6
PREVENTIVE MAINTENANCE
GENERAL
Perform the tests and inspections presented at the
prescribed intervals. If the modulator fails to function as
described, or leakage is excessive, it should be replaced
with a new Bendix unit, available at any authorized parts
outlet.
EVERY MONTH, 10,000 MILES OR 350
OPERATING HOURS
1. Remove any accumulated contaminates and visually
inspecttheexteriorfor excessivecorrosionandphysical
damage.
2. Inspect all air lines and wire harnesses connected to
the modulator for signs of wear or physical damage.
Replaceas necessary.
3. Testairlinefittingsfor leakage and tighten orreplaceas
necessary.
4. Perform the ROUTINE OPERATION AND LEAKAGE
TESTINGdescribedinthismanual.
OPERATION & LEAKAGE TESTS
LEAKAGE TEST
1. Park the vehicle on a level surface and block or chock
the wheels. Release the parking brakes and build the
air system to full pressure.
2. TurntheengineOFFandmake4or5brakeapplications
and note that the service brakes apply and release
promptly.
3. Build system pressure to governor cut-out and turn the
engineOFF.
4. After determining the pressure loss with the brakes
released (2 PSI/minute allowed), make and hold a full
servicebrakeapplication. Allow thepressuretostabilize
foroneminute.
5. Begintimingpressurelossfor twominuteswhilewatch-
ingthe dash gauges for apressure drop. The leakage
ratefortheservicereservoirsshouldnotexceed3 PSI/
minute.
6. If either circuit exceeds the recommended two PSI/
minute, apply soap solution to the exhaust port of the
modulatorandanyothercomponentsintherespective
circuit.
7. Theleakageatthe exhaust portofmostBendixcompo-
nents,includingM-32™modulators,shouldnotexceed
a one-inch bubble in three seconds. If leakage at the
modulator is determined to exceed the maximum
limits, replace the modulator.
OPERATION TEST
Toproperlytestthefunctionof themodulatorwillrequiretwo
(2)servicetechnicians.
1. Park the vehicle on a level surface and block or chock
the wheels. Release the parking brakes and build the
air system to governor cut out.
2. Turn the engine ignition key to the OFF position then
makeand hold a full brake application.
3. With the brake application held and one (1) service
technicianpostedatone (1) of the modulators, turn the
vehicle ignition key to the ON position. ONE OR TWO
SHORT bursts of air pressure should be noted at the
modulatorexhaust.Repeatthetest for each modulator
onthevehicle.Ifatleasta single burst of exhaust is not
noted or the exhaust of air is prolonged and not short,
sharpandwell defined, perform the ElectricalTests.
ELECTRICALTESTS
1. Before testing the solenoid assembly of a suspect
modulator,itslocationonthevehicleshouldbeconfirmed
usingtheTroubleShooting orStartUp procedureforthe
specificantilockcontrollerinuse. (See theServiceData
Sheetfortheantilockcontroller for this procedure.)
2. Proceed to the modulator in question and inspect its
wiringconnector.Disconnect the connectorandtestthe
resistance between the pins ON THE MODULATOR.
RefertoFigures10and11.
A. HOLDTOSOURCE(41-42):Read4.9to5.5Ohms.
B. EXHAUSTTOSOURCE(43-41):Read4.9to5.5Ohms.
C. EXHAUSTTO HOLD(43-42):Read9.8to11.0 Ohms.
D. Individually test the resistance of each pin to vehicle
groundandnotethere isNOCONTINUITY.
Iftheresistancereadingsareasshown,thewireharness
leading to the modulator may require repair or
replacement. Before attempting repair or replacement
ofthewireharness,refertothetestprocedures specified
fortheantilockcontrollerinuseforpossiblefurthertesting
that may be required to substantiate the wire harness
problem.IftheresistancevaluesareNOTASSTATED,
replacethemodulator.
WARNING! PLEASE READ AND FOLLOW
THESE INSTRUCTIONS TO AVOID
PERSONAL INJURYOR 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.
