Usage:
General Information
SMCS Code:4250
Hydraulic Schematic for the Braking System
Location of the Braking System Components
The braking system has two brake control circuits operating four wheel brakes on the machine: a service brake circuit and a parking brake circuit. When the machine is equipped with an optional towing brake release system, the braking system also includes this additional circuit.
The main components of the service brake circuit are: hydraulic tank (22), brake and pilot pump (20), check valve (19), brake accumulator charging valve (7), rear brake accumulator (1), front brake accumulator (2), service brake and transmission neutralizer pedal (3), service brake pedal (4), service brake control valve (5), rear wheel brakes (6), front wheel brakes (14) and various lines.
The main components of the parking brake circuit are: hydraulic tank (22), brake and pilot pump (20), check valve (19), pilot oil pressure reducing valve (21), parking brake control valve (15), rear wheel brakes (6), front wheel brakes (14) and various lines.
Location of the Hydraulic Tank
Hydraulic tank (22) is located in the middle of the right side of the machine behind the hydraulic tank guard. Additional oil is placed into the tank through filler cap (24).
Location of the Vacuum Breaker/Relief Valve
Vacuum breaker/relief valve (23) is mounted on hydraulic tank (22).
Location of the Steering, Brake and Pilot Pump
Brake and pilot pump (20) is part of a two-section, gear-type pump mounted on the torque converter updrive housing. Check valve (19) is connected to the outlet port of the brake and pilot pump.
Location of the Brake Accumulator Charging Valve
Brake accumulator charging valve (7) is mounted on the left side of the rear frame in the transmission compartment.
Location of the Service Brake Accumulators
Rear brake accumulator (1) and front brake accumulator (2) are mounted on the left side of the rear frame in the torque converter equipment.
Location of the Service Brake Pedal
Service brake and transmission neutralizer pedal (3) and service brake pedal (4) are mounted to the floor panel of the operator's compartment. The service brake control valve is located below the floor panel and is connected to the brake pedals by a mechanical linkage.
Location of the Pilot Oil Pressure Reducing Valve
Pilot oil pressure reducing valve (21) is mounted on the left side of the rear frame in the transmission compartment.
Location of the Parking Brake Control Valve
Parking brake control valve (15) and solenoid valves (26) are mounted on the left side of the rear frame in the transmission compartment.
Location of the Wheel Brake Groups
The wheel brake groups are mid-mounted in the axle housings, between the differentials and final drives. Front wheel brake groups (14) are located in the axle housing at the front of the machine.
Service and Parking Brake System
SMCS Code:4251; 4267
Hydraulic Schematic for the Service and Parking Brake System
Each wheel brake is divided into two sections. The service brake is an oil pressure applied and spring released brake section. The parking brake is an oil pressure released and spring applied brake section. The service brake can be used when the parking brake is released.
The service wheel brakes are controlled by two brake pedals in the operator's station. The left and right brake pedal assemblies are connected by a mechanical linkage. When right pedal (4) is depressed only the wheel brakes are applied. When left pedal (3) is depressed, the wheel brakes are applied, and the transmission is neutralized. This allows the full engine power to be used in the hydraulic system. When left pedal (3) is released, the transmission engages and the wheel brakes are released.
With the engine running, oil flows from hydraulic tank (18) to brake and pilot pump (16) which is part of the steering, brake and pilot pump group. The oil then flows from brake and pilot pump (16) through check valve (15) and into accumulator charging valve (7).
The pistons in the accumulators are held against the oil intake ends with dry nitrogen gas at a pressure of approximately 5515 kPa (800 psi). Accumulator (1) stores hydraulic oil pressure for the operation of the rear brakes. Accumulator (2) stores hydraulic oil pressure for the front brakes.
After the brakes have been activated several times, the volume of oil in the accumulators is less. When there is a decrease of oil pressure in an accumulator to 11 725 ± 345 kPa (1700 ± 50 psi), accumulator charging valve (7) routes oil from brake and pilot pump (16) to the accumulator. When accumulator oil pressure rises to 14 485 ± 345 kPa (2100 ± 50 psi), shuttle valves block the flow of oil to the accumulator and cause the oil to return to the hydraulic tank. The accumulator charging process works the same whether one or both accumulators need to be recharged.
