7 FRENOS Systems Operation

120G Motor Grader 4HD00001-UP (MACHINE) POWERED BY 3304 Engine(SEBP...
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Producto: MOTOR GRADER

Modelo: 120G MOTOR GRADER 4HD
Configuración: 120G Motor Grader 4HD00001-UP (MACHINE) POWERED BY 3304 Engine
Operación de Sistemas
120G, 130G & 140G MOTOR GRADER AIR SYSTEM & BRAKES
Número de medio -SENR3607-00 Fecha de publicación -01/03/1987 Fecha de actualización -11/10/2001
Systems Operation
SMCS - 1400
Introduction
Schematic Of Air System And Brakes With Two Section Air Tank And Dual Brake Control Valve
(1) Service brakes (four) (2) Tee (3) Junction block (4) Air compressor governor (5) Air compressor (6) One-way check valve (7)
Parking brake valve (8) Dual brake control valve for service brakes (9) Junction block (10) Air relief valve (11) One-way check
valve (12) Air warning pressure switches (13) Drain plugs (14) Air tank (15) One-way check valve (16) Air relief valve (17)
Rotochamber for parking brake (18) Quick release valve (19) Junction block (20) Air pressure gauges (21) Solenoid (22)
Centershift lock control valve (23) Stop light switch (24) Centershift lock (25) One-way check valve
Reference: For Specifications with illustrations, make reference to the Specifications for 120G, 130G and
140G Motor Graders Air System and Brakes, Form SENR3607. If the Specifications given in Form
SENR3607 are not the same as given in the Systems Operation and the Testing And Adjusting, look at the
printing date on the back cover of each book. Use the Specifications given in the book with the latest date.
https://sis.cat.com/sisweb/sisweb/techdoc/techdoc_print_page.jsp?returnurl=/sisweb/s... 30/05/2013
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120G Motor Grader 4HD00001-UP (MACHINE) POWERED BY 3304 Engine(SEBP... Page 2 of 15
If the TROUBLESHOOTING gives an indication of leakage through a control valve(s), disconnect the
delivery hose at the end opposite the delivery port (disconnect signal hoses when checking control valve for
service brakes). Put the end of the hose in a pan of water to check for leakage.
The brake system is activated by air pressure. Air compressor (5) sends pressure air to air tank (14) through
the one-way check valves (11) and (15). The air tank is divided into two separate sections. Each section has
a safety valve and a drain valve.
Pressure air goes from dual brake control valve (8) to activate the brakes. In case of a failure in a line or one
of the circuits, one section of the air tank will still have pressure air to engage the brakes on one drive
tandem.
Air Tank
(11) One-way check valve (14) Air tank (15) One-way check valve
Service Brakes
Four disc-type brakes, one in each wheel spindle housing, are used for the service brake system. The cooling
of the brakes is through the oil in the drive tandems. The service brakes are activated by air pressure.
Typical Example Gauge Panel

(20) Air pressure gauges
Air from both sections of air tank (14) goes to dual brake control valve (8) for the service brakes.
Control Valve For Service Brakes

(8) Dual brake control valve (23) Stoplight switch
Pushing the brake pedal on the dual brake control valve (8) sends an air signal to let part of the pressure air
from the air tank go to the brakes. The position of the brake pedal controls the amount of the air signal.
When the brake pedal is held in the brake ON position, dual brake control valve (8) stops the air signal to
the brakes. Pressure air is held in the brakes to keep the brakes in the brake ON position.
When the brake pedal is released the air signal is released through the dual brake control valve. With no air
signal in the lines to the brakes the brakes are released.
Parking Brake
A disc-type brake in the front part of the transmission housing is used as the parking brake. Rotochamber
(17) on the side of the transmission activates the brake. The parking brake is air released and spring
engaged.
Air from the dual brake control valve (8) goes through one-way check valve (6). When the parking brake
lever is pulled to the rear, pressure air goes through the parking brake valve (7).
Typical Example Rotochamber For Parking Brake

