Bendix M-30 ANTILOCK MODULATOR ASSY User Manual
®
Bendix® M-30™ AntiLock Modulator Assembly
SD-13-4830
Supply Port
(cast in 1, SUP)
M-30™ Modulator
Delivery Port
(cast in 2, DEL)
Electrical Connector
Mounting Holes
(.33" diameter thru body)
Exhaust Port
(cast in 3, EXH)
FIGURE 1: M-30™ MODULATOR
Solenoid
Connector
Supply Port
(cast in 1)
Supply Port
Delivery Port
(cast in 2)
(cast in 1)
Solenoid
Connector
Mounting
Holes
Mounting
Holes
Exhaust
(cast in 3)
FIGURE 2: M-21™ MODULATOR FIGURE 3: M-22™ MODULATOR
DESCRIPTION
™
The Bendix® M-30™ modulator replaced both the M-21
(Figure 2) and M-22™ (Figure 3) modulators in all applications.
The M-30™ antilock system modulator (Figure 1) is a high
capacity , on/off air valve that incorporates a pair of electrical
solenoids for control. The solenoids provide the electropneumatic interface between the antilock controller
electronics and the air brake system. The modulator is
used to control the braking function on individual or dual
service actuators during antilock activity. When used to
control both service chambers on an axle or two chambers
on the same side of a tandem axle, the modulator is
sometimes mounted ahead of a quick release valve, which
provides quick exhaust of service applications during normal
braking (Figure 4). In the case of individual wheel control
applications, the modulator is always the last control valve
through which air passes on its way to the service brake
actuator.
The modulator consists of a die cast aluminum body and a
solenoid assembly which contains one normally open
solenoid, one normally closed solenoid, and an inlet and
exhaust diaphragm valve. A three pin, weather resistant
electrical connector is an integral part of the modulator
solenoid assembly and serves to carry control commands
from the antilock controller to the modulator. Two mounting
holes are provided for frame or cross member mounting of
the valve.
Delivery Port
(cast in 2)
Exhaust
(cast in 3)
1
FRONT AXLE SYSTEMS
REAR AXLE SYSTEM
WHEEL CONTROL
SERVICE
BRAKE
CHAMBER
TO ANTILOCK
CONTROLLER
MODULATOR
MODULATOR
ANTILOCK
CONTROLLER
SERVICE
BRAKE
CHAMBER
M-30
M-30
TO
WHEEL CONTROL WHEEL CONTROL
TO ANTILOCK
™
M-30
™
CONTROLLER
MODULATOR
OR
QUICK RELEASE VALVE
™
SERVICE
BRAKE
CHAMBER
™
M-30
MODULATOR
TO ANTILOCK
CONTROLLER
SERVICE
CHAMBER
AXLE
CONTROL
TO
ANTILOCK
CONTROLLER
OR
M-30™ MODULATOR
QUICK RELEASE VALVE
BRAKE
TO
ANTILOCK
CONTROLLER
TO
ANTILOCK
CONTROLLER
CONTROLLER/
SERVICE &
SPRING
BRAKE
CHAMBER
™
M-30
MODULATOR
RELAY
ASSEMBLY
™
M-30
MODULATOR
FIGURE 4: TYPICAL WHEEL AND AXLE CONTROL SYSTEMS
NOTE: USE OF A QUICK RELEASE VALVE IS NOT TYPICALLY REQUIRED WITH THE M-30™ MODULATOR. REFER TO VEHICLE SPECIFICATIONS FOR
RECOMMENDED CONFIGURATION.
™
The Supply, Delivery and Exhaust ports on the M-30
modulator are identified with a cast, embossed numeral for
positive identification.
Identification Air Line Connection
1, SUP Supply
exhaust diaphragm. Air pressure, along with spring force,
seats the exhaust diaphragm on the exhaust passage, thus
preventing the escape of service air. Simultaneously,
application air flows to the supply diaphragm and forces it
away from its seat. Air flows past the open supply port and
out the modulator delivery port to the service brake chambers.
(incoming air from foot, relay or quick release valve)
2, DEL Delivery
(air delivery to service actuators)
3, EX H Exhaust
NON ANTILOCK HOLD (FIGURE 6)
When the desired air pressure is attained in the service
brake chambers, the brake system is in the Holding position.
In the Holding position, both solenoids in the modulator
remain de-energized and the balance of the internal
FUNCTIONAL CHECK
A wiring harness connects the vehicle modulators to the
components remain in the same position as they assumed
during application.
controller. The ABS controller is able to simultaneously and
independently control the individual modulators. When
vehicle power is supplied to the ABS ECU, a modulator "chuf f"
test is performed. When the brake pedal is depressed and
the ignition turned on, the modulator "chuff" test can be
NON ANTILOCK EXHAUST
The manner in which air exhausts through the modulator
differs, depending upon how rapidly the brake application is
released by the driver.
heard. This test will verify if the modulator is functioning
pneumatically correct. The modulators will exhaust air in
the sequence of right front, left front, right rear , left rear. If
they do not follow this sequence, proceed with modulator
troubleshooting.
Normal Exhaust (Figure 7) - During a normal, relatively
"slow" brake release, air moves back through the modulator
in the reverse direction as it flowed during application. The
internal components of the modulator will remain in the same
position as they assumed during application until air pressure
OPERATION
decreases to approximately one half psi, at which time the
supply diaphragm will seat on the supply passage. A
NON ANTILOCK APPLICA TION (FIGURE 5)
During normal, non antilock braking, both solenoids are
relatively small amount of air will generally be expelled from
the modulator exhaust port during "slow" brake release.
de-energized (no electrical power). Brake application air
enters the Supply port of the modulator and flows to the
2
EXHAUST PORT
EXHAUST
DIAPHRAGM
EXHAUST
VALVE
BRAKE VALVE
SPRING
SUPPLY OR
BIAS
BRAKE
CHAMBER
FIGURE 5: M-30™ MODULATOR NON ANTILOCK APPLICATION OF SERVICE BRAKES
EXHAUST
PORT
VALVE
EXHAUST
DIAPHRAGM
HOLD
DIAPHRAGM
HOLD
VALVE
EXHAUST
VALVE
SPRINGSPRING
BRAKE
CHAMBER
FIGURE 6: M-30™ MODULATOR NON ANTILOCK APPLICATION HELD POSITION
BIAS
VALVE
BRAKE
VALVE
HOLD
VALVE
SUPPLY OR
HOLD
DIAPHRAGM
3
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