776D, 777D and 777D HAA Off-Highway Truck/Tractors Air System and Brakes Service Brakes and Retarder System Pressure - Test Caterpillar

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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.

Note: Remove air pressure from the air system for the service brake and for the retarder brake system before you remove the plugs from the air/hydraulic cylinders.

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Personal injury or death can result from sudden machine movement. Sudden movement of the machine or release of air pressure or oil pressure can cause injury to persons on or near the machine. To help prevent possible injury before testing and adjusting any air system or hydraulic system, perform the procedure in the Testing and Adjusting, "General Information" section.

1. Move the parking brake control to the ON position.

2. Remove all of the air pressure from the air circuit for the service brakes and the retarder brakes.

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Illustration 1	g00916330
Top view (1) Plug on the front air/hydraulic cylinder (2) Plug on the rear air/hydraulic cylinder (A) Hydraulic tank

3. Remove plug (1) from the top of the front air/hydraulic cylinder. Remove plug (2) from the top of the rear air/hydraulic cylinder.

4. Use a coupler and a hose to connect a 8T-0854 Pressure Gauge (0 to 1000 kPa (0 to 145 psi)) in the location of the plugs (1) and (2) .

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Illustration 2	g00647105
(3) Pressure tap for rear slack adjuster

5. Install a 8T-0857 Pressure Gauge (0 to 10000 kPa (0 to 1450 psi)) to pressure tap (3) on the rear brake slack adjuster.

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Illustration 3	g00732337
(4) Tee

6. Oil is sent from the air/hydraulic cylinder to a tee (4). Oil flow from tee (4) to the front caliper brakes. In order to check the pressure of the oil to the front caliper brakes, disconnect the hose that supplies oil to tee (4). Tee (4) is located behind the left front wheel on the frame rail. Install a 7X-0871 Tee in the line at tee (4). Install a 6V-3965 Nipple in the 7X-0871 Tee. Use a coupler and a hose to connect a 8T-0860 Pressure Gauge (0 to 40000 kPa (0 to 5800 psi)) to the nipple.

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Illustration 4	g00732336
(5) Pressure tap for front slack adjuster

7. Install a 8T-0857 Pressure Gauge (0 to 10000 kPa (0 to 1450 psi)) to pressure tap (5) on the front brake slack adjuster, if equipped.

8. Start the engine. Operate the engine at high idle.

9. Move the retarder control lever to the full ON position. The following pressures should be indicated:
   • Oil pressure at the rear slack adjuster should be a maximum of 3640 kPa (528 psi).

   • Oil pressure at the front slack adjuster (if equipped) should be a maximum of 6509 kPa (944 psi).

   • Oil pressure to the front caliper brakes should be 0 kPa (0 psi).

   • Air pressure at the rear air/hydraulic cylinder should be 550 kPa (80 psi).

   • Air pressure at the front air/hydraulic cylinder should be 0 kPa (0 psi).

   • Air pressure at the front air/hydraulic cylinder with oil cooled brakes should be 550 kPa (80 psi).

10. Move the retarder control lever to the OFF position. Apply the service brake. The following pressures should be indicated:
    • Oil pressure at the rear slack adjuster should be 4345 to 5445 kPa (630 to 790 psi).

    • Oil pressure at the front slack adjuster (if equipped) should be 7722 to 9756 kPa (1120 to 1415 psi).

    • Oil pressure to the front caliper brakes should be 19822 kPa (2875 psi).

    • Air pressure at the rear air/hydraulic cylinder should be 655 to 827 kPa (95 to 120 psi).

    • Air pressure at the front air/hydraulic cylinder should be 655 to 827 kPa (95 to 120 psi).

11. Stop the engine.

Note: Remove air pressure from the air system for the service brake and for the retarder brake system before you remove the couplers from the air/hydraulic cylinders.

12. Remove the tee, the gauges and the couplers. Install plug (1) and (2) into the elbows on the top of the air/hydraulic cylinders.

Note: Perform the Air System and Brakes Systems Operation/Testing and Adjusting, "Slack Adjuster - Test and Adjust" in order to determine the pressure at each rear wheel.

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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.

Note: Make sure that you remove all air from the hydraulic brake system. See the Testing and Adjusting, "Brake System Air - Purge" for the procedure.