GM Full-Size Trucks 1980-1987 Repair Guide

Alternator

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See Figures 1 and 2

Two types of alternators are used on General Motors trucks; the SI Delcotron series with 2 terminal integral regulator and the CS-130 Delcotron series with the 4 terminal integral regulator. The alternator charging system is a negative (-) ground system which consists of an alternator, a regulator, a charge indicator, a storage battery and wiring connecting the components, and fuse link wire.



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Fig. Fig. 1: "SI" series alternator



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Fig. Fig. 2: "CS" series alternator

ALTERNATOR PRECAUTIONS



To prevent damage to the alternator and regulator, the following precautionary measures must be taken when working with the electrical system.

  1. Never reverse the battery connections. Always check the battery polarity visually. This is to be done before any connections are made to ensure that all of the connections correspond to the battery ground polarity of the car.
  2.  
  3. Booster batteries must be connected properly. Make sure the positive cable of the booster battery is connected to the positive terminal of the battery which is getting the boost.
  4.  
  5. Disconnect the battery cables before using a fast charger; the charger has a tendency to force current through the diodes in the opposite direction for which they were designed.
  6.  
  7. Never use a fast charger as a booster for starting the car.
  8.  
  9. Never disconnect the voltage regulator while the engine is running, unless instructed in the testing procedures.
  10.  
  11. Do not ground the alternator output terminal.
  12.  
  13. Do not operate the alternator on an open circuit with the field energized.
  14.  
  15. Do not attempt to polarize the alternator.
  16.  
  17. Disconnect the battery cables and remove the alternator before using an electric arc welder on the car.
  18.  
  19. Protect the alternator from excessive moisture. If the engine is to be steam cleaned, cover or remove the alternator.
  20.  

TESTING



Preliminary Charging System Tests
  1. If you suspect a defect in your charging system, first perform these general checks before going on to more specific tests.
  2.  
  3. Check the condition of the alternator belt and tighten it if necessary.
  4.  
  5. Clean the battery cable connections at the battery. Make sure the connections between the battery wires and the battery clamps are good.
  6.  
  7. Test the battery cables as outlined in Routine Maintenance .
  8.  
  9. Check the charging system wiring for any obvious breaks or shorts.
  10.  
  11. Check the battery to make sure it is fully charged and in good condition.
  12.  
  13. If all the previous checks were OK, proceed to the applicable test.
  14.  

Delcotron "SI" Series Alternator

See Figure 3

Delcotron "SI" alternators can be identified by having a two terminal integral voltage regulator connector. Delcotron "CS" alternators are identified by having a four terminal integral voltage regulator connector on the alternator.

CHARGING SYSTEM STATIC TEST
  1. Disconnect the two terminal connector at the alternator.
  2.  
  3. With the ignition on, connect a voltmeter between the alternator's harness connector terminal 1(brown wire) and ground.

    If 10 volts or greater is measured go to the next step.
     
    If no voltage is measured, repair the short to ground in the wiring between the generator light in the instrument panel and the alternator connector.
     

  4.  
  5. With the ignition on, connect a voltmeter between the alternator's harness connector terminal 2 (red wire) and ground.

    If 10 volts or greater is measured, go to the next step.
     
    If no voltage is measured, repair the open or short to ground in the wire between the alternator and the fusible link at the starter solenoid.
     

  6.  
  7. Measure voltage at the alternator between the "BAT" ring terminal and ground.

    If 10 volts or greater is measured, perform the alternator output test.
     
    If no voltage is measured, repair the open in the wiring.
     

  8.  



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Fig. Fig. 3: "SI" series alternator schematic

ALTERNATOR OUTPUT TEST

This test can only be performed on Delcotron "SI" type alternators which have the alternator field ground tab test hole. This test cannot be performed on the Delcotron "CS" type alternators. An ammeter is required to perform this test.

Delcotron "SI" alternators can be identified by having a two terminal integral voltage regulator connector. Delcotron "CS" alternators are identified by having a four terminal integral voltage regulator connector on the alternator.

