Bendix MC-12 MODULATOR CONTROLLER ASSY User Manual

Bendix® MC-12™ Modulator Controller Assembly

SD-13-4762

™

EC-12

CONTROLLER

™

M-12

MODULATOR

DELIVERY

PORTS

(4 VERTICAL)

FIGURE 1 - MC-12™ MODULATOR CONTROLLER ASSY.

DIAGNOSTIC

DISPLAY

DESCRIPTION

The Bendix® MC-12™ modulator trailer antilock system is designed to improve vehicle stability by reducing wheel lock up during aggressive braking. Like Bendix's tractor antilock, the trailer system can provide single or tandem axle control. The main component is nipple mounted to a reservoir, so the system requires no special trailer modifications.

The trailer antilock system consists of the following: MC-12 modulator/controller, WS-20™ wheel speed sensors, electrical connectors and wiring. The MC-12™ modulator is the main component. It houses the EC-12™ electronic controller and the M-12™ modulator, which cont ains solenoids and a standard relay valve.

The EC-12™ controller houses the electronics that regulate the trailer antilock system and also incorporates a diagnostic display window and a 14 pin connector.

DIAGNOSTIC

DISPLAY

DELIVERY

14 PIN

CONNECTOR

CONTROL

PORT

(2 VERTICAL

HORIZONTAL)

wheel end send wheel speed information to the EC-12 controller through the 14 pin connector. The sensors are actually AC. generators. They house magnets, which create a magnetic field. When the field is interrupted by an irregular surface, such as a tone ring, AC. volt age is produced. The frequency of voltage increases or decreases as wheel speed increases or decreases.

During normal, non antilock operation, the M-12™ modulator's inlet solenoid is open, and the exhaust solenoid is closed.

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In this condition, the M-12™ modulator functions as a regular R-12™ relay valve. It receives a control signal from the foot valve, which passes through the open inlet solenoid and causes the brakes to apply in proportion to the amount of control pressure.

If wheel lock up is impending, the EC-12™ controller commands the solenoids to modulate brake chamber pressure on the axle(s) in which the system is installed.

PORTS

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The EC-12™ controller mounts to the M-12™ modulator with four bolts, and it is internally connected to the solenoids by a four pin connector. The solenoids are the interface between the EC-12™ controller electronic signals and the pneumatically operated modulator. Sensors mounted at the

The MC-12™ modulator/controller receives its power from the vehicle's stop light circuit (pin 4 on the standard seven pin connector—red). The power enters the EC-12™ controller at pin A and (optionally) pin B from the auxiliary terminal (blue wire) of the trailer’s 7 pin connector.

Seven Conductor Antilock Wire Gauge

Pin (Wire Connector Wire Single/

Connector No.) Letter Color Lamp and Signal Circuits Dolly Double Triple

1 1 C White Ground Return To Towing Vehicle 12 10 8 2 2 - Black Clearance, Side Marker and Identification Lamps 12 12 12 3 3 - Yellow Left Hand Turn Signal and Hazard Signal Lamps 12 12 12 4 4 - Red Stop Lamps 10 10 10 5 5 - Green Right Hand Turn Signal and Hazard Signal Lamps 12 12 12 6 6 - Brown Tail, Clearance, Side Marker and License Plate Lamps 12 12 12 7 7 B* Blue Auxiliary, Dome, Etc. or constant Antilock power 12 12 12 4 9 A Red Antilock Power From Stop Lamp 10 10 10

- 8 D Yellow Trailer Mounted Status Light 14/16 14/16 14/16

- 10/11 N/P - Wheel Speed Sensor 16/18 16/18 16/18

- 12/13 M/L - Wheel Speed Sensor 16/18 16/18 16/18

* Antilock Connector Pin B is an option and is used to provide constant power to the MC-12™ modulator during trailer operation.

CI/Directional

Stop & Tail

License Plate

The relay illustrated to the right is used when a tractor, dash mounted status lamp for the trailer antilock system is desired. Like the trailer mounted status lamp, this is an option and is not required.

