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RESERVOIR
FIGURE 6 ANTILOCK MODE: SOLENOIDS ACTIVATED
2. With the service brakes released, coat the exhaust port
and the area around the retaining ring with a soap solution.
A 1" bubble in 3 seconds is permitted.
3. If leakage is excessive around the supply and exhaust
solenoids, replace the M-12
excessive leakage is detected where the solenoid
assembly and body meet, replace the M-12
modulator. If excessive leakage is detected at the exhaust
port, before replacing the M-12
perform the following test. Place the vehicle in park by
exhausting the air pressure from the emergency side of
the spring brake. Perform the leakage check.
ELECTRICAL TESTS
1. Before testing the solenoid assembly of a "suspect"
modulator, its location on the vehicle should be confirmed
using the Trouble Shooting or Start-Up procedure for the
specific antilock controller in use. (See the Service Data
Sheet for the antilock controller for this procedure.)
2. Proceed to the modulator in question and identify it as
an M-12
or M-12R
™
™
connector. In the case of an M-12
necessary to remove the four cap screws that secure
the controller to the modulator. The M-12R
has an external connector that can be tested without
removing the cover. Disconnect the connector and test
the resistance between the pins on the modulator. Refer
to figure 7.
EXHAUST
SOLENOID
SUPPLY
SOLENOID
SUPPLY
™
/M-12R
™
modulator. If
/M-12R
™
/M-12R
modulator,
™
™
modulator and inspect its wiring
modulator it will be
™
modulator
™
BRAKE
VALVE
CONTROL
DELIVERY
EXHAUST
For the FOUR pin connector test as follows
A.
Black to Black: Read 9 to 12 OHMS
B.
White to White: Read 9 to 12 OHMS
For the THREE pin connector on the M-12R test as
follows
A.
Red to Black:
™
B.
Red to White:
Note: If the resistance readings for the three pin connector
are NOT as shown, the wire harness leading to the to
the under side of the modulator cover may require repair
or replacement. Remove the cover (as discussed
elsewhere in this manual) and disconnect the four pin
connector and perform the tests shown for the FOUR
pin connector. If the resistance is correct at the four pin
connector the short wire harness between the four and
three pin connectors is at fault.
3. If the resistance values are NOT AS SHOWN, replace
the modulator.
WARNING! PLEASE READ AND FOLLOW
THESE
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.
DOUBLE
CHECK
CONTROL
PISTON
SERVICE BRAKE
CHAMBER
Read 9 to 12 OHMS
Read 9 to 12 OHMS
INSTRUCTIONS
TRAILER
TO
AVOID
5
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