SD-13-4793, Description | BENDIX BW1664 instruction

SD-13-4793

Bendix® M-21™and M-22™AntiLock Modulator Assembly

SUPPLY

SOLENOID

CONNECTOR

	SUPPLY
DELIVERY
(CAST-IN ID #2)
			DELIVERY
			(CAST-IN ID #2)
		EXHAUST
		(CAST-IN ID #3)
		SUPPLY	DELIVERY
		(CAST-IN ID #1)
DELIVERY	SUPPLY
	(CAST-IN ID #1)	SOLENOID
		CONNECTOR
MOUNTING
HOLES			MOUNTING
			HOLES
	EXHAUST
M-21™MODULATOR	(CAST-IN ID #3)		M-22™MODULATOR
M-21™MODULATOR			M-22™MODULATOR

FIGURE 1 - M-21™AND M-22™MODULATOR

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.