(17) Rotochamber
Air then goes through the quick release valve into rotochamber (17). The pressure air moves the rod and rod
end. The rod end is connected to a lever on the front of the transmission housing. This lever is connected to
the parking brake piston in the transmission. As the rotochamber moves the rod end and the lever down, the
piston is turned to release the disc-type brake. The one-way check valve prevents the parking brake from
engaging if air pressure to the control valve is low.
When the lever is pushed forward to the PARK position, the inlet port in valve (7) for the parking brake
closes and the exhaust port opens to release the air in the line to quick release valve (18). The exhaust port
of the quick release valve then opens to release the air in the rotochamber. With no pressure air in the
rotochamber, the spring force moves the rod and rod end out of the rotochamber. This moves the lever on
the transmission to engage the parking brake.
Lever For Parking Brake In Park Position
When the machine is stopped and the lever is pushed to the PARK position, the transmission shift lever is
held in the NEUTRAL position. In an emergency, when the machine is being operated, the lever can be
pushed to the PARK position.
This will engage the parking brake and also move the transmission shift lever to the NEUTRAL position.
Centershift Lock
The location of centershift lock (24) is on the front of the link bar. When the lock pin is not engaged with the
lock plate, the link bar and the circle can be moved to put the blade in the correct position for the job
application.
Typical Example Centershift Lock

(24) Centershift lock
Centershift control valve (22) is on the console to the right of the seat. This control valve controls the flow
of air to the lock pin. The machine is normally operated with the control valve in the LOCK position. Since
the lock pin can not be seen by the operator, indicators on the rear of the lock plate show the operator when
the lock pin is in alignment with the correct hole in the lock plate.
Centershift Indicators
Air from the dual brake control valve (8) goes to centershift control valve (22). In the LOCK position, air
goes through the valve to the spring side of the piston in the lock pin housing. The force of the springs and
the pressure air hold the lock pin in the LOCK position. In order to move the link bar and the circle to
another location, the lever on centershift control valve (22) first must be moved to the INDEX position. This
releases the air from the spring side of the piston. The lever is then moved to the RETRACT position.
Pressure air is sent to the other side of the piston to pull the lock pin out of the lock plate against the force of
the springs. The centershift cylinder and the lift cylinders are then operated to move the link bar and the
circle to the desired location. The one-way check valve (25) prevents the centershift lock from operating if
air pressure to control valve is low.
When the lock pin is near the correct hole in the lock plate, the lever on the control valve is moved back to
the INDEX position. This releases the pressure air holding the lock pin away from the lock plate. When the
lock pin is in alignment with the correct hole, the spring force will push the lock pin part of the way into the
lock plate. The lever on the centershift control valve is then moved to the LOCK position to again send
pressure air to the spring side of the piston. The spring force and the pressure air will then fully engage the
lock pin in the lock plate.
Control Lever For Centershift Control Valve
Electric Warning System

The warning system has three separate circuits. The main circuit has an electric buzzer and an indicator light
(26) for low air pressure. Two pressure switches (12), one on each section of dual brake control valve for
service brakes are connected to the buzzer and the indicator light. In case of a failure in either half of the air
system, one of the pressure switches will close at approximately 517 kPa (75 psi). This completes a circuit
to operate the buzzer and the indicator light. The operator can then safely stop the machine and look at air
pressure gauges (20) on the front of the engine compartment to see which part of the system has the failure.
NOTE: The electric buzzer is under the panel to the right of the seat.
Warning Lights
(26) Indicator light for service brakes
The last circuit is for the brake lights. A stoplight switch is in the line from dual brake control valve (8) for
service brakes to one of the lines to the brakes. When the foot pedal is pushed, the stoplight switch closes.
This completes a circuit to operate brake lights.
Each warning circuit is connected to the battery through a separate fuse in the fuse box.
Air Compressor And Governor

The engine operates air compressor (5) through the timing gears. The air compressor governor (4) controls
the system air pressure.
The governor keeps the air pressure in the system constant. When the engine is started, the compressor runs
until the pressure in the system is at the cutout setting of 930 ± 34 kPa (135 ± 5 psi). At this setting, pressure
air moves the governor piston to let air go through the governor to the unloading valves in the compressor.
Pressure air holds the unloading valves open to stop the flow of air from the compressor.
When the system air pressure is at the cut-in setting of 758 kPa (110 psi) min the force of the governor
spring moves the governor piston to stop the flow of air to the unloading valves. The unloading valves close
and the compressor again sends pressure air to the system.
Typical Example Air Compressor And Governor