  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the battery terminal on the alternator.
  4.  
  5. Connect the ammeter's negative lead to the battery wire disconnected in the previous step.
  6.  
  7. Reconnect the negative battery cable and turn on all lights and accessories. Leave the lights and accessories on for a minute or two to draw down the battery a little before going on to the next step.
  8.  
  9. Start the engine and run it until you obtain a maximum current reading on the ammeter. Make sure all accessories are on blower motor, wipers, air conditioning, high beam headlights, etc. Record the reading and compare to the alternator's rated output, which is stamped onto the frame of the alternator. If the reading is:
  10.  



Within 10 percent of the rated output, the alternator is good.
 
Not within 10 percent of the rated output go to the next step.
 

  1. With the engine running at moderate speed and all accessories on, ground the alternator field. This can be done by inserting a insulated screwdriver in the alternator field test hole and allowing the screwdriver shaft to touch the alternator case. Again record the reading and compare to the alternator's rated output, which is stamped onto the frame of the alternator. If the reading is:
  2.  



Within 10 percent of the rated output, the alternator's regulator is most likely defective.
 
Not within 10 percent of the rated output, the problem is with either the alternator's field winding, diode trio, rectifier bridge or stator.
 

Delcotron "CS" Generators

Delcotron "SI" alternators can be identified by having a two terminal integral voltage regulator connector. Delcotron "CS" alternators are identified by having a four terminal integral voltage regulator connector on the alternator.

  1. Disconnect the four terminal connector at the alternator.
  2.  
  3. With the ignition on, connect a voltmeter between the alternator's harness connector terminal "L" (brown wire) and ground.

    If 10 volts or greater is measured go to the next step.
     
    If no voltage is measured, repair the short to ground in the wiring between the generator light in the instrument panel and the alternator connector.
     

  4.  
  5. With the ignition on, connect a voltmeter between the alternator's harness connector terminal "I" (red or pink wire) and ground.

    If 10 volts or greater is measured, go to the next step.
     
    If no voltage is measured, repair the open or short to ground in the wire between the alternator and the fusible link at the starter solenoid.
     

  6.  
  7. Measure voltage at the alternator between the "BAT" ring terminal and ground.

    If 10 volts or greater is measured, the problem is in the alternator. Remove the alternator for repair or replacement.
     
    If no voltage is measured, repair the open in the wiring.
     

  8.  



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Fig. Fig. 4: "CS" series alternator schematic

REMOVAL & INSTALLATION



See Figures 5, 6, 7, 8, 9, 10, 11, 12, 13 and 14

  1. Disconnect negative battery cable, then disconnect the positive cable from the battery.
  2.  
  3. Disconnect and tag all wiring to the alternator.
  4.  



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Fig. Fig. 5: Some of the alternator wiring is at a ring terminal located under a protective rubber boot on the rear of the alternator



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Fig. Fig. 6: A small box or open-end wrench may be used to loosen the wiring retaining nut



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Fig. Fig. 7: Squeeze the locktab and disengage the connector from the side of the alternator housing

  1. If necessary for removal clearance, disconnect the ground strap from the alternator bracket.
  2.  
  3. If equipped, remove the alternator brace bolt.
  4.  
  5. If the truck is equipped with power steering, it may be necessary to loosen the pump brace and mount nuts.
  6.  
  7. Remove the lower mounting bolt, then support the alternator and remove the upper mounting/adjusting bolt.
  8.  
  9. Slip the alternator belt from the pulley and remove the alternator from the truck.
  10.  



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Fig. Fig. 8: Loosen the lower mounting bolt



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Fig. Fig. 9: The alternator uses a very long lower mounting bolt which passes through the alternator housing and a bushing before threading into the engine block



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Fig. Fig. 10: Support the alternator by hand and unthread the upper mounting/adjustment bolt

  1. Installation is the reverse of removal. Be sure that the bushing is in place when the lower mounting bolt is installed. Should the bolt be torqued without the bushing in position, alternator housing damage would likely occur.
  2.  
  3. Adjust the belt(s) to have 1 /4- 1 /2 inch depression under thumb pressure on its longest run.
  4.  



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Fig. Fig. 11: Once the alternator is free, it may be lowered slightly so the belt may be removed from its pulley



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Fig. Fig. 12: Remove the alternator housing from the vehicle by lifting upward



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Fig. Fig. 13: During installation, carefully pry outward on the alternator in order to adjust the belt tension



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Fig. Fig. 14: Alternator mounting, in-line 6 and gasoline V8 engines

 
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