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| Illustration 1 | g00531836 |
Location of parking and secondary brake valve | |
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| Illustration 2 | g00277905 |
Parking and secondary brake valve in the ON position (1) Passage from brake pump section (2) Relief valve (4) Piston (5) Air inlet passage (6) Stem (7) Drain passage to the front brake cooling circuit (8) Drain passage to hydraulic tank (9) Check valve (10) Spring (11) Outlet passage for the oil that releases parking brakes | |
The parking and secondary brake valve is located on the left side of the truck frame near the fuel tank. The parking and secondary brake valve controls the flow of oil to the parking brakes for the rear wheels.
The spring applied parking brakes are released by hydraulic pressure. The engine must be in operation in order to have oil pressure in passage (1) from the parking brake release pump section.
The parking brake air control valve and the secondary brake air control valve are located in the cab. When either of these controls are in the ON position, air flow to air inlet passage (5) will be stopped. When there is no air flow to air inlet passage (5), spring (10) will keep stem (6) in place. This blocks the flow of oil from passage (1) to passage (11). When no oil flows to the parking brakes for the rear wheels, a spring will apply the parking brakes for the rear wheels.
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| Illustration 3 | g00277906 |
Parking and secondary brake valve in the OFF position (1) Passage from brake pump section (2) Relief valve (4) Piston (5) Air inlet passage (6) Stem (7) Drain passage to the front brake cooling circuit (8) Drain passage to hydraulic tank (9) Check valve (10) Spring (11) Outlet passage for the oil that releases parking brakes | |
The parking brake air control valve and the secondary brake air control valve are located in the cab. When both of these controls are in the OFF position, air flow will be sent to air inlet passage (5). Air pressure forces piston (4) and stem (6) downward. When stem (6) moves downward, pressure oil from passage (1) enters passage (11). When this pressure oil flows to the brake housing, the pressure oil compresses a spring. This releases the parking brakes for the rear wheels. Relief valve (2) limits system pressure.