Chevrolet Full Size Cars 1979-1989

Alternator

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OPERATION





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Fig. Fig. 1 "SI" series alternator



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Fig. Fig. 2 "CS" series alternator

Two types of alternators are used on these vehicles; the SI Delcotron series with 2 terminal integral regulator and the CS Delcotron series with the 4 terminal integral regulator. Most of the vehicles covered by this guide are equipped with the SI alternator, though a few 1988 and later vehicles may be equipped with the CS series. 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.

The alternator is belt-driven from the engine. Energy is supplied from the alternator/regulator system to the rotating field through two brushes to two slip-rings. The slip-rings are mounted on the rotor shaft and are connected to the field coil. This energy supplied to the rotating field from the battery is called excitation current and is used to initially energize the field to begin the generation of electricity. Once the alternator starts to generate electricity, the excitation current comes from its own output rather than the battery.

The alternator produces power in the form of alternating current. The alternating current is rectified by the rectifier diode bridge into direct current. The direct current is used to charge the battery and power the rest of the electrical systems on the vehicle.

When the ignition key is turned ON , current flows from the battery, through the charging system indicator light on the instrument panel, to the voltage regulator and the alternator. Since the alternator is not producing any current, the alternator warning light comes ON. When the engine is started, the alternator begins to produce current and turns the alternator light OFF. When the alternator is operating it recharges the battery and supplies power to the electrical systems of the vehicle. All charging systems require a control circuit to limit or regulate the alternator's output because as the alternator speed changes so will the output. Without a voltage regulator the alternator would overcharge the battery when engine rpm was high, while at low engine rpm an insufficient supply would cause the battery to become undercharged and some accessories would not operate at all. The voltage regulator monitors the battery's voltage and regulates the alternator's field current in order to control the alternator's output voltage. Most solid state voltage regulators also contain a temperature compensation circuit since ambient temperature will also affect battery charge.

The battery is connected to the alternator at all times, whether the ignition key is turned ON or not. If the battery were shorted to ground, the alternator would also be shorted. This would damage the alternator. To prevent this, a fusible link is installed in the wiring between the battery and the alternator. If the battery becomes shorted, the link will melt to protect the alternator.

ALTERNATOR PRECAUTIONS



Several precautions must be observed with alternator equipped vehicles to avoid damage to the unit.



If the battery is removed for any reason, make sure it is reconnected with the correct polarity. Reversing the battery connections may result in damage to the one-way rectifiers.
 
When utilizing a booster battery as a starting aid, always connect the positive to positive terminals and the negative terminal from the booster battery to a good engine ground on the vehicle being started.
 
Never use a fast charger as a booster to start vehicles.
 
Disconnect the battery cables when charging the battery with a fast charger; the charger has a tendency to force current through the diodes in the opposite direction for which they were designed.
 
Never attempt to polarize the alternator.
 
Do not use test lights of more than 12 volts when checking diode continuity.
 
Do not short across or ground any of the alternator terminals.
 
The polarity of the battery, alternator and regulator must be matched and considered before making any electrical connections within the system.
 
Never separate the alternator on an open circuit. Make sure all connections within the circuit are clean and tight.
 
Disconnect the battery ground terminal when performing any service on electrical components.
 
Disconnect the battery if arc welding is to be done on the vehicle.
 
Do not apply full battery voltage to the field (brown) connector.
 

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 of this guide.
  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


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Fig. Fig. 3 "SI" series alternator schematic

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.
  4.  
  5. If 10 volts or greater is measured go to the next step.
  6.  
  7. 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.
  8.  

  1. With the ignition ON , connect a voltmeter between the alternator's harness connector terminal 2 (red wire) and ground.
  2.  
  3. If 10 volts or greater is measured, go to the next step.
  4.  
  5. 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.  

  1. 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.
     

  2.  

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:

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

  10.  
  11. 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:

    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.
     

  12.  

Delcotron "CS" Alternators


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Fig. Fig. 4 "CS" series alternator schematic

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.  

  1. 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.
     

  2.  

  1. 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.
     

  2.  

REMOVAL





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Fig. Fig. 5 Alternator mounting through 1986 inline 6-cylinder engine (top), V6 and V8 engines (bottom)



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Fig. Fig. 6 1987 and later alternator mounting except police and taxi vehicles



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Fig. Fig. 7 Heavy duty alternator mounting police and taxi vehicles 1987 and later



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Fig. Fig. 8 Unplug the electrical connector from the side of the alternator



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Fig. Fig. 9 Pull back the rubber boot and remove the nut, then disconnect the ring terminal from the alternator



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Fig. Fig. 10 Remove the mounting and pivot bolts, as applicable



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Fig. Fig. 11 Remove the alternator from the vehicle

  1. Disconnect the negative battery cable to prevent diode damage and prevent the chance of shorting the battery cables.
  2.  
  3. Tag and disconnect the alternator wiring. Use a small screwdriver to release the locktab on the alternator connector, then use a wrench to loosen the stud nut and disconnect the terminal wiring.
  4.  

Most alternators which are installed on serpentine belt equipped engines are simply bolted into position. There are usually no adjusting or pivot bolts.

  1. Loosen the alternator lower though-bolt, then remove the alternator brace/adjuster bolt.
  2.  

If equipped with a serpentine drive belt, loosen the by using a breaker bar or ratchet to pivot the tensioner, then remove the belt from the necessary pulley(s).

  1. On some vehicles equipped with power steering, it may be necessary to loosen the pump brace and mount nuts, then detach the pump drive belt.
  2.  
  3. Pivot the alternator inward and remove the drive belt from the pulley.
  4.  
  5. Support the alternator and remove the lower mount bolt(s), then remove the unit from the vehicle.
  6.  

INSTALLATION AND BELT ADJUSTMENT



For more details on belt adjustment procedures, please refer to of this guide.

  1. Position the alternator in the vehicle and install, but do not fully tighten, the lower mounting and/or through-bolt(s).
  2.  
  3. Pivot the alternator inward and position the drive belt over the pulley.
  4.  

If equipped with a serpentine drive belt, hold the belt tensioner out of the way while you reposition the belt over the necessary pulley(s), then slowly allow the tension to tighten the belt. No further belt adjustment is necessary for these engines. Make sure the tensioner scale shows proper belt tension. Replace the belt if it is worn or loose.

  1. If removed earlier, install the power steering pump drive belt, adjust the tension and tighten the pump fasteners.
  2.  

Determine belt tension at a point halfway between the pulleys by pressing on the belt with moderate thumb pressure while the component is held or pried outward from the engine. The belt should deflect about 1 / 2 in. at the halfway point if the distance between the pulleys (measured from the center of each pulley) is 13-16 in. The belt should deflect 1 / 4 in. if the distance is 7-10 in. Once the proper deflection is achieved, the adjuster bolt should be tightened.

  1. Move the accessory toward or away from the engine until the tension is correct. You can use a wood hammer handle or broomstick as a lever, but do not use anything metallic.
  2.  
  3. Tighten the bolts and re-check the tension.
  4.  
  5. Install the alternator wiring as noted during removal. If equipped, make sure the rubber boot is properly positioned over the stud nut terminal at the rear of the alternator.
  6.  
  7. Connect the negative battery cable.
  8.  
  9. If new belts have been installed, run the engine for a few minutes, then re-check and readjust as necessary.
  10.  

If the driven component has two drive belts, the belts should be replaced in pairs to maintain proper tension. It is better to have belts too loose than too tight, because overtightened belts will lead to bearing failure, particularly in the water pump and alternator. However, loose belts may place an extremely high impact load on the driven components due to the whipping action of the belt.

 
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