See Figures 1, 2 and 3
The alternating current generator (alternator) supplies a continuous amount of electrical energy at all engine speeds to keep the battery fully charged. The Corvette, as all other GM vehicles, uses a Delcotron alternator. Delcotron is a trade name of the Delco designed alternator.
The alternator consists of four main assemblies: drive (pulley) end frame, slip ring (rear) end frame, stator, and rotor. The drive end frame houses a ball bearing which is used to support the front of the rotor and is large enough to withstand the side loads imposed on the rotor by the alternator belt. The slip ring end frame uses a small roller bearing which is used to support the rear of the rotor (The "perforated case" Delcotron uses a ball bearing in the rear, also). These bearings are lubricated during their assembly and need no additional lubrication. If you replace the bearings, try to obtain a fully sealed bearing for the front, to further increase bearing life.
The stator has a laminated core which is attached to the frame of the alternator. On "perforated case" models, the stator is serviced with the main case. A large number of windings cover the inside diameter of the stator, and it is within this circle that the rotor turns. Current passes from two brushes through the slip rings (of the rotor) and finally to the field coils which are wound in a manner concentric to the rotor shaft.
Both the internally and externally regulated Delcotrons use positive and negative diodes. These diodes are electrical check valves, meaning that they will allow current to pass freely in only one direction. The diodes perform the function of changing the alternating current (AC) developed within the stator windings to direct current (DC) which can be used by the 12VDC system. In the externally regulated Delcotron (except the "perforated case" models), the negative diodes (3) are pressed into the slip ring end frame; the positive diodes (3) are pressed into an electrically insulated heat sink attached to the slip ring end frame. The diodes used in the "perforated case" Delcotron are pressed into removable heat sinks. The grounded heat sink contains the negative diodes; the insulated contains the positive. Internally regulated Delcotrons use a different type of diode arrangement. In these models, the negative diodes are permanently mounted in a rectifier bridge assembly. The rectifier bridge utilizes a finned aluminum heat sink for efficient diode cooling, and is mounted inside the slip ring end frame. A positive diode trio is used instead of separately mounted positive diodes. If a negative diode of the rectifier bridge fails, the rectifier bridge assembly must be replaced. Also, the positive diode trio can only be replaced as a unit.
Generally, internally and externally regulated alternators can easily be distinguished by the type of plug-in connector which is used at the alternator. External regulator models use a connector having two side-by-side vertical spade terminals, whereas the internal regulator type uses a connector having two side-by-side horizontal spade terminals. All "perforated case" Delcotrons use external voltage regulators.
Adjustments can be made to the external type of regulator (covered later in this section). The internally mounted voltage regulator is non-adjustable-if it is defective, it must be replaced.
To prevent damage to the alternator and regulator, the following precautions should be taken when working with the electrical system.
- Never reverse the battery connections.
- Booster batteries for starting must be connected properly-positive-to-positive and negative-to-negative.
- 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. This burns out the diodes.
- Never use a fast charger as a booster for starting the vehicle.
- Never disconnect the voltage regulator while the engine is running.
- Avoid long soldering times when replacing diodes or transistors. Prolonged heat is damaging to AC generators.
- Do not use test lamps of more than 12 volts (V) for checking diode continuity.
- Do not short across or ground any of the terminals on the AC generator.
- The polarity of the battery, generator, and regulator must be matched and considered before making any electrical connections within the system.
- Never operate the alternator on an open circuit. Make sure that all connections within the circuit are clean and tight.
- Disconnect the battery terminals when performing any service on the electrical system. This will eliminate the possibility of accidental reversal of polarity.
- Disconnect the battery ground cable if arc welding is to be done on any part of the car.
EXTERNALLY REGULATED ON-CAR CHARGING SYSTEM TESTS
These are quick checks that will allow the tester to isolate the general source of charging circuit difficulty in either the alternator, regulator, or wiring harness. Once the defective component has been singled out, further checks and repairs may be made using the procedures given in the alternator or regulator sections. Make these checks after looking for obvious problems such as a weak battery or loose fan belt.
Start the engine and bring the idle to between 1,500-2,000 rpm. Turn off all accessories, lights, radio, etc., and then disconnect the battery ground cable. If the engine stops, it is safe to assume that the alternator is at fault. If, however, the engine continues to operate, the problem lies with either the regulator or wiring harness.