(5) Air compressor (4) Air compressor governor

Right Brake Application
When the brake pedal is pushed, plunger (1) puts force on spring seat (3), rubber spring (4) and piston (5).
The seat (6) seats on inlet and exhaust valve (9) and closes exhaust passage (7). Inlet and exhaust valve (9)
is moved off seat (8) to let pressure air from supply port (11) go out delivery port (10) to the brakes for the
right side of the machine.
NOTE: Because of the small amount of pedal movement and air needed to move the relay piston (12), the
brakes for the left side of the machine are applied almost the same time, (almost simultaneous) as the brakes
for the right side of the machine.
Left Brake Application

When the inlet and exhaust valve (9) is moved off of its seat (8), exhaust seat (14) seats on inlet and exhaust
valve (20) and closes exhaust passage (15). Inlet and exhaust valve (20) is moved off seat (19) to let air from
supply port (17) go out delivery port (18) to the brakes for the left side of the machine.
Releasing the Brakes

When the brake pedal is released, mechanical force is removed from the spring seat (3), rubber spring (4)
and piston (5). Air pressure and spring force moves piston (5) which in turn moves relay piston (12) by way
of screw (2). Seat (6) is moved away from inlet and exhaust valve (9). Inlet and exhaust valve (9) moves
into contact with seat (8) and air pressure in the lines to the brakes for the right side of the machine goes
through the center of the valve and out the exhaust port (21) and the brakes for the right side of the machine
are released. At the same time, exhaust seat (14) moves away from inlet and exhaust valve (20) and inlet and
exhaust valve moves into contact with seat (19). Passage (15) is closed off to stop air flow from supply port
(17) to delivery port (18). Air pressure in the lines to the bakes for the left side of the machine goes through
the center of the inlet and exhaust valve (20) and out the exhaust port (21) and the brakes for the left side of
the machine are released.
Loss of Brakes for Left Side

Should air pressure in the circuit for the brakes on the left side of the machine be lost, the circuit for the
brakes on the right side of the machine will still provide for brakes on the right side of the machine.

(1) Plunger (2) Screw (3) Spring seat (4) Rubber spring (5) Piston (6) Seat (7) Exhaust passage (8) Seat (9) Inlet and exhaust
valve (10) Delivery port (11) Supply port (12) Relay piston (13) Spring (14) Exhaust seat (15) Exhaust passage (16) Spring (17)
Supply port (18) Delivery port (19) Seat (20) Inlet and exhaust valve (21) Exhaust port
Loss of Brakes for Right Side

Should air pressure in the circuit for the brakes on the right side of the machine be lost, the brakes for the
left side of the machine can still be applied. As the brake pedal is pushed, and there is no air pressure at
supply port (11) and delivery port (10), there will be no brakes for the right side of the machine. Piston (5)
will mechanically move relay piston (12) to close inlet and exhaust valve (20) and let air pressure from
supply port (17) go out delivery port (18) to the brakes for the left side of the machine.
Brakes Balanced (Right Side)

When the air pressure at the delivery port (10) is the same as the mechanical force of the brake pedal, piston
(5) will move and the inlet and exhaust valve (9) will close and stop the flow of air from supply port (11).
The inlet and exhaust valve (20) will stay closed and will not let air pressure go out through exhaust port
(21).
Brakes Balanced (Left Side)