From the accumulators, the oil flows to service brake control valve (5). Service brake control valve (5) is a tandem valve that routes brake oil to both the front and rear axle service brakes.
When a brake pedal is depressed, oil flows through service brake control valve (5) where pressure to the wheel brakes is reduced to 4310 ± 345 kPa (625 ± 50 psi). Oil flows out of the top port to rear wheel brakes (6), and out the bottom port to front wheel brakes (11). Oil pressure is approximately 345 kPa (50 psi) higher for the rear wheel brakes than that of the front wheel brakes.
Oil pressure flows into the service brake section of the wheel brakes and acts against the service brake piston, causing the machine to slow down or stop.
The parking brake is controlled by a knob on the operator's station dash panel. The parking brake will not disengage until the engine is running and the service brake oil pressure reaches approximately 8270 kPa (1200 psi). The brake will automatically engage if brake system oil pressure is low. When the parking brake control knob is moved to the engaged position, all wheel brakes are activated.
With the engine running, oil flows from brake and pilot pump (16) through pilot oil pressure reducing valve (17) to parking brake control valve (12). Pilot oil pressure reducing valve (17) reduces pilot oil pressure for the pilot circuit. Pressure reducing valve (17) is set at 3515 ± 70 kPa (510 ± 10 psi).
When the parking brake control knob in the operator's station is moved to the disengaged position, the solenoids of parking brake control valve (12) are energized. Oil flows through parking brake control valve (12) to both axles. Oil pressure then disengages the parking brake in each wheel brake assembly.
The parking brake control valve solenoids are de-energized when the parking brake control knob is moved to the engaged position, or the engine start switch key is turned to the OFF position. This will cause parking brake control valve (12) to return the parking brake oil to hydraulic tank (18). The parking brakes are now engaged.
If the parking brake is engaged due to a machine fault and the machine must be towed, the machine parking brakes can be released manually.
Reference: For information on manually releasing the parking brakes, refer to Systems Operation, Testing and Adjusting, "Parking Brake Manual Release" for the machine that is being serviced.
Certain Elphinstone machines fitted with remote controls may be equipped with an optional towing brake release system. If the parking brake is engaged due to a machine fault and the machine must be towed, the towing brake release system can be used to release the machine parking brakes.
Reference: For information on the towing brake release system, refer to Systems Operation, Testing and Adjusting, "Towing Brake Release System" for the machine that is being serviced.
Gear Pump (Pilot and Braking)
SMCS Code:5073-P&B
Location of the Steering, Brake and Pilot Pump
Brake and pilot pump (1) is part of a two-section, gear-type pump mounted on the torque converter updrive housing. The brake and pilot pump is a fixed displacement pump which supplies oil to the parking brake circuit, service brake circuit, implement pilot circuit and the STIC steering pilot circuit.
Accumulator Charging Valve (Brake)
SMCS Code:4264
The function of accumulator charging valve is to keep oil pressure in the two service brake accumulators within a constant range while the engine is running. The accumulator charging valve controls the flow of oil to the brake accumulators.
Location of the Brake Accumulator Charging Valve
Port Locations for the Accumulator Charging Valve
Schematic for the Brake Accumulator Charging Valve
Oil from the brake and pilot pump flows into the brake accumulator charging valve at port (2). Inside the accumulator charging valve the oil acts against relief valve (6). The relief valve limits brake oil pressure to 17 930 ± 690 kPa (2600 ± 100 psi).
The oil then goes to flow control valve (8). Flow control valve (8) regulates the flow of oil to the brake circuit. Any excess oil that is not required by the brake circuit is diverted back to the hydraulic oil tank.
NOTE: Flow control valve (8) contains shims that set the standby pressure. A standby pressure of 4310 ± 210 kPa (625 ± 30 psi) is available from the brake and pilot pump when the brake accumulators do not require charging.
Oil now flows from flow control valve (8) through check valve (10) to load sensing spool (11). Check valve (10) prevents oil from flowing back through the accumulator charging valve to the brake and pilot pump or pilot system.
Load sensing spool (11) is for controlling the cut-in and the cut-out pressures for the brake accumulator charging valve. When the oil pressure in the brake circuit reaches the cut-in pressure of 11 725 ± 345 kPa (1700 ± 50 psi), spool (11) shifts. The movement of spool (11) causes the spool in flow control valve (8) to also shift. This allows oil to flow to inverse shuttle check valve (12). The movement of inverse shuttle check valve (12) allows the oil to charge the brake accumulators.
