Introduction

Location Of Components
(1) Brake interlock valve. (2) Cooling and test manifold. (3) Steer pump. (4) Brake solenoid valve. (5) Pressure switch. (6) Brake switch. (7) Front gear reducer.

The secondary/parking brake is used to hold a stopped or parked machine in place. It is also used in an emergency to stop the machine if the primary service brake fails.

The hydrostatic propel system serves as the primary service brake normally used to stop the machine. The primary service brake operates when the propel lever is moved to the STOP position. This creates hydrostatic braking, which stops the machine.

Hydraulic System

Secondary/Parking Brake Hydraulic System Schematic
(1) Cooling and test manifold. (2) Brake solenoid valve. (3) Pressure switch. (4) Brake switch. (5) Brake interlock valve. (6) Propel pumps. (7) Hose to hydraulic oil tank. (8) Steer pump. (9) Hose to steer system. (10) Front gear reducer.

Front Gear Reducer
(10) Front gear reducer.

The secondary/parking brake is a multiple-disc oil-bathed type, located in front gear reducer (10). The secondary/parking brake is spring-applied and hydraulically released. The operator releases the brake by sending hydraulic pressure to the front gear reducer. If, for any reason, hydraulic pressure is lost, the secondary/parking brake is automatically applied.

Steer Pump
(8) Steer pump.

Hydraulic oil for the secondary/parking brake system comes from the primary outlet of steer pump (8).

Brake Solenoid Valve And Pressure Switch
(2) Brake solenoid valve. (3) Pressure switch.

Oil from the steer pump is routed to pressure switch (3) and brake solenoid valve (2). Brake solenoid valve (2) is controlled by brake switch (4).

Brake Switch
(4) Brake switch.

When the operator pushes brake switch (4) down, oil from the steer pump is blocked at brake solenoid valve (2). Oil at front gear reducer (10) flows through brake solenoid valve (2) to the hydraulic oil tank through hose (7). Springs in the front gear reducer apply the secondary/parking brake, stopping the machine or holding it in place. A lamp, located in brake switch (4) will light. This indicates that the secondary/parking brake is applied and the machine should not be moved.

When the operator pulls brake switch (4) up, the position of brake solenoid valve (2) is determined by pressure switch (3). If hydraulic oil pressure is high enough to release the secondary/parking brake, pressure switch (3) will open. Oil is ported through brake solenoid valve (2) to front gear reducer (10). This releases the secondary/parking brake, allowing the machine to move. The lamp in brake switch (4) will be off. This indicates the secondary/parking brake is released and the machine may be moved.

If hydraulic oil pressure drops, pressure switch (3) will close. Oil is blocked at brake solenoid valve (2), applying the secondary/parking brake. The lamp in brake switch (4) will light, indicating that the machine should not be moved.

Cooling And Test Manifold
(1) Cooling and test manifold.

Hydraulic oil to the front gear reducer is also routed to cooling and test manifold (1). Test port X4 on the cooling and test manifold can be used to measure the pressure of the oil to front gear reducer (10).

Brake Interlock Valve
(5) Brake interlock valve.

Brake interlock valve (5) is in the normally open (de-energized) position and prevents the machine from moving by equalizing the servo control pressures on either end of the swashplates for propel pumps (6).

Electrical System

Secondary/Parking Brake Electrical System Schematic
(1) Brake switch. (2) Pressure switch. (3) Brake solenoid valve. (4) Shift solenoid valve. (5) Brake interlock valve.

Oil flow through brake solenoid valve (3) is electrically controlled by brake switch (1) and pressure switch (2). The operator sets the position of brake switch (1) by pushing the button down, or pulling it up. The position of pressure switch (2) is determined by the pressure of the hydraulic oil in the system.

The positions of brake switch (1) and pressure switch (2) determine whether electrical current is sent to brake solenoid valve (3) and brake interlock valve (5). When current is not sent to the brake solenoid valve and brake interlock valve, the secondary/parking brake is applied and the machine may not be moved. When current is sent to the brake solenoid valve and brake interlock valve, the secondary/parking brake is released and the machine may be moved.

Brake Applied

When the operator pushes the secondary/parking brake button down, current flows through brake switch (1) and the brake indicator light will be on. No current is sent through pressure switch (2), brake solenoid valve (3) or brake interlock valve (5). Brake solenoid valve (3) and brake interlock valve (5) are de-energized. The brake solenoid valve blocks hydraulic oil from pressure switch (2) and the front gear reducer, and the secondary/parking brakes remain applied. The brake interlock valve prevents the machine from moving by equalizing the servo control pressures on either end of the swashplates for the two propel pumps.