Having eliminated the alternator from suspicion, the next step is to isolate the regulator from the harness and the easiest way is to substitute a known component. Remove the push-on wiring connector from the regulator and insert a regulator that is known to be good into the circuit, remembering to ground the regulator to the car. Idle the engine, remove the battery cable, and check the ammeter. If it indicates a discharge condition, then the possible problem is an open resistor or a shorted, positive diode. If the ammeter continues to indicate a charge, then it is the regulator that is defective.
Prepare the alternator for testing by disconnecting the battery ground terminal, the BAT, light relay, field, and GRD leads from the alternator terminals.
Check the positive diodes by connecting an ohmmeter between the R (or light relay) and BAT terminals, and noting the lowest range on the ohmmeter scale. It should indicate very low resistance. Reversing the connections should result in an infinitely high resistance indication.
If the ohmmeter reads low or high in both directions, the diodes, are defective. A low reading could also indicate a grounded stator.
To test for an open field, connect the ohmmeter between the F (or Field) and GRD terminals and check the low range scale for a reading between 7 and 20 ohms. A zero indication or one of excessively high resistance suggests a faulty alternator.
Field Relay Tests
Fasten one voltmeter lead to the no. two regulator terminal and ground the other lead to the regulator. Idle the engine between 1,500 and 2,000 rpm. If the GEN light still burns, and a volt reading of 3.5 to 6.5 is present, then the regulator field relay is faulty.
Accessory Circuit Resistance Tests
A resistor is connected to the ACC terminal ignition switch. To check for an open resistor, connect the voltmeter to the no. 4 connection of the regulator and ground the other voltmeter lead to the regulator. A zero reading, with the ignition switch turned to the ACC notch, indicates an open resistor. The resistance wire is an integral part of the ignition harness and carries a rating minimum of 10 ohms, 6.25 watts. The wire is not solderable and must be crimp-connected.
INTERNALLY REGULATED SYSTEM TESTING
Alternator Output Test
See Figure 4
- Connect a test voltmeter, ammeter, and a 10-ohm, 6-watt resistor into the charging circuit. Do not connect the carbon pile to the battery posts at this time.
- Increase alternator speed and observe the voltmeter-if the voltage is uncontrolled with speed and increases to 16 volts or more, check for a grounded brush lead clip as previously covered. If a brush lead clip is not grounded, the voltage regulator is faulty and must be replaced.
- Connect the carbon pile load to the battery terminals.
- Operate the alternator at moderate speed and adjust the carbon pile to obtain maximum alternator output as indicated on the ammeter. If output is within 10% of rated output as stamped on the alternator frame, alternator is O.K. If output is not within specifications, ground the alternator field by inserting a screwdriver into the test hole in the end frame. If output now is within 10% of rating, replace the voltage regulator; if still not within specifications, check field winding, diode trio, rectifier bridge and stator, as described later.
Low Charging Rate Diagnosis
- After battery condition, drive belt tension, and wiring terminals and connections have been checked, charge the battery fully and perform the following test:
- Connect a test voltmeter between the alternator BAT, terminal and ground, ignition switch ON. Connect the voltmeter in turn to alternator terminals No. 1 and No. 2, the other voltmeter lead being grounded as before. A zero reading indicates an open circuit between the battery and each connection at the alternator. If this test discloses no faults in the wiring, proceed to Step 3.
- Connect the test voltmeter to the alternator BAT terminal (the other test lead to ground), start the engine and run at 1,500-2,000 rpm with all lights and electrical accessories turned on. If the voltmeter reads 12.8 volts or greater, the alternator is good and no further checks need be made. If the voltmeter reads less than 12.8 volts, ground the field winding by inserting a screwdriver into the test hole in the end frame.
- If voltage increases to 13 volts or more, the regulator unit is defective;
- If voltage does not increase significantly, the generator is defective.
High Charging Rate Diagnosis
- With the battery fully charged, connect a voltmeter between alternator terminal No. 2 and ground. If the reading is zero, No. 2 circuit from the battery is open.