When the oil pressure in the brake circuit reaches the cut-out pressure of 14 485 ± 345 kPa (2100 ± 50 psi), spool (11) shifts in the opposite direction. This causes the spool in flow control valve (8) to also shift. This stops the flow of oil to inverse shuttle check valve (12).
Oil flows through inverse shuttle check valve (12) to the brake accumulators during oil charge. Pressurized oil from inverse shuttle check valve (12) flows to the oil end of the two brake accumulators, but the oil flow between the two brake accumulators is kept separate. Inverse shuttle check (12) is designed to charge each brake accumulator when the pressure reaches the cut-in pressure.
A third port in inverse shuttle check valve (12) connects to the brake oil pressure switches.
Brake Accumulator
SMCS Code:4263
Location of the Service Brake Accumulators
The two brake accumulators are located on the left side of the rear frame in the torque converter compartment.
Service Brake Accumulator
Each accumulator has a sealed piston (6) that moves up and down inside the bore of the accumulator. Chamber (7) above the piston has a charge of dry nitrogen gas. The dry nitrogen gas is put into the accumulator through nitrogen charging valve (8). The chamber of dry nitrogen gas needs a charge of approximately 5515 kPa (800 psi).
Oil from the accumulator charging valve flows in through port (3). The oil then enters pressure oil chamber (4). This oil pushes piston (6) up which causes the dry nitrogen gas to compress. When the pressure in the accumulator reaches 14 485 ± 345 kPa (2100 ± 50 psi), the supply of oil is stopped by the accumulator charging valve.
When the operator pushes down on either brake pedal, the oil from the chamber (4) flows out of port (3). The oil flows from port (3) through the service brake control valve in order to apply the service brakes.
Brake Control Valve (Service)
SMCS Code:4265
Location of the Service Brake Pedals
Service brake and transmission neutralizer pedal (1) and service brake pedal (2) are mounted to the floor panel of the operator's compartment. The service brake control valve is located below the floor panel. A mechanical link connects the two brake pedals to each other. When a brake pedal is depressed, a roller on the cross shaft assembly actuates the service brake control valve.
The control valve is a dual pressure reducing valve with two independent output pressures.
Service Brake Control Valve
Modulation of the pressurized oil in the accumulators to the service brakes is controlled by the service brake control valve. The position of either brake pedal (1) or (2) causes a specific pressure at the service brakes. As the position of the pedal changes, the pressure at the service brake also changes. The service brake control valve will modulate this pressure and allow a maximum of 4310 ± 345 kPa (625 ± 50 psi) at the wheel brakes.
View A-A of the Service Brake Control Valve
When the operator pushes on a brake pedal, a roller on the brake pedal assembly forces piston (3) downward. Piston (3) applies a force on springs (4), (5) and (6). The force of springs (4) and (5) moves retainer (7) and ball (8). Movement of retainer (7) and ball (8) causes upper valve spool (10) to move away from the seat in spacer (9).
The movement of upper valve spool (10) causes movement of lower valve spool (18) and the compression of spring (24). When valve spools (10) and (18) move, oil flow through passages (13) and (21) to the hydraulic oil tank is blocked.
This allows pressurized oil from accumulator ports (15) and (23) to flow through passages (13), (16), (21) and (22). The oil then flows through passages (12) and (20) in order to apply the service brakes. At the same time, pressurized oil flows into cavities (17) and (25) and through passages (16) and (22). The oil pressure at the service brakes has the same pressure as the oil in cavities (17) and (25).
Oil pressure in cavity (25) and the force of spring (24) act to balance lower valve spool (18) against the force of the pressure in cavity (17). In the same manner, pressure in cavity (17) creates a force against the bottom of upper valve spool (10). The upper valve spool is balanced by the force of springs (4) and (5) at the top of spool (10).
The force of springs (4), (5) and (6) is balanced by the force that is applied to the pedal. Upward movement of valve spools (10) and (18) causes accumulator ports (15) and (23) to be covered. The level of pressure in the independent valve sections creates a feedback force. This allows the operator to modulate the pressure to the service brakes.
Valve spools (10) and (18) balance between the ports for the hydraulic oil tank and the ports for the service brakes. This is done in order to maintain the brake pressure until the position of the pedal changes. The change in the pedal position means that more brake pressure or less brake pressure is necessary.
