Bendix M-12-M-12R ANTILOCK MODULATOR User Manual
®
Bendix® M-12™ & M-12R™ AntiLock Modulator
4 PIN
CONNECTOR
SUPPLY
PORT DELIVERY
PORTS
2 VERTICAL
2 HORIZONTAL
CONTROL
PORT
COVER
PLATE
DELIVERY
PORTS
4 VERTICAL
WIRE
HARNESS
3 PIN
CONNECTOR
SD-13-4772
SUPPLY
PORT
CONTROL
PORT
M-12™ Modulator
FIGURE 1 M-12™ AND M-12R™ MODULATORS
DESCRIPTION
The M-12™ antilock modulator is a standard component in
Bendix antilock systems. It is comprised of two components:
solenoids, which rapidly apply and exhaust air during an
antilock stop, and a standard relay valve.
During normal, non-antilock operation, the M-12™ modulator
serves as a relay valve that speeds the application and release
of the service brakes. If wheel lock up is impending, a antilock
controller commands the solenoids to modulate brake
chamber pressure on the axle(s) on which the system is
installed.
The M-12™ modulator is offered in two configurations as
illustrated in figure 1. The M-12™ modulator permits direct
attachment of an antilock controller, and it accepts electronic
commands from the controller through a four pin connector
(see Figure 1). The M-12R™ modulator is designed for remote
mounting on a vehicle frame rail or cross member. It accepts
electronic commands from a remote mounted controller
through a wire harness assembly that has a four pin
connector at one end and a three pin connector at the other
(see Figure 1). The M-12™ modulator and M-12R™ modulator
differ from each other only in that the M-12™ modulator is
M-12R™ Modulator
designed for direct controller mounting while the M-12R
modulator uses a cover plate where the controller would
normally mount and a wire harness is attached to the
M-12R™ modulator in order to connect it to the antilock
controller. Two body styles are available; one with four
vertical delivery ports and another with two vertical and two
horizontal delivery ports.
The M-12™/M-12R™ modulator is normally mounted close
to the service actuators it serves, and it can be nipple
mounted to a reservoir or secured to the frame rail.
The M-12™ modulator air connections are as follows:
M-12™/M-12R™ Modulator Embossed
Air Connection Identification
Supply (to reservoir) SUP
Delivery (to brake actuator) DEL
(can have 2 horizontal & 2
vertical deliveries or
4 vertical deliveries)
Control CON
(to rear service brake valve delivery)
The standard M-12™ and M-12R™ modulator is offered with
a 4 psi crack pressure. The internal components are
interchangeable with R-12™ and R-14™ relay valves therefore,
the same maintenance kit is used to service all.
™
1
SERVICE
BRAKE
DASH
LAMP
SERIAL LINK
RELAY
SPRING
BRAKES
RETARDER
™
DISABLE
M-21
/M-22
™
MODULATOR
BRAKE VALVE
STOP LIGHT
SWITCH
M-12
MODULATOR
WITH ANTILOCK
CONTROLLER
MOUNTED
NOTCHED HUB
™
WHEEL
WS-20
SPEED SENSOR
EXCITER
FRONT AXLE
FIGURE 2A FULL VEHICLE AXLE CONTROL - TRUCK/TRACTOR
NOTCHED HUB
EXCITER
IN-AXLE WHEEL
SPEED SENSOR
™
REAR AXLE (S)
SPRING
BRAKES
™
WS-20
SPEED SENSOR
WHEEL
M-12R
™
MODULATOR
SR-5™ TRAILER
SPRING BRAKE
VALVE
FIGURE 2B TANDEM SPREAD AXLE TRAILER - AXLE CONTROL SYSTEM
2
REMOTE MOUNT
ANTILOCK
CONTROLLER
EXHAUST
SOLENOID
DOUBLE
CHECK
TRAILER
CONTROL
BRAKE
VALVE
SUPPLY
SOLENOID
RESERVOIR
SUPPLY
EXHAUST
FIGURE 3 APPLYING: NORMAL SERVICE APPLICATION
Figure 2 shows two antilock systems in which the M-12
and M-12R™ modulator can be used. Figure 2A is a typical
schematic for a full vehicle axle control system, and Figure
2B is a typical trailer installation using the M-12R
modulator. With the attachment of different controllers, the
M-12™ or M-12R™ modulator can adapt to either system.