If No. 2 circuit is OK, but an obvious overcharging condition still exists, proceed as follows:
- Remove the alternator and separate the end frames;
- Connect a low-range ohmmeter between the brush lead clip and the end frame (Test 1), then reverse the connections. If both readings are zero, either the brush lead clip is grounded or the regulator is defective. A grounded brush lead clip can be due to damaged insulating sleeve or omission of the insulating washer.
REMOVAL & INSTALLATION
See Figures 5, 6, 7 and 8
- Disconnect the negative battery cable at the battery; this will prevent damaging the alternator diodes.
- Disconnect the wiring from the rear of the alternator (bolt-on and push-in connectors).
- Loosen the lower alternator bolt and remove the upper (adjustment) bolt. Slip the drive belt off of the pulley.
- Remove the pivot bolt and lift the alternator out of its mounting brackets.
- Installation of the alternator is the reverse of the previous steps. Adjust the drive belt to the proper tension.
DISASSEMBLY & ASSEMBLY
EXCEPT PERFORATED CASE MODELS
Externally Regulated Type
Remove the pulley by positioning a box-end wrench over the pulley retaining nut and inserting a 5 / 16 in. allen wrench in the shaft to prevent it from turning. Unbolt the retaining nut and slide it off the pulley. Disconnect the battery ground strap to prevent diode damage and remove the generator. On the 6.2 in. perforated case generator, remove the blade-connector retaining nuts and remove the connectors. Slip the indicator light relay from the terminal post, then back out the retaining screws, and remove the brush holder. Leave the capacitor attached to the generator. Remove the four, long, case bolts and separate the end frame and rotor assembly from the stator assembly. Cover the slip ring and bearing with tape to prevent contamination.
Remove the rotor from the end frame. Extract the retainer plate screws and remove the retainer plate and the end frame bearing. Remove the three attaching screws and separate the stator from the end frame. Remove the heat sink.
Wash all metal parts with the exception of the stator and rotor assemblies. The rotor slip rings may be cleaned with 400 grain polishing cloth. It is a good idea to rotate the rotor while doing this to guard against rubbing flat spots on the slip rings. Maximum out-of-round tolerance for slip rings is 0.001 in. Remove as little metal as possible when truing on a lathe. Polish with 400 grain cloth and blow dry.
To assemble the alternator:
Attach the slip-ring end frame to the stator assembly and position the diode connectors above the diode, relay, and stator leads. Tighten the terminal nuts, then slide the front end frame over the rotor. Slide on the spacer, pulley, washer, and nut, and torque the shaft to 50-60 ft. lbs. Attach the slip-ring end frame and stator to the rotor and drive end frame assembly and insert and tighten the thru-bolts.PERFORATED CASE MODELS
- Mount the alternator in a vise, clamping the drive end mounting flange lengthwise.
- Remove the two screws which secure the cover to the brush holder and remove the cover.
- Remove the nut which retains the indicator light wire to the blade connector post. Disconnect the wire from the connector post.
- Remove the two brush holder assembly attaching screws and remove the brush holder.
The capacitor lead is connected inside the alternator; the capacitor must stay with the alternator to avoid overstressing the lead wire.
- Scribe alignment marks to indicate the relationships between the end frames and the main base. These components must be properly aligned during assembly.
- Remove the slip ring (rear) end frame attaching bolts (3) and carefully pry the end frame off of the main case assembly. Pry around the circumference of the frame to avoid damaging the frame.
- Remove the drive end frame attaching bolts (3).
- Remove the end frame, rotor, and pulley as an assembly.
- Remove the shaft nut, washer, pulley, and woodruff key from the rotor shaft and slide the rotor out of the end frame.
If you plan to test the diodes and stator, disconnect the stator leads from the diodes using either of the following methods:
- Cut the leads between the stator windings and the diodes.
- Scrape the epoxy coatings from the leads and unsolder the leads from the diodes.
- Remove the heat sink retaining screws and remove the heat sinks. Remember that the insulated heat sink contains the positive diodes and that the insulated heat sink is the one with the "batt" terminal.
- Testing and/or replacement of bearings or diodes should be performed at this time, if necessary.
Assembly of the alternator is the reverse of the previous steps. Note the following points during assembly:
- Refer to the illustration which accompanies the "Brush and Holder Replacement" procedure for wiring information.