When the air pressure under relay piston (12) is near the air pressure on top of it, the relay piston (12) moves
to close the passage (15) and stops the flow of air from supply port (17) to delivery port (18). Exhaust port
(21) will stay closed as the air pressure for the brakes on the left side of the machine becomes the same as
the air pressure for the brakes on the right side of the machine.
When brake applications are made gradual, a balance position in the section for the brakes on the right side
of the machine is reached when the air pressure at the delivery port (10) is the same as the pressure of the
operator's foot on the pedal. A balance position is reached in the section for the brakes on the left side of the
machine when the air pressure under the relay piston (12) gets close (approaches) the air pressure above the
relay piston (12).
When the brake pedal is pushed all the way down, both the inlet and exhaust valves (9) and (20) are open
and full air pressure for the air tanks go to the brakes for both sides of the machine.
Service Brakes
The power from the differential is through drive chain (3) to sprocket (1). The sprocket turns wheel spindle
(5), hub (2) and discs (8) in wheel spindle housing (13). The drive wheels are connected to flange (14) of
wheel spindle (5).
The disc-type brakes, one in each wheel spindle housing, are operated by air pressure from the service brake
control valve. Each brake is made up of discs (7) connected to spindle housing (13) and discs (8) connected
to hub (2). The cooling of the brakes is through the oil in the drive tandems.
Pressure air goes through port (10) into air compartment (9). Air then moves piston (11) against discs (7)
and (8). The piston pushes the discs against cover (6). As the air pressure becomes higher, the force of
piston (11) pushing against the discs causes friction between the discs. As the friction becomes greater, discs
(8), hub (2) and wheel spindle (5) will start to slow down, since discs (7) and wheel spindle housing (13)
cannot turn. This is the brake ON position, but the brakes are not fully engaged.
If the operator pushes the foot brake pedal down completely, the control valve for the service brakes will
send a large air signal to let the air pressure in air compartment (9) become higher. The friction between
discs will then become great enough to stop discs (8), hub (2) and wheel spindle (5).
Typical Example Service Brakes

(1) Sprocket (2) Hub (3) Drive chain (4) Shims (5) Wheel spindle (6) Cover (7) Discs (connected to spindle housing) (8) Discs
(connected to hub) (9) Air compartment (10) Inlet port (11) Piston (12) Spring (13) Wheel spindle housing (14) Flange (part of
wheel spindle)
Wheel Spindle Housing

(10) Inlet port (13) Wheel spindle housing
When the operator releases the foot brake pedal, the pressure air in air compartment (9) is released through
port (10) to the exhaust port in the relay valves. Spring (12) then pushes piston (11) back to the brake OFF
position. Discs (8) are again free to turn between discs (7).
120G Motor Grader 4HD00001-UP (MACHINE) POWERED BY 3304 Engine(SE... Page 10 of 15
Control Valve For Parking Brake

The location of the control valve for the parking brake is under the console for the transmission shift lever.
The safety lever between slots for the transmission shift lever operates the control valve.
Control Valve For Parking Brake

(1) Piston (2) Stem (3) Chamfer on stem (4) Spring (5) Supply port (6) Exhaust port (7) Delivery port
The flow of air is through a one-way check valve to supply port (5). When the parking brake lever is pulled
to the rear of its slot, piston (1) is moved into the control valve. The piston pushes stem (2) down to open a
passage from supply port (5) to delivery port (7). Chamfer (3) closes the opening from delivery port (7) to
exhaust port (6). Pressure air goes through the control valve through the quick release valve to the
rotochamber. Pressure air in the rotochamber then releases the parking brake.
When the lever is pushed to the PARK position, spring (4) moves stem (2) and piston (1) up to stop the flow
of air to delivery port (7). This opens the passage from the delivery port to exhaust port (6). Air in the line to
the quick release valve is released through the exhaust port. Pressure air in the rotochamber is then released
through the quick release valve. The spring in the rotochamber can then engage the parking brake.
Quick Release Valve

The quick release valve is connected to the inlet port of the rotochamber for the parking brake. The line
from the delivery port of the control valve for the parking brake is connected to inlet port (4) on the quick
release valve.
The quick release valve is used to shorten the time needed to release the parking brake. It is used to let the
air out of the brake chamber sooner. Air is released through the exhaust port (7) in the quick release valve so
it does not have to go back to the control valve for the parking brake to get out.
Operation
The quick release valve has three normal positions during operation. These positions are the
APPLICATION position (when air under pressure goes through the valve into the brake chamber), the
HOLD position (when pressure is kept in the brake chamber) and the EXHAUST position (when air in brake
chamber is being let out).
Quick Release Valve In Applied Position

