938G Series II Wheel Loader and IT38G Series II Integrated Toolcarrier Braking System Accumulator Charging Valve (Brake) - Test and Adjust Caterpillar


Accumulator Charging Valve (Brake) - Test and Adjust
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1.1. Procedure To Disconnect Power To The Secondary Steering Motor
2.1. Procedure 1
3.1. Procedure 2

Table 1
Required Tools    
Part Number     Description     Qty    
1U-5481     Pressure Gauge Group     1    

------ WARNING! ------

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

----------------------


NOTICE

Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids.

Refer to Special Publication, NENG2500, "AVSpare Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on AVSpare products.

Dispose of all fluids according to local regulations and mandates.


Note: There are two separate procedures that may be used to check the operation of the brake accumulator charging valve and the operation of several associated components. Both procedures should be used.

"Procedure 1" is a quick method for checking the cutout pressure. This procedure also indicates whether the service brake oil pressure switch 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.


NOTICE

If the machine is equipped with secondary steering, the power for the secondary steering motor must be temporarily disconnected.

Failure to disconnect power to the secondary steering motor before performing Procedure 1 and Procedure 2 may cause the secondary steering motor to fail prematurely.

Use the following procedure to disconnect power to the secondary steering motor.


Procedure To Disconnect Power To The Secondary Steering Motor




    Illustration 1g00279597

    (1) Tilt hood actuator switch.

  1. Tilt hood actuator switch (1) is located on the right rear side of the machine. Raise the access cover for the switch. To raise the engine hood, pull up on the switch handle and then push the switch handle to one side.



    Illustration 2g00280017

    Disconnect Switch

  1. Insert the key for disconnect switch (2) . Turn the key counterclockwise in order to disconnect power for the machine.

  1. Remove the key from the disconnect switch. Place a "DO NOT OPERATE" tag on the disconnect switch.



    Illustration 3g00280037

    (3) Terminal. (4) Wire.

  1. Carefully slide the rubber boot off terminal (3) . Use a 19.0 mm (0.75 inch) wrench to remove the nut that secures wire (4) to terminal (3) .

  1. Wrap electrical tape around the exposed end of wire (4) . Install the nut that was removed in Step 4, but do not tighten the nut.

  1. Insert the key for disconnect switch (2) . Turn the key clockwise in order to connect power for the machine.

  1. Remove the "DO NOT OPERATE" tag.

Procedure 1

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



    Illustration 4g00279590

    Brake Components

    (1) Test port. (2) Accumulator for the rear service brakes. (3) Accumulator for the front service brakes. (4) Accumulator charging valve.

    Note: The cab has been removed for photographic clarity only.

  1. Connect a 0 to 40000 kPa (0 to 5800 psi) pressure gauge to test port (1) on brake accumulator charging valve (4) .

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

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

    Note: The correct cut-in pressure is 11725 ± 345 kPa (1700 ± 50 psi).

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

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

  1. Apply the service brakes repeatedly. Pause for two seconds between brake applications. Count the number of applications while you observe the pressure gauge.



    Illustration 5g00934865

    (5) Brake oil pressure indicator.




    Illustration 6g00280033

    (6) Service brake oil pressure switch. (7) Accumulator charging valve.

  1. When the reading on the pressure gauge decreases to 8960 ± 345 kPa (1300 ± 50 psi), brake oil pressure indicator (5) will turn on. This indicates the operational status of the indicator and of service brake oil pressure switch (6) . Service brake oil pressure switch (6) is located next to accumulator charging valve (7) . The accumulator charging valve is located on the left side of the machine beneath the cab platform.

  1. Continue to apply the service brakes and pause for two seconds between brake applications. When the pressure drops off rapidly, this indicates the approximate nitrogen precharge pressure in the brake accumulators.

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

  1. If the cutout pressure is not within the specification, complete Steps 7 through 11 in "Procedure 2". If the nitrogen precharge pressure is not within the specification, refer to Testing and Adjusting, "Brake Accumulator - Test and Charge".

Procedure 2

Note: The same operating conditions and the same precautions as "Procedure 1" should be followed. This includes disconnecting power to the secondary steering motor if the machine is equipped with secondary steering.

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



    Illustration 7g00279590

    Brake Components

    (1) Test port. (2) Accumulator for the rear service brakes. (3) Accumulator for the front service brakes. (4) Accumulator charging valve.

    Note: The cab has been removed for photographic clarity only.

  1. Connect a 0 to 40000 kPa (0 to 5800 psi) pressure gauge to test port (1) on brake accumulator charging valve (4) .

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

  1. Start the engine and immediately raise the engine rpm to high idle. Watch for a pause in the increase of oil pressure. Record the reading on the pressure gauge when this occurs. This is the approximate nitrogen precharge pressure in the brake accumulators. If the nitrogen precharge pressure is not within the specification, refer to Testing and Adjusting, "Brake Accumulator - Test and Charge".

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

    Note: The correct cut-in pressure is 11725 ± 345 kPa (1700 ± 50 psi).

  1. Apply the service brakes repeatedly while the engine is running. Verify a consistent pressure drop. At the point of the specified cut-in, the pressure begins to increase quickly.

  1. 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.



    Illustration 8g00280036

    Accumulator Charging Valve

    (5) Cover for the adjustment screw. (6) Relief valve. (7) Port for the brake oil pressure switch. (8) Accumulator port for the rear brakes. (9) Outlet to the hydraulic oil tank. (10) Accumulator port for the front brakes. (11) Plug. (12) Inlet from the brake pump.

    Note: Machines that are equipped with the traction control system use a 135-4391 Accumulator Charging Valve . Both of the accumulator valves are similar.

  1. Remove the cover for adjustment screw (5) .

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

  1. Turn the hex plug under cover (5) by 1/4 turn. Turning the hex plug clockwise will increase the cut-in pressure and the cutout pressure. Turning the hex plug counterclockwise will decrease the cut-in pressure and the cutout pressure.

  1. Install cover (5) and tighten the hydraulic tank filler cap.

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

    If the cut-in pressure and the cutout pressure cannot be adjusted within the specifications, replace the brake accumulator charging valve.

  1. Refer to Step 4 in the "Procedure To Disconnect Power To The Secondary Steering Motor". Attach wire (4) onto terminal (3) .

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