- Solder the stator lead-to-diode connections, if separated during step 10.
- Align the scribed marks made during disassembly.
- Lightly clamp the pulley in a soft-jawed vise when installing the pulley nut. Torque the pulley nut to 50-60 ft. lbs.
- When installing the brush holder, push each brush into the holder and retain with a straightened paper clip during installation. Remove the clip after the holder is installed.
Internally Regulated Type
- Place alternator in a vise, clamped by the mounting flange only.
- Remove the four through bolts and separate the slip ring end frame and stator assembly from the drive end and rotor assembly, using a screwdriver to pry the two sections apart. Use the slots provided for the purpose.
Scribe matchmarks on the parts to aid in assembly.
- Place a piece of tape over the slip ring end frame bearing to prevent entry of dirt; also tape shaft at slip ring end to prevent scratches.
- Clean brushes, if they are to be reused, with trichloroethylene or carbon tetrachloride solvent. Use these solvents only in an adequately ventilated area.
- Remove the stator lead nuts and separate the stator from the end frame.
- Remove the screw that secures the diode trio and remove diode trio.
At this point, test the rotor, rectifier bridge, stator and diode trio if these tests are necessary.
- Remove the rectifier bridge hold-down screw and the BAT terminal screw, then disconnect condenser lead. Remove rectifier bridge from end frame.
- Remove the two securing screws and brush holder and regulator assemblies. Note the insulating sleeves over the screws.
- Remove the retaining screw and condenser from the end frame.
- Remove the slip ring end frame bearing, if it is to be replaced, using the procedure given later in this section.
- Remove the pulley nut, washer, pulley, fan and spacer from the rotor shaft, using a 5 / 16 in. allen key to hold the shaft while loosening the nut.
- Remove rotor and spacers from drive end frame assembly.
- Remove drive end frame bearing retainer plate, screws, plate, bearing, and slinger from end frame, if necessary.
- To assemble, reverse order of disassembly. Pulley nut must be tightened to 40-50 ft. lbs.
CLEANING & INSPECTION
- Clean all metal parts, except stator and rotor assemblies, in solvent.
- Wipe off bearings and inspect them for pitting or roughness.
- Inspect rotor slip rings for scoring. They may be cleaned with 400 grit sandpaper (not emery), rotating the rotor to make the rings concentric. Maximum out-of-true is 0.001 in. If slip rings are deeply scored, the entire rotor must be replaced as a unit.
- Inspect brushes for wear; minimum length is 1 / 4 in.
ALTERNATOR COMPONENT TESTING
See Figure 9
Attach one lead of a 110 volt test lamp or an ohmmeter to either slip ring, and the other lead to the rotor shaft or poles. A lighted test lamp or low ohmmeter reading indicates grounded field windings.
Attach the lamp or ohmmeter connections to each slip ring. The windings are open if the lamp fails to light or the ohmmeter reading is high.
Connect a 12 volt battery and an ammeter in series with the slip rings to check for shorts. The windings are shorted if the reading exceeds 1.5 amps. An ohmmeter may be substituted for the same check and will show a resistance reading of less than 6 ohms if the windings are shorted.
See Figures 10 and 11
Attach the test lamp or ohmmeter to the stator frame and one of the stator leads. A lighted lamp or low resistance reading indicates grounded windings.
Successively connect the test equipment between each pair of stator leads. Open windings will produce a high resistance and prevent the test lamp from lighting.
Shorts require special test equipment. If all other tests fail to locate the problem, it is more than likely a short in the stator.
Separately Mounted Diodes (Pressed-in Type)
See Figure 12
The diodes may be checked for shorts or opens by using an ohmmeter or a 12 volt test lamp.
Use a 1 1 / 2 volt cell ohmmeter that has been adjusted to the lowest range scale. Attach one lead to the heat sink and the other to the diode lead. A good diode will show a high and a low reading depending on the connection switch. Two low or two high readings signal a faulty diode. Check the other diodes in the same manner. When servicing "perforated case" models, repeat this for the diodes in BOTH heat sinks.
Check the end-frame mounted diodes by connecting one test lead to the frame and the other to the diode lead. Reverse the connection and check the readings. The same diagnosis is true here as for the heat sink diodes.