If piston (3) is moved downward in order to apply more compression on springs (4) and (5), valve spools (10) and (18) will move. The valve spools move in order to allow more pressure oil to flow to outlets (12) and (20) to the service brakes. This results in a higher oil pressure in cavities (17) and (25), which is required to maintain the balance of valve spools (10) and (18).
NOTE: The service brake control valve meters oil pressure to the rear brakes at approximately 345 kPa (50 psi) higher than the pressure to the front brakes.
Wheel Brakes
SMCS Code:4251; 4267
Wheel Brake Assembly
The service and parking brakes are oil immersed, multi-disc type and are located in each axle housing between the differential and final drives. The heat created from the friction of the brakes is removed by the oil in the axle housing. Each wheel brake assembly consists of a service brake piston (5), a parking brake piston (11), four guides (2) and four springs (3), fourteen springs (9) and (10), four brake discs (6), five plates (7) and a hub assembly (14). The service brakes are hydraulically applied and spring released. The parking brakes are applied by springs and released by hydraulic oil pressure.
Spindle (15) is attached to axle housing (8), which does not turn. There are slots on the inside of spindle (15). Tabs on the outside circumference of plates (7) fit in the slots in spindle (15). Hub (14) is connected by splines to axle shaft (16). Hub (14) has splines on the outside circumference which fit in the splines on the inside circumference of brake discs (6). Both a wheel assembly, which is attached to spindle (15), and brake discs (6) turn together.
When the parking brake is disengaged, oil pressure from the parking brake control valve flows through passage (13) into chamber (12) of axle housing. The pressure of the oil in chamber (12) moves parking brake piston (11) to the left, compressing springs (9) and (10), until the piston contacts the housing. Service brake piston (5) is pulled to the left by guides (2) and springs (3). Brake discs (6), hub (14) and axle shaft (16) are free to rotate.
When the parking brake is engaged, the oil in chamber (12) flows back through passage (13) and the parking brake control valve to the hydraulic oil tank. With no oil pressure behind parking brake piston (11), the force of springs (9) and (10) move the piston to the right and pushes service brake piston (5) against plates (7) and brake discs (6). The friction between the plates and the brake discs prevent brake discs (6), hub (14) and axle shaft (16) from rotating. The parking brake is engaged.
When the operator applies the service brakes (with the parking brake disengaged), pressurized oil flows from the service brake control valve through passage (1) into chamber (4), which is located behind piston (5). Oil in chamber (4) moves piston (5) to the right against plates (7) and brake discs (6). This causes friction between plate (7) and brake discs (6). The friction from brake discs (6) and plates (7) causes wheel rotation to slow down. When the friction is great enough, the wheels will stop rotating. The amount of brake application is determined by the position of the brake pedal.
Grooves are cut in the faces of brake discs (6). These grooves permit the passage of cooling oil between plates (7) and brake discs (6). When the service brakes are in the applied position or in the released position, cooling oil passes between plates (7) and brake discs (6). When brake discs (6) have adequate groove depth, cooling oil will continuously flow between brake discs (6) and plates (7).
When the brake pedal is released, oil from chamber (4) flows back through passage (1) and the service brake control valve to the hydraulic oil tank. Guides (2) and springs (3) pull piston (5) away from plates (7). The flow of oil between plates (7) and brake discs (6) helps to separate the stack as the service brakes are released.
If the machine loses power, or if the brake and pilot pump fails, the service brakes can still be applied. The pressure in the nitrogen charged accumulators for the service brakes allows several application of the brake pedals. This is for stopping the machine or for slowing the machine before engaging the parking brake.
Pressure Reducing Valve (Pilot Hydraulic System)
SMCS Code:5467-PS
Oil pressure from the brake and pilot pump is reduced by pilot oil pressure reducing valve (1) for the parking brake and pilot circuits. The parking brake circuit oil pressure is maintained at the reducing valve pressure setting.
Location of the Pilot Oil Pressure Reducing Valve
Pilot Oil Pressure Reducing Valve
Oil from the brake and pilot pump enters pilot oil pressure reducing valve (1) through inlet (3). Pilot oil pressure reducing valve (1) is a cartridge type valve that maintains pilot pressure at 3315 ± 70 kPa (510 ± 10 psi).