(1) Outlet port to brake chamber (2) O-ring seal (3) Cover (4) Inlet port (5) Diaphragm (6) Body (7) Exhaust port (8) Plug
When the brake control valve is opened, air under pressure enters inlet port (4) of quick release valve and
moves diaphragm (5) down, to close exhaust port (7). The outer edges of the diaphragm are deflected
downward allowing air under pressure to pass through outlet port (1) to brake chamber, applying the brake.
One quick release valve is shown. On the left valve, plug (8) is in opposite brake port.
Quick Release Valve In Hold Position
As soon as brake chamber pressure below the diaphragm is equal to brake valve pressure above the
diaphragm, the edge of the diaphragm (5) moves up against the body. The center of the diaphragm continues
to cover exhaust port (7). This is the HOLDING position.
Quick Release Valve In Exhaust Position
When brake control valve is CLOSED, line pressure on top of diaphragm is released. The brake chamber
pressure below center of the diaphragm raises it, opening exhaust port (7) and permitting brake chamber air
to be released to atmosphere.
The diaphragm again assumes HOLDING position as soon as pressure above and below it is equalized.
Use a nonflammable cleaning solvent to clean any accumulations of grease and dirt from the area of the
quick release valve.
Disassemble quick release valve and inspect diaphragm (5) for wear or cracking. Contact surface of the
diaphragm should be free of pits or grooves.
Inspect seats on body (6) and cover (3).
Parking Brake
The location of the parking brake is around the No. 7 clutch in the planetary group of the transmission. The
parking brake is made up of piston (1), plates (4) and discs (5). Discs (5) are connected to ring gear (8) of
the No. 7 clutch. Plates (4) are connected to housing (6) by pins and can not turn. Ring gear (8) is connected
to the pinion in the differential. Lever (11) is connected to another lever inside of the transmission housing.
This lever fits in a slot in piston (1).
In the PARK position, no pressure air is available to rotochamber (12). The spring in the rotochamber will
move lever (11) up. This causes the lever inside of the transmission to turn piston (1). As the piston turns,
balls (10) move up the taper of inserts (9). The piston is moved into contact with plates (4) and discs (5).
The piston pushes the plates and discs against housing (6). As the friction between the plates and discs
becomes greater, ring gear (8) is stopped. Since the ring gear is connected to the pinion in the differential
through output flange (7), the machine can not move.
Parking Brake In Planetary Group Of Transmission

(1) Piston (2) Plunger (3) Spring (4) Plates (5) Discs (6) Housing (7) Output flange (8) Ring gear of No. 7 clutch (9) Inserts (10)
Balls
When the control lever is moved to the brake OFF position, pressure air is available to rotochamber (12).
The pressure air, working against the force of the spring in the rotochamber, will move the lever (11) down.
This causes the lever inside of the transmission to move piston (1) away from plates (4) and discs (5). Discs
(5) are then free to rotate with ring gear (8).
Lever To Parking Brake

(11) Lever (12) Rotochamber
Rotochamber For Parking Brake

When the safety lever is pushed to the PARK position, pressure air in air compartment (3) is released
through port (5) to the exhaust port in the quick release valve. Spring (1) then moves piston (2), sleeve (4)
and rod (7) to the right. A rod end on rod (7) is connected to the parking brake lever on the side of the
transmission. As rod (7) moves out of housing (6), the parking brake lever is moved to engage the parking
brake.
When the lever is pulled to the brake OFF position, pressure air goes through port (5) to air compartment
(3). The pressure air moves piston (2), sleeve (4) and rod (7) back to the left. Rod (7) then moves the
parking brake lever to release the parking brake.
Brake Off Position

(1) Spring (2) Piston (3) Air compartment (4) Sleeve (5) Port from quick release valve (6) Housing (7) Rod
Centershift Control Valve

