770 and 772 Off-Highway Truck Hydraulic and Braking System Brake System Air - Purge Caterpillar


Brake System Air - Purge
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1.1. Service Brakes and Retarder
2.2. Rear Brakes
3.2. Front Brakes

Table 1
Required Tools    
Part Number     Description     Required Amount    
6V-4144     Quick Connect Coupler     1    
235-7104     Hose As     2    
1S-8937     Needle Valve     1    

There are quick disconnects for the hydraulic brakes on each rear wheel. Before you purge air from the oil in the system, the brake system accumulators must be fully charged.

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

Personal injury or death can result from air in the oil for the brake hydraulic system.

Air in the system can prevent complete brake application and it is possible that the wheels on the machine can not be stopped.

Air must not be in the oil for the brake hydraulic system to function properly.

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

Personal injury or death can result from machine movement.

Place blocks in front of and behind the wheels to make sure the machine does not move while the parking brakes are disengaged.

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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: Purge only one wheel at a time.

Service Brakes and Retarder

Rear Brakes

  1. Assemble the following in order to construct a purge hose assembly: one 6V-4144 Coupler, two 235-7104 Hose As, and one 1S-8937 Needle Valve



    Illustration 1g01334583

    Purge hose assembly

    (1) Hose Assembly

    (2) Quick Connect Coupler

    (3) Needle Valve




    Illustration 2g01332716

    (1) Hose Assembly

    (2) Quick Connect Coupler

    (4) Quick disconnect for the right rear brake

  1. Connect the 6V-4144 Quick Connect Coupler (2) to the quick disconnect fitting (4) on the rear brakes.



    Illustration 3g01332737

    Note: In order to make sure that the brake accumulators are fully charged, operate the engine at high idle for 20 seconds before each brake application.

  1. Remove the cap from the hydraulic oil tank (5) and insert the other end of the purge hose assembly (1) into the filler neck.

  1. Run the engine at low idle.

  1. Open the 1S-8937 Needle Valve (3). This will allow oil to flow to the hydraulic tank.

  1. Depress the service brake pedal. Hold the brake pedal for approximately 20 seconds. This will purge the air from the hydraulic brake oil.

  1. Close the 1S-8937 Needle Valve (3) .

  1. Release the service brake pedal.

  1. Disconnect the 6V-4144 Quick Connect Coupler (2) from the quick disconnect fitting (4) on the rear brakes.

  1. Repeat Steps 2 through 9 for the other rear wheel brake.

Front Brakes

Note: In order to make sure that the brake accumulators are fully charged, operate the engine at high idle for 20 seconds before each brake application.

  1. Depress the service brake pedal. Run the engine at low idle.



    Illustration 4g01333147

    View of front service brake caliper (if equipped)

    (6) Purge valve

  1. Connect a drain hose from purge valve (6) to the hydraulic tank or to a suitable container.

  1. Open purge valve (6) on a front wheel brake housing and purge the brake system.

  1. Repeat Steps 1 through 3 until there is a continuous flow of oil.

  1. Close the purge valve. Release the brake pedal.

  1. Complete Steps 1 through 5 on the other front wheel brake.

  1. Remove the drain hose.

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