GMC T Series 1994 Repair Manual page 591

46. CARBON PILE
47. BATTERY
48. AMMETER
N O T I C E : N e v e r o p e r a t e
m o r e t h a n 3 0 s e c o n d s a t a
p a u s i n g to a l l o w i t to c o o l f o r a t le a s t 2 m in ­
u t e s . O v e r h e a t i n g , c a u s e d
c r a n k in g , w ill d a m a g e th e s t a r t e r m o to r .
1. Momentarily close the switch.
• If there is high current flow and the starter
motor fails to operate, release the switch imme­
diately. Internal mechanical damage is indicat­
ed.
• If there is no current flow and the starter motor
fails to operate, release the switch immediately.
An open circuit is indicated.
• If there is current flow and the starter motor
operates, release the switch and proceed with
the next step.
2. Close the switch and compare the RPM, ammeter,
and voltmeter readings with the specifications at
the end of this section. It is not necessary to obtain
the exact voltage specified as a good reading can
be made by understanding that if the voltage is
slightly higher the RPM will be slightly higher, with
the current remaining basically unchanged. Howev­
er, if the exact voltage is desired, a carbon pile
connected across the battery can be used to
reduce the voltage to the specified value as
described in step 3.
3. Close the switch and observe the voltmeter. Adjust
the carbon pile load until the voltmeter reads 10
volts. Record the ammeter and RPM readings.
Open the switch.
Figure 2— No-Load Test Connections
t h e s t a r t e r m o t o r
t i m e w i t h o u t
b y t o o m u c h
48
4. Compare the ammeter and RPM readings to those
listed under " Specifications." If the readings are
outside the limits shown, refer to the list below. If
the readings are within the limits, the starter motor
is operating normally.
Troubleshooting
1. Rated current draw and no-load speed indicates
normal condition of the starter motor.
2. Current flow with the test switch open indicates the
solenoid switch contacts are stuck closed.
3. Low free speed and high current draw indicates:
• Too much friction. Tight, dirty, or worn bear­
ings, bent armature shaft, or loose pole shoes
allowing the armature to drag.
• Shorted armature. This can be further checked
on a growler after disassembly.
• Grounded armature or fields. Check further
after disassembly.
4. Failure to operate with high current draw indicates:
• A direct ground in the terminal or fields.
• Seized bearings. This should have been noted
by turning the armature by hand.
5. Failure to operate with no current draw indicates:
• Open field circuit. This can be checked after
disassembly by inspecting internal connections
and tracing the circuit with a test lamp.
• Open armature coils. Inspect the commutator
for badly burned bars after disassembly.
• Broken brush springs, worn brushes. High
insulation between the commutator bars or oth­
er causes that would prevent good contact
between the brushes and commutator.
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V3861