Reduced pressure oil flows to the parking brake control valve and pilot circuit through outlet (4). Excess oil returns to the hydraulic oil tank through outlet (2).
Brake Control Valve (Parking)
SCMS Code:4282
Parking Brake Control Valve
The parking brake control valve has two solenoids (3) controlled by a parking brake switch in the operator's station. The optional remote control system when fitted also controls the operation of solenoids (3).
Schematic for the Parking Brake Control Valve
When the engine is running and the parking brake switch is in the engaged position, no power is supplied to the solenoids (3). Oil pressure from the pilot oil pressure reducing valve in port (2) is stopped by valve spools (9). The wheel brakes are engaged by the force of the parking brake springs. Oil from the wheel brakes is free to return to the hydraulic oil tank through port (6), valve spools (9) and tank port (5).
When the parking brake switch is moved to the disengaged position, power is supplied to solenoids (3). Solenoids (3) energize and move valve spools (9) downward. Oil pressure from the pilot oil pressure reducing valve at port (2) flows through valve spools (9) and port (6) to the wheel brakes. Oil pressure releases the wheel brakes and allows the machine to move.
Machines equipped with the optional towing brake release system contain a sequence valve which is connected to port (7) of the parking brake control valve. When the parking brake is disengaged, oil pressure is directed through port (7) to the towing brake release sequence valve. The towing brake release sequence valve ensures that when the parking brake is disengaged during normal machine operation, the towing brake release system is disabled.
Parking Brake (Automatic Application)
SMCS Code:4267-AU
Low Service Brake Oil Pressure
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Personal injury could result from the sudden stop of the machine. The parking brake is automatically engaged when brake oil pressure drops below and adequate operating pressure. If the brake system oil pressure drops below normal operating pressure, the action alarm will sound. The low brake oil pressure indicator and the action light will start flashing. If the pressure drops further, the parking brake will engage automatically, the parking brake indicator on the operator's panel will come on and the transmission will shift to neutral. Be prepared for a sudden stop. Correct the reason for the loss of a brake oil pressure. Do not move the machine without normal brake oil pressure. |
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Location of the Service Brake Hydraulic Oil Pressure Switch
If a machine service brake system failure occurs and service brake hydraulic oil pressure is lost, the machine parking brake will automatically engage.
When the machine is started, service brake hydraulic oil pressure increases. When the pressure reaches approximately 9500 kPa (1380 psi), switch (1) will close. This will cause the low brake oil pressure light on the Caterpillar Monitoring System panel to go out. The parking brake can now be disengaged.
If the service brake hydraulic oil pressure decreases to 8300 ± 345 kPa (1200 ± 50 psi), switch (1) will open and the low brake oil pressure light on the Caterpillar Monitor System panel will come on. This will warn the operator of low service brake hydraulic oil pressure. If machine operation is continued and the service brake hydraulic oil pressure decreases to 6890 ± 345 kPa (1000 ± 50 psi), switch (2) will open and the parking brake will automatically engage.
Low Transmission Oil Pressure
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Personal injury could result from the sudden stop of the machine. The parking brake is automatically engaged when transmission oil pressure drops below and adequate operating pressure. If the transmission oil pressure drops below normal operating pressure, the action alarm will sound. The Impending Brake Application (IBA) indicator and the action light will start flashing. If the pressure drops further, the parking brake will engage automatically, the parking brake indicator on the operator's panel will come on and the transmission will shift to neutral. Be prepared for a sudden stop. Correct the reason for the loss of transmission oil pressure. |
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Location of the Transmission Oil Pressure Switches
Switches (1) and (2) sense transmission oil pressure. If the transmission oil pressure drops significantly, the machine parking brake will automatically engage. This may be caused by a transmission hydraulic failure, a stalled engine, or other failure.
During normal machine operation, transmission oil pressure will be 2685 ± 115 kPa (390 ± 17 psi). If the transmission oil pressure drops to 230 ± 20 kPa (33 ± 3 psi), switch (2) will open. This will cause the Impending Brake Application (IBA) light on the Caterpillar Monitor System panel come on.
If the transmission oil pressure drops further to 120 kPa (17 psi), switch (1) will open. This will cause the parking brake to automatically engage.
