1
®
SD-13-4793
DESCRIPTION
There are two Bendix antilock modulators available from
Bendix Commercial Vehicle Systems LLC, the older M-21
™
modulator and the newer M-22
™
modulator. Both are
functionally the same.
The M-21
™
and M-22
™
antilock system modulators (Figure
1) are essentially high capacity, on/off air valves that
incorporate a pair of electrical solenoids for control. The
solenoids provide the electro-pneumatic interface or link
between the antilock controller electronics and the air brake
system. The modulator can be used to control the braking
function on an individual wheel or two service actuators. 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 2) 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 and a solenoid assembly which contains one
normally open solenoid (NOS), one normally closed solenoid
(NCS), and two inlet and exhaust diaphragm valves. A
Packard, three pin, 280 series 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, .35 inch diameter,
mounting holes are provided for frame or cross member
mounting. The single supply, delivery and exhaust port on
both modulators is identified with a cast, embossed numeral
for positive identification.
Bendix
®
M-21
™
and M-22
™
AntiLock Modulator Assembly
FIGURE 1 -
M-21
™
AND M-22
™
MODULATOR
M-21
™
MODULATOR
M-22
™
MODULATOR
SUPPLY
(CAST-IN ID #1)
SUPPLY
(CAST-IN ID #1)
DELIVERY
SUPPLY
MOUNTING
HOLES
DELIVERY
(CAST-IN ID #2)
SOLENOID
CONNECTOR
SUPPLY
DELIVERY
EXHAUST
(CAST-IN ID #3)
SOLENOID
CONNECTOR
MOUNTING
HOLES
DELIVERY
(CAST-IN ID #2)
EXHAUST
(CAST-IN ID #3)
