BENDIX TCH-013-002 User Manual

Technical Bulletin

Bulletin No.: TCH-013-002 Effective Date: 3/14/96 Cancels: NA Page: 1 of 1

Subject: M-21 and M-22 Modulator Interchange

There were two Bendix antilock modulators currently available from Bendix Commercial
Vehicle Systems, the older M-21 and the newer M-22. The new M-22 can be used to
replace the older M-21 with some minor mounting and wiring considerations.

When replacing an M-21 modulator with an M-22 modulator the following must be
considered during the installation process.

1. Study figures 1 & 2 and note where the exhaust port is located on both the M-21 and
M-22. The exhaust on both modulators must be directed toward the road surface
when mounted on the vehicle.

2. Note that the delivery port (to the brake chamber) for the M-21 is on the same side
as the electrical connector. The M-22 is exactly reverse of this with the delivery port
on the side opposite the electrical connector.
Note: The position of the Supply Port, Delivery Port, and Exhaust Port determine
how the modulator must be mounted NOT THE ELECTRICAL CONNECTOR.

3. In all cases the electrical wire harness must be rerouted, reconnected to the M-22
and securely fastened.
IMPORTANT: The wire harness must not be STRAINED. A two inch radius must be
maintained in the wire harness to assure it will not pull out of the connector or allow
water to enter the connector. Early issues can be expected if the wire harness does
not have adequate strain relief.

With these few cautions in mind the new M-22 can be used to replace the older M-21
modulator.