BMW Coupes and Sedans 1970-1988 Repair Guide

Alternator

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PRECAUTIONS



Several precautions must be observed with alternator equipped vehicles to avoid damaging the unit. They are as follows:



If the battery is removed for any reason, make sure that 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 it as follows: positive to positive, and negative (booster battery) to a good ground on the engine of the car being started. Note that on the 1982 733i, the No. 5 fuse must be pulled out of the fuse panel before using a booster battery, or the inboard computer may be damaged.
 
Never use a fast charger as a booster to start cars with alternating-current (AC) circuits.
 
When servicing the battery with a fast charger, always disconnect the battery cables.
 
Never attempt to polarize an alternator.
 
Avoid long soldering times when replacing diodes or transistors. Prolonged heat is damaging to alternators.
 
Do not use test lamps of more than 12 volts for checking diode continuity.
 
Do not short across or ground any of the terminals on the alternator.
 
The polarity of the battery, alternator, 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.
 
Turn OFF the ignition switch and then disconnect the battery terminals when performing any service on the electrical system or charging the battery.
 
Disconnect the battery ground cable if arc welding is to be done on any part of the car.
 

CHARGING SYSTEM TROUBLESHOOTING



There are many possible ways in which the charging system can malfunction. Often the source of a problem is difficult to diagnose, requiring special equipment and a good deal of experience. This is usually not the case, however, where the charging system fails completely and causes the dash board warning light to come on or the battery to become dead. To troubleshoot a complete system failure only two pieces of equipment are needed: a test light, to determine that current is reaching a certain point; and a current indicator (ammeter), to determine the direction of the current flow and its measurement in amps.

This test works under three assumptions:

  1. The battery is known to be good and fully charged.
  2.  
  3. The alternator belt is in good condition and adjusted to the proper tension.
  4.  
  5. All connections in the system are clean and tight.
  6.  

In order for the current indicator to give a valid reading, the car must be equipped with battery cables which are of the same gauge size and quality as original equipment battery cables.

  1. Turn OFF all electrical components in the car. Make sure the doors of the car are closed. If the car is equipped with a clock, disconnect the clock by removing the lead wire from the rear of the clock. Disconnect the positive battery cable from the battery and connect the ground wire on a test light to the disconnected positive battery cable. Touch the probe end of the test light to the positive battery post. The test light should not light. If the test light does light, there is a short or open circuit on the car.
  2.  
  3. Unfasten the voltage regulator wiring harness connector at the voltage regulator. Turn ON the ignition. Connect the wire on a test light to a good ground (engine bolt). Touch the probe end of a test light to the ignition wire connector into the voltage regulator wiring connector. This wire corresponds to the I terminal on the regulator. If the test light goes on, the charging system warning light circuit is complete. If the test light does not come on and the warning light on the instrument panel is on, either the resistor wire, which is parallel with the warning light, or the wiring to the voltage regulator, is defective. If the test light does not come on and the warning light is not on, either the bulb is defective or the power supply wire form the battery through the ignition switch to the bulb has an open circuit. Connect the wiring harness to the regulator.
  4.  
  5. Examine the fuse link wire in the wiring harness from the starter relay to the alternator. If the insulation on the wire is cracked or split, the fuse link may be melted. Connect a test light to the fuse link by attaching the ground wire on the test light to an engine bolt and touching the probe end of the light to the bottom of the fuse link wire where it splices into the alternator output wire. If the bulb in the test light does not light, the fuse link is melted.
  6.  
  7. Start the engine and place a current indicator on the positive battery cable. Turn off all electrical accessories and make sure the doors are closed. If the charging system is working properly, the gauge will show a draw of less than 5 amps. If the system is not working properly, the gauge will show a draw of more than 5 amps. A charge moves the needle toward the battery, a draw moves the needle away from the battery. Turn the engine OFF .
  8.  
  9. Disconnect the wiring harness from the voltage regulator at the regulator at the regulator connector. Connect a male spade terminal (solderless connector) to each end of a jumper wire. Insert one end of the wire into the wiring harness connector which corresponds to the A terminal on the regulator. Insert the other end of the wire into the wiring harness connector which corresponds to the F terminal on the regulator. Position the connector with the jumper wire installed so that it cannot contact any metal surface under the hood. Position a current indicator gauge on the positive battery cable. Have an assistant start the engine. Observe the reading on the current indicator. Have your assistant slowly raise the speed of the engine to about 2,000 rpm or until the current indicator needle stops moving, whichever comes first. Do not run the engine for more than a short period of time in this condition. If the wiring harness connector or jumper wire becomes excessively hot during this test, turn OFF the engine and check for a grounded wire in the regulator wiring harness. If the current indicator shows a charge of about three amps less than the output of the alternator, the alternator is working properly. If the previous tests showed a draw, the voltage regulator is defective. If the gauge does not show the proper charging rate, the alternator is defective.
  10.  