Brake Released

When the operator pulls the brake button up, current flows through brake switch (1) to brake solenoid valve (3) and brake interlock solenoid (5). The brake solenoid valve will be energized, sending hydraulic oil to pressure switch (2) and the front gear reducer, releasing the secondary/parking brake. The machine still will not move because the ground path for brake interlock valve (5) is broken by pressure switch (2). When the pressure of the hydraulic oil at pressure switch (2) is at least 1965 kPa (285 psi), the pressure switch closes, completing the ground path for the brake interlock valve. When the ground path is complete the brake interlock solenoid is energized. This allows a pressure differential across the servo piston of both propel pumps. The servo pistons move the swashplates which cause the propel pumps to send high pressure oil to the rear propel motor and drum drive motor to propel the machine. This releases the secondary/parking brake. This will complete the path to ground for brake interlock valve (5). The brake interlock valve will be energized, allowing the machine to move when the operator moves the propel lever.

If the pressure of the hydraulic oil at pressure switch (2) falls below 1965 kPa (285 psi) the pressure switch opens, and the brake interlock valve is de-energized. When the brake interlock valve is de-energized, charge oil pressure is sent to both ends of the servo pistons of both propel pumps. When the pressure on both sides of the servo pistons is equal, the pump swashplates do not move, and the propel pumps dot not send high pressure oil to the rear propel motor and drum drive motor.

Solenoid Valve

Solenoid Valve
(1) Working port. (2) Cartridge. (3) Inlet port. (4) Coil. (5) Tank port.

The solenoid valve is an electrically-operated two-position valve. The valve is used to route hydraulic oil to the front gear reducer to release the secondary/parking brake.

Inlet port (3) is connected to the primary outlet of the steer pump. Working port (1) is connected to the front gear reducer and the cooling and test manifold. Tank port (5) is connected to a return line leading to the hydraulic oil tank.

When no electrical current is sent to the solenoid valve, coil (4) is de-energized. Hydraulic oil from the steer pump enters the solenoid valve at inlet port (3). The pressure of this oil will be approximately 2070 kPa (300 psi) at low idle.

Hydraulic oil from inlet port (3) is blocked at cartridge (2). Working port (1) is open tank port (5). Any brake pressure at the front gear reducer drains through the solenoid valve to the hydraulic oil tank. This applies the secondary/parking brake, stopping the machine or holding it in place.

When electrical current is sent to the solenoid valve, coil (4) is energized. This moves a spool inside cartridge (2). Hydraulic oil from the steer pump enters the solenoid valve at inlet port (3). This oil is ported through cartridge (2) to working port (1). Tank port (5) is blocked. Oil exits the solenoid valve through working port (1), and is routed to the front gear reducer, the pressure switch and the cooling and test manifold. This releases the secondary/parking brake, allowing the machine to move.

Front Gear Reducer

Brake Components Of Front Gear Reducer
(1) Sun shaft. (2) Outside clutch discs. (3) Inside clutch discs. (4) Disc carrier. (5) Brake port. (6) Piston. (7) Output shaft. (8) Spring.

The front gear reducer contains a variable-displacement hydraulic motor, a double-reduction planetary gear reducer and the secondary/parking brake.

The variable-displacement hydraulic motor turns output shaft (7). Sun shaft (1) provides input to the double reduction planetary gear reducer. This provides propulsion to the drum.

Disc carrier (4) is connected to sun shaft (1) by splines. Inside clutch discs (3) are connected to disc carrier (4) by splines. Outside clutch discs (2) are held stationary by the front gear reducer, and do not rotate.

When the secondary/parking brake is applied, spring (8) holds piston (6) against outside clutch discs (2) and inside clutch discs (3). Clutch discs (2) and (3) are pressed together, keeping disc carrier (4) from turning. Disc carrier (4) holds sun shaft (1) and output shaft (7) stationary. This prevents the drum from turning, stopping the machine or holding it in place.

When the operator releases the brake, hydraulic oil from the solenoid valve enters the front gear reducer at port (5). This oil is ported to the left side of piston (6). The piston moves to the right, compressing spring (8). This removes friction between outside clutch discs (2) and inside clutch discs (3).

Inside clutch discs (3) and disc carrier (4) turn freely with output shaft (7) and sun shaft (1). This allows the drum to rotate, and the machine can move.