TRUCK SERVICE MANUAL
ELECTRICAL
Connect voltmeter leads to ground on starting
Test No. 4No Load Test
motor and to ground post of battery. The allowable
After completing the cranking voltage test, battery
voltage drop of .2 volt is permissible. If more than .2 volt
capacity test and the voltage drop tests, and the starting
is obtained, a poor ground is present, such as a loose
motor still fails to function, remove the motor and make
starting motor mounting bolt, bad battery ground
the no load test as follows.
connector or ground connection to engine or frame,
depending upon the battery installation. The excessive
Note that the preceding tests were made in the
voltage drop is located in much the same manner as in
particular order to make certain the starting motor circuit
the preceding test working toward the battery.
is in good condition before needless starter motor
removal.
Control Circuit: High resistance in the control
circuit will reduce the current flow through the solenoid
windings, which can cause improper function of solenoid
Before performing the "No Load Test" look the
or not at all. Improper functioning of the solenoid could
motor over. The pinion should be checked to be sure it
result in burning of contacts in the solenoid causing high
is free by turning it on the screw shaft. The armature
resistance in the starting motor circuit.
should be checked so that it is free to rotate by prying the
pinion with a screw driver. Tight bearing, bent armature
To complete control circuit test, check the vehicle
shaft or loose pole shoe screws could cause the
circuit diagram to assist in locating the wires and
armature not to turn freely. The motor should be
particular switches involved in the chassis. Observe
disassembled if the armature does not turn freely.
polarity of voltmeter and connect leads to battery post
However, if the armature will rotate freely, the next step
and solenoid switch terminal as shown in Fig. 8. Crank
is to give the motor a no load test before disassembly.
engine using the vehicle ignition switch or push button if
equipped observing the voltmeter reading.
If the
Connect the starting motor in series with a fully
voltmeter shows less than .5 volt, the circuit is in good
charged battery of the specified voltage, an ammeter
condition. If more than .5 volt, this is an indication of
capable of reading several hundred amperes, and a
excessive resistance. However, with experience, slightly
variable resistance.
Also connect a voltmeter as
higher voltage loss will be found and will be normal.
illustrated in Fig. 9 from the motor terminal to the motor
frame. An R. P. M. indicator is necessary to measure
Isolate the point of high resistance by placing the
armature speed. Obtain the specified voltage by varying
voltmeter leads across each component in the circuit in
the resistance unit, then read the current draw and the
turn. A reading of more than . 1 volt across any one
armature speed and compare these readings with the
wire or switch is usually an indication of the trouble.
values listed in the specifications.
Fig. 9 No Load Test Hookup
DISASSE MB LY
Fig. 8 Control Circuit Test
If the starting motor does not perform according to
the specifications it will be necessary to disassemble it
for
further
tests
of
the
components.
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