Pressure air goes through supply port (17) of the centershift control valve to the spring side of valve (13).
The pressure air then goes around housing (21) to the spring side of valve (15). In the INDEX position, no
pressure air is available to either delivery ports (11) or (12). The delivery ports are open to the exhaust ports
through passages (19) and (22) in pistons (5) and (6). Detent (2) holds lever (1) in the correct position.
In the RETRACT position, lever (1) is pushed forward. Ear (4) on the lever turns to move piston (5) down.
When piston (5) comes into contact with valve (13), the opening to exhaust port (7) is closed. The piston
then moves valve (13) off its seat. This opens a passage to let pressure air from the supply port go around
valve (13) to delivery port (11). Pressure air then goes out delivery port (11) to the centershift lock pin to
push the pin out of the lock plate. Delivery port (12) is still open to exhaust port (8) through passage (22) in
piston (6). Detent (2) holds the lever in the correct position.
Centershift Control Valve Index Position

(1) Lever (2) Detent (3) Ear (4) Ear (5) Piston (6) Piston (7) Exhaust port (8) Exhaust port (9) Spring (10) Spring (11) Delivery
port (12) Delivery port (13) Valve (14) Spring (15) Valve (16) Spring (17) Supply port (18) Plug (19) Passage in piston (5) (20)
Spring (21) Housing for detent (22) Passage in piston (6)
From the RETRACT position, lever (1) is first moved back to the INDEX position. This releases this
pressure in delivery port (11) through exhaust port (7) when piston (5) moves back to its original position.
The lever is then pulled to the LOCK position. Ear (3) on the lever turns to move piston (6) down. Delivery
port (12) is then opened to the supply port in the same way as delivery port (11) in the RETRACT position.
Pressure air goes out delivery port (12) to push the lock pin back into the lock plate. In this position delivery
port (11) is open to exhaust port (7) through passage (19) in piston (5). Detent (2) will also hold the lever in
this position.
Centershift Lock Pin
Centershift Lock Pin Lock Position

(1) Lock pin (2) Link bar (3) Piston (4) Spring (5) Housing for piston (6) Bolts (7) Housing for spring (8) Port to lock pin side of
piston (9) Port to spring side of piston
In the LOCK position, pressure air from the centershift control valve goes through port (9) to the spring side
of piston (3). The pressure air helps spring (4) engage lock pin (1) in the lock plate.
To push the lock pin out of the lock plate, the centershift control valve is first moved to the INDEX position.
This releases the pressure air in port (9) through the control valve. The control valve is then moved to the
RETRACT position. Pressure air from the control valve is then sent through port (8) to the lock pin side of
piston (3). The pressure air has enough force to push the lock pin out of the lock plate against the force of
spring (4).
Copyright 1993 - 2013 Caterpillar Inc. Thu May 30 17:25:42 EST 2013
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Red privada para licenciados del SIS.

7 FRENOS Systems Operation

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120G Motor Grader 4HD00001-UP (MACHINE) POWERED BY 3304 Engine(SEBP...

Producto: MOTOR GRADER

Typical Example Gauge Panel

Control Valve For Service Brakes

Typical Example Rotochamber For Parking Brake

Lever For Parking Brake In Park Position

Typical Example Centershift Lock

Control Lever For Centershift Control Valve

Electric Warning System

Air Compressor And Governor

Typical Example Air Compressor And Governor

Control Valve For Service Brakes

Left Brake Application

Releasing the Brakes

Loss of Brakes for Left Side

Control Valve For Service Brakes

Loss of Brakes for Right Side

Brakes Balanced (Right Side)

Brakes Balanced (Left Side)

Typical Example Service Brakes

Wheel Spindle Housing

Control Valve For Parking Brake

Control Valve For Parking Brake

Quick Release Valve

Quick Release Valve In Applied Position

Quick Release Valve In Hold Position

Quick Release Valve In Exhaust Position

Inspect seats on body (6) and cover (3).

Parking Brake In Planetary Group Of Transmission

Lever To Parking Brake

Rotochamber For Parking Brake

Brake Off Position

Centershift Control Valve

Centershift Control Valve Index Position

Centershift Lock Pin

Centershift Lock Pin Lock Position

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