Marker

MC-12

Wheel Speed

Sensor

To Pin “G” on

™

Modulator

Connector

To Power Side of

Tractor Ignition

Tractor Electrical

Relay

Tractor Dash Mounted Trailer Antilock Status

Lamp

Trailer

Mounted

Status

Marker Marker

Indicator

Clearance

Stop & Tail

CI/Directional

Marker

Rear 7 Pin Connector

Plug (See

Note)

Wheel Speed

Sensor

Note:

The rear 7 pin connector plug is for Dolly operations for Doubles & Triples

FIGURE 2 - MC-12™ MODULATOR TRAILER SYSTEM WIRING SCHEMATIC

Clearance

Marker Marker

System ground (pin 1 on the seven pin connector—white) enters the MC-12™ modulator at pin C.

Each wheel speed sensor sends the MC-12™ modulator its AC. signal through a pair of wires. The MC-12™ modulator pins for the sensors are L-M and N-P.

directs the driver to the problem area. A series of LEDs on the EC-12™ controller indicate the status of power, EC-12 controller, wheel speed sensors, M-12™ modulator solenoids, or voltage level.

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The MC-12™ modulator can send a +12v failure signal to the optional trailer mounted status light through pin D. The status light indicates the condition of the trailer antilock system. In addition, the MC-12™ modulator can send a grounding signal through its pin J to an optional tractor, dash mounted st atus lamp. During start up, when the trailer brakes are actuated, trailer antilock immediately runs a self check. The status light flashes once and then goes off. Should a problem occur , the antilock system disengages and returns to normal R-12™ relay valve operation.

If the status light comes on and remains on when the trailer brakes are actuated, a system problem has occurred. The EC-12™ controller contains a diagnostic window, which

EXHAUST SOLENOID

SUPPLY

SOLENOID

PEAK TO PEAK

LOW SPEED

PEAK TO PEAK

HIGH SPEED

FIGURE 3 - SPEED SENSOR VOL TAGE CYCLE OUTPUT

DOUBLE

CHECK

TRAILER

CONTROL

BRAKE

VALVE CONTROL

SUPPLY

EXHAUST

FIGURE 4 - APPLYING: NORMAL SERVICE APPLICATION

OPERATION

APPLYING: Normal Service Application

When a normal service brake application is made, and the EC-12™ controller does not sense impending wheel lock up, control air pressure from the brake valve enters the modulator

PISTON

DELIVERY

SERVICE

BRAKE

CHAMBER

control port. The air passes through the supply solenoid and acts on the modulator's piston. The piston closes the modulator exhaust and opens the inlet, delivering supply air out the delivery ports.

DOUBLE

CHECK

EXHAUST SOLENOID

SUPPLY

SOLENOID

SUPPLY

EXHAUST

FIGURE 5 - BALANCED POSITION: NORMAL SERVICE APPLICATION

BRAKE

VALVE

CONTROL

PISTON

DELIVERY

TRAILER

CONTROL

SERVICE BRAKE

CHAMBER

BALANCED POSITION: Normal Service Application

The modulator reaches a balanced position when control pressure acting upon the top side of the piston approaches that of the air acting upon the underside of the piston. The piston moves upward and closes the inlet valve, while the exhaust remains closed. This prevents the modulator from delivering or exhausting air.

EXHAUSTING: Normal Service Application

When the brake valve is released, control pressure exhausts through the supply solenoid and the check valve in the solenoid housing and out the exhaust port of the brake valve. As the piston moves upward, the modulator's exhaust opens, allowing air from the piston's underside to exhaust through the modulator exhaust port.

ANTILOCK MODE: Solenoids Activated

If a service brake application is made and the EC-12 controller senses wheel lockup, it will command the antilock system to alter the service brake application.

When activated, shuttles within the solenoids alter the application and exhaust of control air pressure. 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 of the brakes."

PREVENTIVE MAINTENANCE

1. Every 3 months; 25,000 miles; or 900 operating hours perform SERVICE CHECKS.

2. Every twelve months; 100,000 miles; or 3600 operating hours, disassemble the relay valve portion of the M-12 Modulator and clean parts with mineral spirits. DO NOT DISASSEMBLE THE SOLENOID ASSEMBL Y . Replace all rubber parts and any parts worn or damaged. Check

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for proper operation before placing vehicle in service.