If an ohmmeter is not available, substitute a 12 volt test lamp. Connect and switch connections in the same fashion as with the ohmmeter. The lamp will light in only one direction. If it lights or fails to light in both directions, the diode is bad.
Diode Rectifier Bridge
See Figure 13
Refer to the accompanying illustration for component identification. Use a self-powered ohmmeter set on its lowest reading scale.
Connect one ohmmeter lead to the grounded heat sink. Connect the other lead to each of the three rectifier bridge terminals (one at a time) and note the ohmmeter readings (1st set). The readings at each of the bridge terminals should be virtually identical. Reverse the ohmmeter leads and repeat the test, again noting the meter readings (2nd set).
Connect one ohmmeter lead to the insulated heat sink. Connect the other lead to each of the three rectifier bridge terminals (one at a time) and note the ohmmeter readings (3rd set). Reverse the ohmmeter leads and repeat the test, again noting the meter readings (4th set).
Readings taken for any one full set should be virtually identical, conversely, if you get two different readings WITHIN the same set, replace the rectifier bridge assembly. When comparing readings between sets 1 and 2, one set should read high, the other low. When comparing readings between sets 3 and 4, again, one set should be high, the other low.
See Figures 14 and 15
INTERNAL COMPONENT REPLACEMENT
Despite rumors to the contrary, diodes of this type may be replaced. It is not necessary to replace the entire generator assembly as some unscrupulous garage owners convinced their unwary customers in the introductory days of the AC generator.
Two types of diodes, positive and negative, are used in the AC generator. The heat sink contains the positive diodes and these are marked with red. End frame diodes are the negative ones and they have black markings. Do not attempt to drive a diode from its bore or the other diodes may be damaged.
Support the end frame in an arbor press, select a suitable removal spacer, and press the diode from the frame. Use the same method to install a replacement diode.
To replace heat sink diodes (which includes all of the diodes of "perforated case" models), it is necessary to separate the heat sink from the frame. Observe the stack-up closely to ensure correct reassembly of the BAT and GRD terminal bolts. Replace the diodes as described above, reassemble the bolt stack-ups and attach the heat sink to the end frame.
The drive end frame bearing is removed by detaching the retainer frame from the end plate and pressing the bearing out. Fill the bearing 1 / 4 full with multipurpose grease; do not overfill. Press the bearing into the end frame. Install the retainer plate.
The slip ring end frame bearing of the 6 in. "perforated-case" generator is pressed off the rotor shaft. The replacement is pressed over the rotor shaft by using an arbor press.
The 5.5 in. aluminum Delcotron slip-ring end bearing is replaced by pressing it out towards the inside of the case. To install the replacement, position a flat plate over the bearing and press it into the outside of the case. Press all bearings and diodes flush with their receptacles.
Brush and Holder
See Figures 16 and 17
It is always easier and worth the minimal extra cost to replace the brushes with their holder. For some models, brushes themselves are not serviced separately.
For externally regulated models, except the "perforated case" Delcotron:
- Remove the stator lead nut that also holds the relay terminal connector.
- Remove the two mounting screws and the brush holder assembly.
- When installing the new brush holder assembly, depress the brushes and insert a straightened paper clip through the holes provided in the holder for brush retention.
- Install the brush holder assembly.
- Remove the paper clip after the alternator is assembled.
For externally regulated models of the "perforated case" type:
If the alternator was disassembled according to the previous procedure, just install the new brush holder during assembly. If the alternator has not yet been disassembled, refer to steps 1-4 and 12e of the previous Disassembly and Assembly procedure to replace the brush holder. For internally regulated Delcotrons:
This procedure also includes replacement of the internal voltage regulator.
- Remove two brush holder screws and stator lead to strap nut and washer, brush holder screws and one of the diode trio lead strap attaching screws.
The insulating washers must be replaced in the same position on reassembly.
- Remove brush holder and brushes. The voltage regulator may also be removed at this time, if desired.
- Brushes and brush springs must be free of corrosion and must be undamaged and completely free of oil or grease.
- Insert spring and brushes into holder, noting whether they slide freely without binding. Insert wooden or plastic toothpick into bottom hole in holder to retain brushes.
The brush holder is serviced as a unit; individual parts are not available.
- Reassemble in reverse order of disassembly.