Airstream INTERNATIONAL TRAILER, Owner'S Manual

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AIRSTREAM INTERNATIONAL TRAILER OWNERS MANUAL
D-17
SHOES AND LININGS
A simple visual inspection of your brake linings will tell if they are usable. Replacement is necessary if the
lining is worn thin (1/16" or less), contaminated with grease or oil, or abnormally scored or gouged. It is
important to replace both shoes on each brake and both brakes of the same axle. This is necessary to retain
the "balance" of your brakes.
TROUBLE SHOOTING
Most brake malfunctions that cannot be corrected by either brake adjustment or synchronization
adjustments can generally be traced to electrical system failures. Mechanical causes are ordinarily obvious,
i.e. bent or broken parts, worn out linings or magnets, seized lever arms or shoes, scored drums, loose parts,
etc. Electrically, a voltmeter and ammeter are essential for proper troubleshooting
HOW TO MEASURE VOLTAGE
System voltage is measured at the magnets by connecting the voltmeter to the two magnet lead wires at any
brake. This may be accomplished by using a pin probe inserted through the insulation of the wires dropping
down from the chassis or by cutting the wires. The engine of the towing vehicle should be running when
checking the voltage so that low batteries will not affect the readings.
Voltage in the system should begin at 0 volts and as the controller bar is slowly actuated, should gradually
increase to about 12 volts. This is referred to as modulation. No modulation means that when the controller
begins to apply voltage to the brakes it applies an immediate high voltage, which causes the brakes to apply
instantaneous maximum power.
The threshold voltage of a controller is
the voltage applied to the brakes when
the controller first turns on. The lower
the threshold voltage the smoother the
brakes will operate. Too high of a
threshold voltage (in excess of 2 volts as
quite often found in heavy duty
controllers) can cause grabby harsh
brakes.
HOW TO MEASURE AMPERAGE
System amperage is the amperage being
drawn by all brakes on the trailer. The
engine of the towing vehicle should be
running when checking amperage. One
place to measure system amperage is at the BLUE wire of the controller, which is the output to the brakes.
The BLUE wire must be disconnected and the ammeter put into the line. System amperage draw should be
as noted in the table following. Make sure your ammeter has sufficient capacity and note polarity to prevent
damaging your ammeter. If a resistor is used in the brake system it must be set at zero or by-passed
completely to obtain the maximum amperage reading.