OPERATION
APPLYING: NORMAL SERVICE APPLICATION
When a normal service brake application is made, and the
antilock wheel sensors do not sense impending wheel lock
up, service air pressure enters the modulator control port.
Air passes through the normally-open supply solenoid and
into the relay valve portion of the modulator. (The normallyclosed exhaust solenoid remains closed.)
Air acts on the relay piston closing the exhaust and opening
the inlet. Supply air pressure flows to the delivery ports and
out to the service brake chambers.
BALANCED POSITION: NORMAL SERVICE
APPLICATION
The relay valve portion of the modulator reaches a balanced
position when service delivery pressure acting on the
underside of the relay piston approaches that of the control
air acting on the top side of the piston. The piston moves
allowing the inlet valve to close, while the exhaust remains
closed. This prevents the valve from delivering or exhausting
air.
CONTROL
PISTON
DELIVERY
SERVICE BRAKE
CHAMBER
™
EXHAUSTING: NORMAL SERVICE
APPLICATION
When a service application is released, air at the modulator
™
control port returns to the application valve. Control pressure
above the relay piston exhausts through the supply solenoid
and the check valve in the solenoid housing out to the exhaust
port of the valve that sent the control signal. Relay piston
movement opens the modulator's exhaust, allowing air from
the piston's underside (and from the service brake chambers)
to exhaust through the modulator exhaust port.
ANTILOCK MODE: SOLENOIDS ACTIVATED
If a service application is made and the antilock controller
senses impending wheel lockup, it commands the M-12™/
M-12R™ modulator to modify the service brake application
pressure. When activated by the controller, the M-12™/
M-12R™ modulator solenoids alter application by exhausting
and applying control air pressure above the relay piston.
The supply solenoid closes, preventing control line pressure
from entering the modulator. Then the exhaust solenoid
opens, allowing control pressure to exhaust from the top
side of the piston through the exhaust port of the solenoid
assembly. This activity occurs in a pulsating manner,
simulating "pumping the brakes."
3
DOUBLE
CHECK
EXHAUST
SOLENOID
SUPPLY
SOLENOID
RESERVOIR
SUPPLY
EXHAUST
FIGURE 4 BALANCED POSITION
PREVENTIVE MAINTENANCE
Important: Review the warranty policy before performing
any intrusive maintenance procedures. An extended warranty
may be voided if intrusive maintenance is performed during
this period.
TRAILER
BRAKE
VALVE
CONTROL
PISTON
DELIVERY
SERVICE BRAKE
CHAMBER
CONTROL
2. Inspect all air lines connected to the M-12™/M-12R
modulator for signs of wear or physical damage. Replace
as necessary.
3. Test air line fittings for excessive leakage and tighten or
replace as necessary.
™
Because no two vehicles operate under identical conditions,
maintenance intervals will vary. Experience is a valuable guide
in determining the best maintenance interval for a vehicle.
GENERAL
Perform the following tests and inspections at the prescribed
intervals. If the M-12™/M-12R™ modulator fails to function as
described, or if leakage is excessive, repair the valve or obtain
a replacement from any authorized Bendix parts outlet.
EVERY THREE MONTHS, 25,000 MILES, 900 OPERATING
HOURS, OR DURING THE VEHICLE CHASSIS
LUBRICATION INTERVAL, MAKE THE VISUAL
INSPECTIONS IN THE SERVICE CHECKS
EVERY YEAR, 100,000 MILES, OR 3,600 OPERATING
HOURS, PERFORM THE OPERATIONAL AND LEAKAGE
TESTS
SERVICE CHECKS
1. Remove any contaminants and visually inspect the valve's
exterior for excessive corrosion or physical damage.
OPERATIONAL AND LEAKAGE TEST
OPERATIONAL TEST
1. Apply and release the brakes several times and check
for prompt application and release at each wheel. If the
response at the wheels is "sluggish," check for a kinked
or obstructed air line leading to or from the M-12™/
M-12R™ modulator.
2. Road test the vehicle to determine proper modulator
operation. The system can be tested by making an
aggressive stop from a vehicle speed of 20 mph. When
an aggressive stop is made, solenoid pulsation creates
an audible burst of air, which can be heard from outside
the vehicle.
LEAKAGE TEST
1. Build air system pressure to governor cut out. With the
service brakes fully applied, coat the exhaust port with
a soap solution. A 1" bubble in 3 seconds is permitted.
Coat the outside of the modulator body to check for seal
ring leakage. No leakage is permitted.
4
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