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| Illustration 1 | g00985115 |
The retarder control valve is located on the left side of the front frame, in the transmission compartment.
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| Illustration 2 | g00916112 |
Schematic of the retarder control valve (1) Front residual brake oil/stop light pressure switch (2) Front service brake and retarder oil pressure switch (3) Port to the front service brakes (4) Port to the rear service brakes (5) Rear service brake and retarder oil pressure switch (6) Rear residual brake oil/stop light pressure switch (7) Port from the rear brake accumulator (8) Retarder supply solenoid valve for the rear brakes (9) Port from the rear brake section of the service brake control valve (10) Port from the accumulator charging valve (11) Shuttle valve for the rear brakes (12) Port from the front brake accumulator (13) Retarder supply solenoid valve for the front brakes (14) Retarder control valve for the rear brakes (15) Shuttle valve for the front brakes (16) Port from the front brake section of the service brake control valve (17) Port from the accumulator charging valve (18) Retarder control solenoid valve for the front brakes (19) Port for return oil to the hydraulic tank (20) Port to the front brake section of the service brake control valve (21) Port to the rear brake section of the service brake control valve | |
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| Illustration 3 | g00985116 |
Retarder control valve (1) Front residual brake oil/stop light pressure switch (2) Front service brake and retarder oil pressure switch (3) Port to the front service brakes (4) Port to the rear service brakes (5) Rear brake and retarder oil pressure switch (6) Rear residual brake oil/stop light pressure switch (7) Port from the rear brake accumulator (8) Retarder supply solenoid valve for the rear brakes (9) Port from the rear brake section of the service brakes control valve (10) Port from the accumulator charging valve (11) Shuttle valve for the rear brakes (12) Port from the front brake accumulator (13) Retarder supply solenoid valve for the front brakes (14) Retarder control solenoid valve for the rear brakes (15) Shuttle valve for the front brakes (16) Port from the front brake section of the service brake control valve (17) Port from the accumulator charging valve (18) Retarder control solenoid valve for the front brakes (19) Port for the return oil to the hydraulic tank (20) Port to the front brake section of the service brake control valve (21) Port to the rear brake section of the service brake control valve | |
The hydraulic circuits for the front service brakes and for the rear service brakes are separate. The retarder control valve contains two solenoid valves, two pressure switches, and one shuttle valve for each brake circuit.
The retarder control valve modulates the oil supply to the service brakes when either the retarder lever is moved to the ON position, or the Automatic Retarder Control (ARC) is activated.
The retarder control valve also supplies pressure oil from the brake accumulators to the service brake control valve. With the service brake pedal depressed, oil from the service brake control valve flows through the retarder control valve to apply the service brakes.
Oil from the accumulator charging valve flows through ports (10) and (17) and through ports (7) and (12) to the brake accumulators. The accumulator charging valve maintains a constant pressure to the brake accumulators, while the engine is running.
Pressure oil from the brake accumulators enters the retarder control valve through ports (7) and (12). Pressure oil from the rear brake accumulator enters through port (7) and is directed to retarder supply solenoid valve (8). This oil also flows through port (21) to the rear brake section of the service brake control valve. Pressure oil from the front brake accumulator enters through port (12) and is directed to retarder supply solenoid valve (13). This oil also flows through port (20) to the front brake section of the service brake control valve.
When the ARC switch is in the OFF position and the retarder lever is in the OFF position, pressure oil from the brake accumulators will not flow through supply solenoid valves (8) and (13). If the ARC switch is in the ON position and the engine speed is within 50 rpm of the programmed setting, or if the retarder lever is moved to the ON position, retarder supply solenoid valves (8) and (13) will be energized. When retarder supply solenoid valve (8) is energized, pressure oil from the rear brake accumulator will flow through solenoid valve (8) to retarder control solenoid valve (14). When retarder supply solenoid valve (13) is energized, pressure oil from the front brake accumulator will flow through solenoid valve (13) to retarder control solenoid valve (18). Either the required level of braking from the ARC or the position of the retarder lever will determine the amount that retarder control solenoid valves (14) and (18) will open.
Retarder control solenoid valves (14) and (18) will allow pressure oil to flow to shuttle valves (11) and (15). Shuttle valves (11) and (15) prevent pressure oil from flowing through ports (9) and (16), through the service brake control valve to the hydraulic tank. Pressure oil from retarder control solenoid valve (14) flows through shuttle valve (11) and through port (4) to the rear service brakes. Pressure oil from retarder control solenoid valve (18) flows through shuttle valve (15) and through port (3) to the front service brakes.
When the retarder lever is in the OFF position or the ARC is de-activated, retarder supply solenoid valves (8) and (13) and retarder control solenoid valves (14) and (18) are de-energized. Pressure oil in the service brakes returns through shuttle valves (11) and (15). Oil then flows through retarder control solenoid valves (14) and (18) and through port (19) to the hydraulic tank.
Pressure oil from the front brake accumulator and from the rear brake accumulator is also supplied to the service brake control valve through ports (20) and (21). If the operator depresses the service brake pedal, oil from the service brake control valve will enter the retarder control valve through ports (9) and (16). Oil then flows to shuttle valves (11) and (15). Shuttle valves (11) and (15) will prevent pressure oil from flowing through retarder control solenoid valves (14) and (18) to the hydraulic tank. Pressure oil from the rear brake section of the service brake control valve enters through port (9), flows through shuttle valve (11) and through port (4) to the rear service brakes. Pressure oil from the front brake section of the service brake control valve enters through port (16), flows through shuttle valve (15) and through port (3) to the front service brakes.
There are four pressure switches located in the top of the retarder control valve. The pressure switches will close when the service brakes and/or retarder are applied. Pressure switches (1) and (2) are for the front brake circuit. Pressure switches (5) and (6) are for the rear brake circuit. Pressure switches (1) and (6) operate the stop lights at the rear of the machine and the residual brake pressure indicator on the dash. Pressure switches (2) and (5) will signal the Power Train/Chassis ECM that the brakes are applied.