Maintenance Instructions Page 39
CAUTION: Take precautions when
servicing brakes:
• Do not create or breathe dust.
• Do not machine, file, or grind the
brake linings.
• Do not use compressed air or dry
brushing for cleaning.
Lubrication
Before re-assembling the electric brakes, apply a light
film of anti-seize compound, or grease such as
“lubriplate,” on the:
• brake anchor pin
• actuating arm bushing and pin
• areas on the backing plate that are in contact with the
brake shoes and magnet lever arm
• actuating block on the actuating arm
I
MPORTANT: Do not allow grease to contact the brake
linings, drums, or magnets.
Magnets
The brakes’ electromagnets are designed to provide the
proper input force and friction.
Inspect the magnets regularly, and replace if they become
unevenly worn. Use a tool with a straight edge to check
wear.
Even if the wear is normal, you should replace the
magnets if any part of the magnet coil is visible through
the friction material on the magnet face. Replace the
magnets in pairs (both sides of an axle).
When replacing the magnets, also resurface the drum
armature surface.
How to Measure Brake Voltage
1. Keep the engine of the tow vehicle running so that a
low battery will not affect the voltage readings.
2. Measure the voltage at the magnets by connecting a
voltmeter to the two magnet lead wires at any brake.
3. Insert a pin probe through the insulation of the
magnet lead wires dropping down from the chassis.
The voltage should be modulated, beginning at 0 V and
gradually increasing to about 12 V as the controller bar is
slowly actuated. Modulation is absent when the controller
provides an immediate high voltage to the brakes, which
fully energizes them.
The voltage that is applied to the brakes when the
controller first turns on is called the threshold voltage.
The lower the threshold voltage, the smoother the brakes
will operate. A threshold voltage over 2 V can cause
harsh, jerky brakes.
How to Measure Brake Amperage
The brake system amperage is the total current that is
drawn by all brakes on the MH-400. To measure the total
amperage:
1. Keep the engine of the tow vehicle running.
2. Disconnect the blue wire running between the load
control and the brakes and place an ammeter in series
into the line.
Note – To prevent damage to the ammeter, ensure that
the ammeter has sufficient capacity. Note the polarity.
3. Measure amperage at the blue wire of the controller,
which is the output to the brakes.
The total amperage draw should be 12 A (3 A per magnet).
To measure the individual amperage at one magnet:
1. Insert the ammeter in the line at the magnet you want
to check.
2. Disconnect one of the magnet lead wire connectors.
3. Attach the ammeter between the two wires.
Reconnect and seal all wires after testing.
How to Track the Conveyor Belt
If the conveyor belt is not centered and tracks to one side,
it needs to be adjusted (Figure 27). The best time to do
this is between loads during operation.
1. Go to the rear of the MH-400 and determine which
side the belt is touching.
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