GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC C-Series Medium Duty Truck B7 🢒 Engine 🢒 Engine Electrical 🢒 Starter No Load Test

Object Number: 103972 Size: SH
  1. Connect a voltmeter from the motor terminal to the motor frame.

    2. On starter motors with ground terminals, connect the voltmeter to the ground terminals rather than the frame.

  2. Use an RPM indicator in order to measure pinion speed.
  3. Connect the motor and an ammeter in series with the following components:
    4. • A fully charged battery of the specified voltage
    • A switch in the open position from the solenoid battery terminal to the solenoid switch terminal.
  4. Close the switch.
  5. Compare the following measurements with the no load test specified values for the 28-MT and 37-MT Starter Motors in Starter Motor Usage :
    6. • RPM
    • Current
    • Voltage
  6. Evaluate the measurements by understanding that it is not necessary to obtain the exact voltage specified. A good reading can be made by understanding that if the voltage is slightly higher, the RPM will be slightly higher and the current will remain basically unchanged
  7. Use the following procedure in order to obtain the exact specified voltage (if desired):
    8. 7.1. Connect a carbon pile across the battery.
    7.2. Compare the reduced voltage with the no load test specified values for the 28-MT and 37-MT Starter Motors in Starter Motor Usage :
  8. Disconnect the circuit only with the switch open.
  9. Use the following information in order to interpret the test results:
    10. 9.1. Rated current draw and no-load speed indicate normal condition of the starter motor.
    9.2. Low free speed and high current draw indicate the following conditions:
       • Excessive friction
       • Tight, dirty, or worn bearings, a bent armature shaft or loose pole shoes allow the armature to drag.
       • A shorted armature
       • Inspect a shorted armature on a growler after disassembly.
       • Grounded armature fields
       • Verify the grounded armature after disassembly.
    9.3. Failure to operate with no current draw indicates the following conditions:
       • A direct ground
       • A direct ground exists in the terminal or fields.
       • Seized bearings
       • Seized bearings should have been noted by hand turning the armature by hand.
    9.4. Failure to operate with no current draw indicates the following conditions:
       • An open field circuit
       • An open field circuit can be checked after disassembly by inspecting the internal connections and tracing the circuit with a self-powered test lamp.
       • Open armature coils
       • Inspect the commutator for badly burned bars.
       • Broken brush springs, worn brushes
       • High insulation between the commutator bars or other causes which would prevent proper contact between the brushes and the commutator.
    9.5. Low no-load speed and low current draw indicate a higher internal resistance due to the following conditions:
       • Poor connections
       • Defective leads
       • A dirty commutator
       • An open field circuit
       • Open armature coils
       • Broken brush springs, worn brushes
    9.6. High free speed and high current draw indicate shorted fields. If shorted fields are suspected, replace the field coil assembly and inspect for improved performance.