4-24. ELECTRICAL SYSTEM - Continued
Press cab START button, with ignition ON. Be sure main engine cranks at good speed and when button is
released, starter motor disengages. A distinct pull-in of the solenoid will be heard just prior to the motor
Starting motor must be removed from truck prior to repair. When repairing, only disassemble motor so far as is
necessary to make repair or replace defective parts.
Check armature rotates freely by prying pinion with a screwdriver. If the armature does not turn freely,
disassemble starter to find cause (see step 9 following). Otherwise proceed with tests 2-8.
Connect starter motor to test gear as shown. Be sure battery is fully charged.
Close switch and note the reading on the voltmeter, ammeter and rpm indicator. At a voltage of between
10 and 13 volts, a healthy motor will have a current draw of between 140 - 215A at a speed of 4000 - 7000
Low speed and high current indicates.
tight, dirty, or worn bearings
loose pole shoes
bent armature shaft
grounded armature or field
No speed and high current indicates:
direct ground in terminal or fields
No speed and no current draw indicates:
open field circuit
open armature coils
broken brush springs, worn brushes, high insulation between commutator bars or other causes
preventing good contact between brushes and commutator