REMOVAL & INSTALLATION



1970-81 Models

See Figure 1

  1. Disconnect the negative battery cable, then the positive battery cable. On some models, it may be necessary to remove the battery for alternator removal clearance.
  2.  
  3. Remove the stabilizer bar, if necessary on 2002Tii models.
  4.  
  5. Mark any individual electrical leads that could be installed to the wrong terminal during reinstallation. Then, pull off any multiple connectors, To disconnect individual leads, remove the rubber covers, then the attaching nuts, and pull the leads off.
  6.  



Click image to see an enlarged view

Fig. Fig. 1: An alternator as installed on a 2002

  1. Remove the bolt which runs in the slotted adjusting bar and loosen the mounting bolt. Slide the unit toward the engine, remove the adjusting bolt and the main mounting bolt and detach the alternator from the engine.
  2.  

To install:
  1. Locate the alternator in its normal position and install the main mounting bolt loosely.
  2.  
  3. Install the fan belt onto the alternator pulley. Position the sliding bracket appropriately and install the mounting bolt for that bracket. Finally, tension the fan belt.
  4.  
  5. Fasten all electrical connections.
  6.  
  7. Install the stabilizer bar and/or battery if removed. Reconnect the battery cable(s).
  8.  

1982-88 Models

See Figures 2, 3 and 4

  1. Disconnect the negative battery cable followed by the positive cable.
  2.  
  3. Disconnect the wires from the rear of the alternator, marking them for later installation. Note that there is a ground wire attached to the alternator on some models.
  4.  
  5. Unscrew the nut and loosen the hose clamp around the airflow sensor. Unfasten the plug attached to the sensor. Then, lift out the air cleaner and airflow sensor as a unit.
  6.  



Click image to see an enlarged view

Fig. Fig. 2: Loosen the bracket bolt from the engine block to the upper portion of the alternator



Click image to see an enlarged view

Fig. Fig. 3: On star bolts, after the locknut has been loosened, use two wrenches to remove the bolt



Click image to see an enlarged view

Fig. Fig. 4: Remove the bolt from the lower portion of the alternator

  1. Loosen the adjusting and pivot bolts, and remove the V-belt.
  2.  

If the alternator has a star tensioning bolt, loosen the lockbolt, turn the tensioning bolt so as to eliminate belt tension and then remove the belt.

  1. Remove the bolts and remove the alternator. On 633CSi, 635CSi, 733i and 735i models, it may be necessary to loosen the fan cowl to get at the mounting bolts. On 535i models, it may be necessary to disconnect a power steering line that runs near the alternator.
  2.  

To install:
  1. Position the alternator into position and install the mounting bolts. Install the nuts, and tighten by hand.
  2.  
  3. Install the necessary wires to the alternator. Do not forget to install the ground wire to the alternator body, if equipped.
  4.  
  5. Adjust the belt tension to approximately 0.4 inches (9mm), measured between the balancer and the alternator pulley.
  6.  
  7. On some 1984-88 models, a star bolt is used to adjust the belt tension. The tensioning bolt on the front of the alternator must be turned to tension the belt. Use a torque wrench, until the torque is approximately 5 ft. lbs. (6 Nm). Then, hold the star bolt with a wrench while tightening the locknut at the rear of the unit.
  8.  
  9. When the belt is tensioned to specification, tighten the remaining retainer bolts
  10.  
  11. Install the air cleaner and airflow sensor if removed. If the power steering line had to be disconnected, reconnect it securely, refill, and bleed the system.
  12.  
  13. Connect the negative battery cable followed by the positive.
  14.  

 
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