STARTER GP 2389314 - Caterpillar

Illustration 1 g01198495
Rear air/hydraulic cylinders
Illustration 2 g00290367
Components for air/hydraulic 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 screw
(10) Passage
(11) Port for makeup oil
(12) Spring There are two rear air/hydraulic cylinders. The air/hydraulic cylinders are used for the standard application of the brakes. The same air/hydraulic cylinders are used for extended braking. All of the air/hydraulic 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 air/hydraulic 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 screw (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 on the message center of the Vital Information Management System (VIMS) illuminates and the action light on the dashboard illuminates. The warning horn will also sound. This condition can result from an oil leak that is located downstream from the air/hydraulic 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.