The description of the parking brake system assumes that the service brake pedal is fully released.
Parking Brake Switch in the OFF Position
Note: The machine must be in either forward or reverse travel for the following information. The brakes are hydraulically released.
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| Illustration 1 | g06572123 |
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| Illustration 2 | g06572134 |
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(1) Speed sensor
(2) Motor solenoids (3) Brakes (4) Hystat override solenoid (5) Left side motor (6) Right side motor (7) Parking Brake Switch (8) Piston (9) Spring (10) Machine ECM (11) Parking brake solenoid | |
When parking brake switch (7) is disengaged, or has been toggled to be OFF. ECM (10) sends an energized signal to parking brake solenoid (11). The signal flows through the coil of parking brake solenoid (11) through the return to ECM (10).
As the signal flows through the coil of the parking brake solenoid (11), solenoid (11) is shifted downward. Pilot oil is routed through the hydrostatic pump. The oil flows from solenoid (11) to the brakes, the brakes are now released. The right and left piston motors are free to rotate.
Oil from solenoid (4) flows back to the hydraulic tank.
Parking Brake Switch in the ON position
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| Illustration 3 | g06572162 |
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| Illustration 4 | g06572167 |
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(1) Speed sensor
(2) Motor solenoids (3) Brakes (4) Hystat override solenoid (5) Left side motor (6) Right side motor (7) Parking Brake Switch (8) Piston (9) Spring (10) Machine ECM (11) Parking brake solenoid | |
When parking brake switch (7) is being turned on, parking brake switch (7) momentarily completes the circuit between the normally open connection and ground. The completed circuit results in a signal of 0 V to ECM (10) at the normally open contact. The ECM interprets the operator action as a request to toggle the parking brake. The parking brake is a momentary switch.
ECM (10) sends a signal of below the initialization current to the parking brake solenoid (11). The signal flows through the coil of solenoid valve (11) through the return wire to ECM (10).
Since the signal through the coil of solenoid valve (11) is below initialization, solenoid valve (11) remains in a de-energized state. Oil from the fan motor is passed through the hydrostatic pump. The oil is blocked at solenoid valve (11). Oil from pistons (8) flows through solenoid (11) back to the hydraulic tank. As the oil flows from piston (8), spring (9) forces piston (8) against brake (3). Then, the brakes are engaged.
The description of the service brake system assumes that the parking brake is disengaged and the transmission control lever is in any of the following positions:
- FORWARD
- NEUTRAL
- REVERSE
For additional information regarding the power train system, refer to Systems Operation, "Power Train Hydraulic System".
The Service Brake Pedal Released.
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| Illustration 5 | g06572176 |
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| Illustration 6 | g06572183 |
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(1) Speed sensor
(2) Motor solenoids (3) Brakes (4) Hystat override solenoid (5) Left side motor (6) Right side motor (7) Parking Brake Switch (8) Piston (9) Spring (10) Machine ECM (11) Parking brake solenoid (12) Left servo valve (13) Right servo valve (14) Left piston pump (15) Right piston pump (16) Brake pedal sensor | |
Since the ECM registers the signals as the release of the service brake pedal, the ECM does not modify any signals to the servo valves of the pumps or to the servo valves of the motors. Also, the ECM does not modify any signals to solenoid valve (11).
The Service Brake Pedal Is Partially Depressed
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| Illustration 7 | g06572189 |
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| Illustration 8 | g06572196 |
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(1) Speed sensor
(2) Motor solenoids (3) Brakes (4) Hystat override solenoid (5) Left side motor (6) Right side motor (7) Parking Brake Switch (8) Piston (9) Spring (10) Machine ECM (11) Parking brake solenoid (12) Left servo valve (13) Right servo valve (14) Left piston pump (15) Right piston pump (16) Brake pedal sensor | |
As you start to depress the service brake pedal, the duty cycle of the pulse width modulated signal from pedal position sensor increases. The signal flows from the pedal position sensor to the ECM.
As the ECM interprets the increased duty cycle, the ECM modifies the signals to the servo valves of the pumps and to the servo valves of the motors. The ECM starts to decrease the duty cycle of the pulse width modulated signals to motor solenoids (2). As the duty cycles of the signals decrease, piston motor (5) and piston motor (6) start to upstroke and the machine begins to slow down.
When the piston motors reach the maximum displacements and you continue to depress the service brake pedal, the ECM starts to decrease the duty cycle of the pulse width modulated signals to servo valve (12) and servo valve (13). As the duty cycles of the signals decrease, left piston pump (14) and right piston pump (15) start to destroke and the machine continues to slow down until the pumps reach zero angle.
The Service Brake Pedal Is Fully Depressed
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| Illustration 9 | g06572198 |
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| Illustration 10 | g06572205 |
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(1) Speed sensor
(2) Motor solenoids (3) Brakes (4) Hystat override solenoid (5) Left side motor (6) Right side motor (7) Parking Brake Switch (8) Piston (9) Spring (10) Machine ECM (11) Parking brake solenoid (12) Left servo valve (13) Right servo valve (14) Left piston pump (15) Right piston pump (16) Brake pedal sensor | |
When the service brake pedal is fully depressed, the pedal position sensor sends a pulse width modulated signal to the ECM . When the duty cycle is greater than the calibrated detent point, the ECM interprets the signal as full depression of the service brake pedal.
The ECM modifies the signals to the piston motors to return the piston motors to the maximum displacement. Also, the ECM modifies the signals to the piston pumps to return the piston pumps to zero angle.
The ECM sends a signal of 0 V from pin 6 of the J2 connector. The signal flows through wire A958-WH(White)to solenoid valve (8).
Since the signal to solenoid valve (11) is 0 V , solenoid valve (11) shifts. Charge oil from the fan pump is blocked at solenoid valve (11). Oil from pistons (8) flows through solenoid valve (11). The oil flows from solenoid (11) to the hydraulic tank. As the oil flows from pistons (8), springs (9) force pistons (8) against brakes (3). Then, the brakes are engaged.