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| Illustration 1 | g00984830 |
Location of the parking brake control valve | |
The parking brake control valve is located on the left side of the front frame, in the transmission compartment.
The parking brake section of each wheel brake is applied by springs and released by oil pressure. The parking brake control valve supplies pressure oil to each wheel brake in order to release the parking brake.
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| Illustration 2 | g00880691 |
Schematic of the parking brake control valve (1) Parking brake oil pressure switch (2) Port to the parking brake section of the front wheel brakes (3) Port to the parking brake section of the rear wheel brakes (4) Pressure tap for parking brake circuit (5) Parking brake solenoid valve (6) Parking brake solenoid valve (7) Port for return oil to the hydraulic tank (8) Port for pilot supply oil for the parking brake system | |
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| Illustration 3 | g00984831 |
Parking brake control valve (1) Parking brake oil pressure switch (2) Port to the parking brake section of the front wheel brakes (3) Port to the parking brake section of the rear wheel brakes (4) Pressure tap for parking brake circuit (5) Parking brake solenoid valve (6) Parking brake solenoid valve (7) Port for return oil to the hydraulic tank (8) Port for pilot supply oil for the parking brake system | |
The parking brake control valve consists of a manifold containing two solenoid valves, a pressure switch, and a pressure tap.
Pilot oil from the brake and pilot section of the gear pump flows through the pilot oil pressure reducing valve and pilot hydraulic filters to a distribution manifold. From this manifold, the oil at the pressure reducing valve pressure setting, flows through a check valve to the parking brake control valve. This oil enters the parking brake control valve through port (8). If the parking brake switch is in the ON position, pilot oil is blocked by parking brake solenoid valve (6) and can not flow to the wheel brakes.
If the parking brake switch is moved to the OFF position, parking brake solenoid valves (5) and (6) will be energized. Pilot oil from port (8) flows through parking brake solenoid valve (6) to parking brake solenoid valve (5). When parking brake solenoid valve (5) is energized, the solenoid valve prevents the oil from returning to the hydraulic tank through port (7). Pilot oil now flows out through ports (2) and (3) to the parking brake section of the wheel brakes. This oil pressure will release the parking brakes.
If the parking brake switch is moved to the ON position, parking brake solenoid valves (5) and (6) will be de-energized. Pilot oil is blocked by parking brake solenoid valve (6) and can not flow to the wheel brakes. The parking brakes are applied by the force of the springs in the wheel brakes. Oil from the wheel brakes can return to the hydraulic tank through ports (2) and (3), parking brake solenoid valves (5) and (6), and tank port (7). Parking brake solenoid valve (5) provides an extra path for the oil to return to the hydraulic tank. This allows for a faster application of the parking brake.
Parking brake oil pressure switch (1) will signal the Power Train/Chassis Electronic Control Module when the parking brake is engaged.