Brushes and Voltage Regulator

The brushes contact the alternator's slip rings to supply the current that magnetizes the alternator rotor. The voltage regulator maintains a nominal voltage in the electrical system by feeding excess output from the alternator back to ground. In addition, it regulates the amount of current supplied to the alternator rotor, turning it on and off as needed. If either component is faulty, the result will be an over or undercharged battery. The brushes wear under normal use, and will eventually need to be replaced.

Fig. 5-3.

Tensioning alternator V-belt on models without toothed rack adjusting mechanism. Mounting bolts (arrows) should be loose before adjusting tension. Dimension A should be between 2 mm and 5 mm (5/64 in. and 3/16 in.)

The brushes and regulator are mounted on the rear of the alternator and can be replaced with the alternator installed. The regulator and brush holder is removed by removing two screws. Check the brush length as shown in Fig. 5-4. On some alternator models the brushes are available as separate parts; on others they can only be replaced with the regulator. See an authorized Volkswagen dealer parts department for more information.

Fig. 5-4.

Alternator brush length being checked. Length a of new brushes is 13 mm (17/32 in.). Replace brushes worn to 5 mm (7/32 in.) or less. Regulator and brush holder shown is used on Bosch alternators, Motorola is similar.