EXHAUST SOLENOID

DOUBLE

CHECK

TRAILER

CONTROL

BRAKE

VALVE

SUPPLY

SOLENOID

SUPPLY

EXHAUST

FIGURE 6 - EXHAUSTING: NORMAL SERVICE APPLICATION

CONTROL

PISTON

DELIVERY

SERVICE BRAKE

CHAMBER

DOUBLE

CHECK

EXHAUST SOLENOID

SUPPLY

SOLENOID

SUPPLY

EXHAUST

TRAILER

CONTROL

BRAKE

VALVE

CONTROL

PISTON

DELIVERY

SERVICE BRAKE

CHAMBER

FIGURE 7 - ANTILOCK MODE: SOLENOIDS ACTIVATED

SERVICE CHECKS

Ensure that all wiring and connectors are secure and free from visible damage. Although the MC-12™ modulator assembly contains self check diagnostics, the LED (Light Emitting Diode) display should be inspected to ensure that the LEDs are functional. With the trailer brakes actuated, a magnet (800 gauss; capable of picking up 3 ounces) held to the LED reset area should cause all of the LEDs to illuminate. If one or more of the LEDs DO NOT ILLUMINA TE and the optional status light indicates proper system function, the non illuminated LED(s) should be noted for future reference. Although the diagnostic capabilities will be limited, the system will continue to function as designed.

The MC-12™ modulator assembly monitors the electronics of the system upon initial trailer brake application. However, the vehicle should be road tested periodically to verify proper solenoid function. The solenoids can be tested by making an aggressive trailer stop from a speed of 20 m.p.h. When an antilock stop is made, solenoid pulsation creates an audible burst of air, which can be heard from the out side of the trailer.

WARNING! PLEASE READ AND FOLLOW THESE INSTRUCTIONS TO AVOID PERSONAL INJURY OR DEATH:

When working on or around a vehicle, the following general precautions should be observed at all times.

1. Park the vehicle on a level surface, apply the parking brakes, and always block the wheels. Always wear safety glasses.

2. Stop the engine and remove ignition key when working under or around the vehicle. When working in the engine compartment, the engine should be shut off and the ignition key should be removed. Where circumstances require that the

engine be in operation, EXTREME CAUTION should be used to prevent personal injury resulting from contact with moving, rotating, leaking, heated or electrically charged components.

3. Do not attempt to install, remove, disassemble or assemble a component until you have read and thoroughly understand the recommended procedures. Use only the proper tools and observe all precautions pertaining to use of those tools.

4. If the work is being performed on the vehicle’s air brake system, or any auxiliary pressurized air systems, make certain to drain the air pressure from all reservoirs before beginning

ANY work on the vehicle. If the vehicle is equipped with an AD-IS air dryer system or a dryer reservoir module, be sure to drain the purge reservoir.

5. Following the vehicle manufacturer’s recommended procedures, deactivate the electrical system in a manner that safely removes all electrical power from the vehicle.

6. Never exceed manufacturer’s recommended pressures.

7. Never connect or disconnect a hose or line containing pressure; it may whip. Never remove a component or plug unless you are certain all system pressure has been depleted.

8. Use only genuine Bendix® replacement parts, components and kits. Replacement hardware, tubing, hose, fittings, etc. must be of equivalent size, type and strength as original equipment and be designed specifically for such applications and systems.

9. Components with stripped threads or damaged parts should be replaced rather than repaired. Do not attempt repairs requiring machining or welding unless specifically stated and approved by the vehicle and component manufacturer.

10. Prior to returning the vehicle to service, make certain all components and systems are restored to their proper operating condition.

FIGURE 8 - ELECTRICAL CONNECTOR

OPTIONAL

CONSTANT

POWER

(TRACTOR

IGNITION)

GROUND

OPTIONAL

TRACTOR

MOUNTED

STATUS

LIGHT

SENSOR 2

SNS 2

SENSOR 1

SNS 1

A B C D E F G

H J K L M N P

STOPLIGHT

SWITCH

POWER

OPTIONAL

TRAILER

MOUNTED

STATUS

LIGHT

SENSOR 2

SNS 2

SENSOR 1

SNS 1

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