 14485 ± 345 kPa (2100 ± 50 psi).

5. After the brake accumulators have been completely charged and the correct cutout pressure has been obtained, stop the engine.

6. Turn the engine key start switch to the ON position, but do not start the engine.

7. Apply the service brakes repeatedly. Pause for two seconds before each brake application and count the number of applications while you observe the pressure gauge.

Show/hide table



Illustration 2	g00476366
Instrument Panel (3) Brake oil pressure indicator.

8. When the reading on the pressure gauge decreases to 8960 ± 345 kPa (1300 ± 50 psi), brake oil pressure indicator (3) will turn ON. This indicates the operational status of brake oil pressure indicator (3). This also indicates the operational status of the brake oil pressure switch for the service brakes. The brake oil pressure switch is located beside accumulator charging valve (1). The brake accumulator charging valve is located on the right side of the machine under the operator's platform.

9. Continue to apply the service brakes, pausing for a second or two before each brake application. When the pressure drops off rapidly, this indicates the approximate nitrogen precharge pressure in the brake accumulators.

10. Determine the number of brake applications that were required before the sudden pressure drop in Step 9. This number should be more than five times.

11. If the cutout pressure is not within the specification, complete Steps 7 through 12 in "Procedure 2". If the nitrogen precharge pressure is not within the specification, see the following reference.

    ReferenceFor additional information on charging the brake accumulators, refer to the Service Manual for Testing and Adjusting, "Brake Accumulator - Test and Charge".

Procedure 2

Note: Use the same operational conditions that were used in "Procedure 1". Use the same precautions that were used in "Procedure 1".

1. Stop the engine. Engage the parking brake. Depress the brake pedal repeatedly until there is no brake oil pressure.

Note: The operator's cab and the platform have been removed for clarity in the following illustration.

Show/hide table



Illustration 3	g00476364
Location of the Pressure Port for the Brake Accumulator Charging Valve (1) Accumulator charging valve. (2) Test port.

2. Connect a 0 to 20700 kPa (0 to 3000 psi) pressure gauge at test port (2) on brake accumulator charging valve (1) .

3. Observe the pressure gauge. Before you start the engine, the oil pressure must be 0 kPa (0 psi).

4. Start the engine and immediately raise the engine speed to high idle.

5. The oil pressure must increase to maximum pressure. Record this pressure. This is the cutout pressure of the brake accumulator charging valve. The correct cutout pressure should be 14485 ± 345 kPa (2100 ± 50 psi).

6. With the engine in operation, slowly apply the service brakes. Apply the service brakes several times in succession. Verify that the pressure drops consistently. At the point of the specified cut-in, the pressure begins to increase quickly. The cut-in pressure should be 11725 ± 345 kPa (1700 ± 50 psi).

7. If the cut-in pressure and the cutout pressure are not within the specification, stop the engine and completely release all oil pressure from the brake circuit by depressing the brake pedal repeatedly. Loosen the hydraulic tank filler cap in order to make sure that there is no residual pressure in the hydraulic oil tank.

Show/hide table



Illustration 4	g01159925
Accumulator Charging Valve (3) Inlet from the brake pump. (4) Adjustment screw underneath the hex plug. (5) Accumulator port for the front service brakes. (6) Outlet to the hydraulic oil tank. (7) Port for the oil pressure switch for the service brakes. (8) Accumulator port for the rear service brakes. (9) Pressure relief valve. (10) Access to the main check valve.

Show/hide table



Illustration 5	g01159927
Accumulator Charging Valve (4) Adjustment screw underneath the hex plug. (10) Access to the main check valve.

8. Remove the hex plug that covers adjustment screw (4) .

   Note: The charging limits will move together. The range between cut-in pressure and the cutout pressure is not adjustable.

9. Turn adjustment screw (4) by a quarter turn. Turning the adjustment screw clockwise will increase the cut-in pressure and the cutout pressure. Turning the adjustment screw counterclockwise will decrease the cut-in pressure and the cutout pressure.

10. Install the hex plug that covers adjustment screw (4), and tighten the hydraulic tank filler cap.

11. Start the engine. Make sure that the cut-in pressure and the cutout pressure are within the specification. If the pressures are not within the specification, repeat Steps 7 through 11.

12. If the cut-in pressure and the cutout pressure are not within the specification, the brake accumulator charging valve may need to be repaired or replaced.