Reference: For information on the electrical circuits for the automatic brake application system, refer to the Electrical Schematic for the machine that is being serviced.
Braking System Switches
SMCS Code:4250-ZS
Limit Switch (Transmission Neutralizer)
Location of the Transmission Neutralizer Switch
NOTE: Both the neutralizer switch and stop light switch are located in the left pedal assembly.
When left brake pedal (1) is depressed transmission neutralizer switch (2) will open. A signal is sent to the electronic transmission control. The control module will shift the transmission to neutral. The service brakes will be progressively applied as left brake pedal (1) is depressed further.
The transmission neutralizes by de-energizing the direction clutch solenoid. At the same time, the speed clutch is still energized. This allows full engine power to be used in the hydraulic system.
When the left brake pedal is released, switch (2) will close and the transmission will engage before the service brakes are released. This action keeps the machine from free movement (rolling) when the machine is on a slope.
Reference: For the correct adjustment procedure for the transmission neutralizer switch, refer to Systems Operation, Testing and Adjusting, "Limit Switch (Transmission Neutralizer) - Adjust" for the machine that is being serviced.
Limit Switch (Stop Light)
Location of the Stop Light Switch
Stop light switch (2) is located in the left brake pedal assembly. A cross-shaft assembly connects the right brake pedal assembly to the left brake pedal assembly. When either brake pedal is depressed, stop light switch (2) will close. Power will now be supplied to illuminate stop light (3).
Rear of Operator's Station
Reference: For the correct adjustment procedure for the stop light switch, refer to Braking System Specifications, "Limit Switch (Stop Light)" for the machine that is being serviced.
Pressure Switches (Parking Brake Oil)
Location of the Parking Brake Oil Pressure Switches
The parking brake oil pressure switches are located on the parking brake control valve.
Parking brake oil pressure switch (1) is an input of the electronic transmission control and signals that the parking brake is engaged. When the parking brake is engaged, the electronic transmission control operates the alert indicator light on the Caterpillar Monitoring System panel and neutralizes the transmission if the machine is in either first speed forward or first speed reverse.
When the parking brake is disengaged and the parking brake oil pressure increases above approximately 2550 kPa (370 psi), switch (1) will open. The parking brake indicator light on the Caterpillar Monitoring System panel will go out and the transmission will operate normally.
When the parking brake is engaged or the parking brake oil pressure drops below 1800 ± 75 kPa (261 ± 25 psi), switch (1) will close. This will cause the transmission to neutralize (if the machine is in first speed) and activate the parking brake indicator light on the Caterpillar Monitoring System panel.
Rear of Operator's Station
Some machines equipped with the optional remote control system may also be equipped with an optional remote control parking brake light.
When the machine is operated on remote control and the parking brake is engaged or parking brake oil pressure drops below 1800 ± 175 kPa (261 ± 25 psi), switch (2) will close. This will cause remote control parking brake light (3) to illuminate.
When the parking brake is disengaged and parking brake oil pressure increases above approximately 2550 kPa (370 psi), switch (2) will open and remote control parking brake light (3) will go out.
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Do not operate the machine if the amber light on the operator's station is ON. This indicates the machine has either low brake oil pressure or the parking brake is engaged. Driving the machine with the parking brake engaged for an extended period will cause severe damage to the braking system. |
Pressure Switches (Residual Brake Oil)
Location of the Residual Brake Oil Pressure Switches (Behind Dash Panel)
Residual Brake Oil Pressure Switches
Dash Panel.
When the service brake is applied and service brake oil pressure rises above 200 ± 50 kPa (29 ± 7 psi), residual brake oil pressure switches (1) and (2) will close. Power will now be supplied to illuminate residual brake pressure light (3).
If service brake oil pressure in the front or rear brake circuit remains above 200 ± 50 kPa (29 ± 7 psi) after the service brakes have been released, the light will remain illuminated.
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If the residual brake pressure light stays on after the brakes have been released, stop the machine immediately. Engage the parking brake. Stop the engine. Do not operate the machine until the cause has been corrected. |
Towing Brake Release System
SMCS Code:4282
Tow Bar
Hydraulic Schematic for the Braking System
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The towing brake release system must only be activated by a towing hook securely attached to the recovery machine. The towing hook must be securely attached to the towing hitch of the disabled machine prior to activating the release system. Failure to do so may result in the disabled machine moving, causing serious personal injury or death. When the disabled machine has been towed to a safe place, ensure it is parked on a level surface and the wheels are blocked securely so that the machine can not move prior to any service work being performed on the machine. Ensure the disabled machine can not move before disconnecting the towing hook. |
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If the parking brake is engaged due to a machine fault and the machine must be towed, the towing brake release system can be used to release the machine brakes.
