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| Illustration 1 | g00337194 |
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Front brake master cylinder | |
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| Illustration 2 | g00337196 |
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Rear brake master cylinders | |
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| Illustration 3 | g00290367 |
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Components for brake master cylinder (1) Air chamber (2) Piston (3) Rod (4) Overstroke pin (5) Overstroke switch (6) Valve (7) Power piston (8) Port for oil to brake pistons (9) Purge orifice (10) Passage (11) Port for makeup oil (12) Spring | |
The brake air/hydraulic cylinders (brake master cylinders) are a main component of the braking system. There are two rear brake master cylinders and one front brake master cylinder. The tractor has an additional two brake master cylinders on the rear of the machine for the pulled unit wheel brakes. All brake master cylinders are used for the standard application of the brakes. The same brake master cylinders are used for extended braking. All of the brake master cylinders operate the same way.
When the brake pedal is used or when the retarder is used, the brake air relay valve delivers air to air chamber (1). The pressurized air pushes piston (2) and rod (3). This compresses spring (12). Rod (3) moves valve (6) in order to close passage (10). As power piston (7) moves down, oil in the brake master cylinder flows out of port (8) to the slack adjusters. The oil moves the pistons in the slack adjusters.
When you stop applying the brakes, the brake air relay valve will prevent air from entering air chamber (1). In the absence of the air pressure, spring (12) pushes up piston (2) and rod (3). As rod (3) moves up, valve (6) will also move up. This opens passage (10). Valve (6) and power piston (7) will move up.
Any air that is below power piston (7) flows through passage (10) and through port (11) to the makeup oil tank. If any oil is needed below power piston (7), oil from the makeup oil tank flows through port (11). This oil flows around valve (6) and through passage (10). This prevents a vacuum lock below power piston (7).
Purge orifice (9) is not needed in this application.
Note: The brake oil pressure is approximately 6.6 times the amount of air pressure.
Overstroke switch (5) actuates when piston (2) moves beyond 75 percent of full travel. In this situation, piston (2) makes contact with overstroke pin (4). This causes overstroke switch (5) to open. When overstroke switch (5) opens, the alert indicator of the Vital Information Management System (VIMS) will illuminate. The action light on the dashboard will also illuminate. The warning horn will also sound. When overstroke switch (5) opens on machines that are equipped with the Electronic Monitoring System (EMS) the brake light will illuminate. The action light will also illuminate. The action alarm will also sound. This condition can result from an oil leak that is located downstream from the brake master cylinders. This condition also occurs if there is a problem with valve (6). Overstroke pin (4) must be manually reset. In order to reset overstroke switch (5), push overstroke pin (4) upward into the housing. The bottom of overstroke pin (4) should be flush with the bottom of the housing.