GUIDE AS. 2747932 - Caterpillar

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.
Illustration 1 g03690691
(1) Speed sensor
(2) Motor solenoids
(3) Brakes
(4) Piston
(5) Left side motor
(6) Right side motor
(7) Spring
(8) Parking brake solenoid
(9) Hystat override solenoid
(10 ) Machine ECM
(11) Parking Brake Switch When parking brake switch (11) is disengaged or has been toggled to be OFF. ECM (10) sends an energized signal to parking brake solenoid (8). the signal flows through the coil of parking brake solenoid (8) through the return to ECM (10).As the signal flows through the coil of the parking brake solenoid (8), solenoid (8) is shifted downward. Pilot oil is routed through the hydrostatic pump. The oil flows from solenoid (8) to the brakes, the brakes are now released. The right and left piston motors are free to rotate.Oil from solenoid (8) flows back to the hydraulic tank.Parking Brake Switch in the ON position
Illustration 2 g03691911
(1) Speed sensor
(2) Motor solenoids
(3) Brakes
(4) Piston
(5) Left side motor
(6) Right side motor
(7) Spring
(8) Parking brake solenoid
(9) Transmission NEUTRAL interlock solenoid
(10 ) Machine ECM
(11) Parking Brake Switch When parking brake switch (11) is being turned on, parking brake switch (11) 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 (8). The signal flows through the coil of solenoid valve (8) through the return wire to ECM (10).Since the signal through the coil of solenoid valve (8) is below initialization, solenoid valve (8) remains in a de-energized state. Oil from the fan motor is passed through the hydrostatic pump. The oil is blocked at solenoid valve (8). Oil from pistons (4) flows through solenoid (8) back to the hydraulic tank. As the oil flows from piston (4), spring (7) forces piston (4) against brake (5). Then, the brakes are engaged.Service Brake System
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
REVERSEFor additional information regarding the power train system, refer to Systems Operation, "Power Train Hydraulic System".The Service Brake Pedal Released.
Illustration 3 g03691914
The Service brake pedal released.
(1) Speed sensor
(2) Servo valve
(3) Brake
(4) Piston
(5) Left piston motor
(6) Right piston motor
(7) Spring
(8) Parking brake solenoid
(9) Transmission NEUTRAL interlock solenoid
(10) Machine ECM
(12) Connector
(13) Servo valve
(14) Servo valve
(15) Rear piston pump
(16) Front piston pump
(17) Connector
(18) Connector
(19) Connector
(20) Brake pedal sensor
(21) Line 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 (8). The Service Brake Pedal Is Partially Depressed
Illustration