The towing brake release system can be activated by a towing hook compressing the piston in the towing brake release cylinder. The towing brake release cylinder is located in the machine towing hitch at the rear of the machine.
The towing brake release system consists of the following components: towing brake release cylinder (10), check valve (11), towing brake release sequence valve (12) and shuttle valve (18).
Rear of the machine
When the towing brake release system is activated, the piston in towing brake release cylinder (10) is forced upwards against a spring in the cylinder.
Left Side of the Torque Converter Compartment
Left Side of the Transmission Compartment
The hydraulic oil in the towing brake release cylinder is forced from the cylinder and directed through shuttle valve (18) to the wheel brakes. The oil pressure then releases the parking brake section of the wheel brakes.
When the towing brake release system is deactivated, the force on the piston in towing brake release cylinder (10) is removed. The spring in the towing brake release cylinder causes the piston to move downwards. The pressure of the hydraulic oil in the parking brake section of the wheel brakes is released and the oil flows back to towing brake release cylinder (10). The parking brake will now be engaged by the springs in the wheel brakes.
Towing brake release sequence valve (12) ensures that when the parking brake is disengaged during normal machine operation, the towing brake release system is disabled.
Recovery Hook
Hydraulic Schematic for the Braking System
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If the disabled machine is in a stope or dangerous area, the recovery machine must be operated by remote control. The towing brake release system must only be activated by a tow line securely attached to the recovery machine. The tow line must be securely attached to the recovery hook of the disabled machine prior to activating the release system. Failure to do so may result in the disabled machine moving, causing serious personal injury or death. When the disabled machine has been towed to a safe place, ensure it is parked on a level surface and the wheels are blocked securely so that the machine cannot move prior to any service work being performed on the machine. |
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If the parking brakes are applied due to a machine fault and the machine must be towed, the brake release system (recovery hook) can be used to release the machine brakes.
The towing brake release system is activated by an external force being applied to the recovery hook. The recovery hook is located on the towing hitch at the rear of the machine.
The towing brake release system consists of the following components: check valve (11), towing brake release sequence valve (12), shuttle valve (18), recovery hook (24).
Rear of the machine
Left Side of the Torque Converter Compartment
Left Side of the Transmission Compartment
When the towing brake release system is activated, recovery hook (24) compresses the piston in towing brake release cylinder (10) against spring pressure. The hydraulic oil in the towing brake release cylinder is forced from the cylinder and directed through shuttle valve (18) to the wheel brakes. The oil pressure then releases the parking brake section of the wheel brakes.
When the external force on recovery hook (24) is removed the towing brake release system is deactivated, and the piston in towing brake release cylinder (10) is returned by spring pressure. The hydraulic oil disengaging the parking brakes is now returned to towing brake release cylinder (10). The parking brakes will now be engaged.
Towing brake release sequence valve (12) ensures that when the engine is running, the towing brake release system is disabled.
Parking Brake Manual Release System
SMCS Code:4267; 7000
Auxiliary Brake Release Group
If the parking brake is engaged due to a machine fault and the machine must be towed, an optional auxiliary brake release group is available to disengage the parking brake. 1DE3048Portable Hydraulic Pump (1) is used to supply oil pressure to disengage the parking brake and to operate the service brakes.
Operator's Compartment
The portable hydraulic pump is activated by hand-held release switch (2) from the operator's compartment of the machine. The switch must be held on manually for the pump to stay activated.
When the switch is held in the ON position, the portable hydraulic pump supplies oil to the brake accumulator charging valve, the parking brake circuit and the STIC steering and hydraulic pilot circuits. The operation of the braking system is then the same as when the brake and pilot pump is used to supply oil to the brake system (as long as the switch is held on).
NOTE: Operation of the brake release switch should only take place from inside the operator's compartment.
Reference: For the correct procedure to manually release the parking brake, refer to Systems Operation, Testing and Adjusting, "Parking Brake - Manual Release" for the machine that is being serviced.