Charging voltage test
Usually the generator does not require repair, except for the really rare cases of replacing the generator brushes. More severe damage cannot be repaired with home remedies.
Connect a voltmeter between the thick red wire terminal of the generator and «weight».
Leave the engine running at medium speed.
If the voltage regulator is working, the voltmeter should show between 13.3 and 14.6 V.
If not, check the brushes or replace the regulator.
Otherwise, the generator itself is faulty.
Checking the brushes
Disconnect the negative battery terminal.
Bosch alternators: remove the cover on the battery at the back (where available).
Disconnect the regulator from the generator. To do this, remove two screws.
Left: for removing the cover (2) Bosch alternator, you need to unscrew the three Phillips screws (1), remove the B+ wire from the threaded bolt (3) and press out the fasteners (arrows).
Right: voltage regulator (2) fastened with two cross-head bolts (1). Position (3) denotes the axis of the generator rotor.
Left: on the removed voltage regulator (4; the illustration shows the new design) brush length (2) marked with arrows. Position (1) shows the contacts of the voltage regulator, (3) are the fixing bolts.
Right: The illustration shows the measurement of the length of sliding electrographite contacts on a removed Bosch voltage regulator of an older design: the brushes must not be shorter than a = 5 mm.
Swing out the regulator so that the carbon brushes do not hang down.
Measure brush protrusion:
- length of new brushes 13 mm;
- minimum length 5 mm.
Valeo alternators: Unscrew both fixing screws of the regulator on the back of the alternator.
Pull out the regulator.
Measure the length of the protruding brushes.
If the remaining length is 5 mm, the brushes are worn out.
Valeo alternator brushes cannot be purchased separately; the entire regulator needs to be replaced.
Brush replacement
Replacement of brushes on regulators of the new generation of generators from Bosch is no longer possible - therefore, carbon brushes are no longer sold as spare parts. If they are worn out, the entire regulator should be replaced. The same can be said about the Valeo generator; carbon brushes are not sold as a spare part - you need to buy a new voltage regulator if the brushes of the old one are worn out.
However, for Bosch generators of the old generation, such a replacement is possible. This will require a soldering iron, solder and, in addition, the ability to work with them.
Remove the voltage regulator as described above.
Unsolder stranded flexible wires, pull out carbon brushes.
Remove pressure springs from old brushes and put on new ones.
Solder stranded flexible wires.
At the same time, use a little tin and work quickly so that the wires do not suck in a lot of tin. Otherwise, they will become rigid.
Hint: if the brushes are removed, you can check the copper slip rings at the same time (brushes go over them). If deep traces of running-in were found on them, then they need to be turned and polished in an auto electrician workshop.
Disconnect wire «masses» from the battery, otherwise there is a high risk of a short circuit.
Models with 4-cylinder engines: remove cover (where available) pivot bolt on the front of the toothed belt guard.
Disconnect the cable to «mass», where available.
Loosen the clamping bolt on the alternator adjusting bar.
Disconnect connecting wire.
Loosen and remove the V-belt or V-ribbed belt.
Loosen and remove the pivot bolt while holding the alternator.
Models with 5-cylinder engines: remove the lower protection of the engine compartment.
Disconnect connecting wire.
Remove fixing bolts, remove alternator.
Models with 6-cylinder engines: remove the lower protection of the engine compartment.
Remove V-belt (job description later in this chapter).
Remove the connecting wire and the cooling air guide from below.
Loosen the mounting bolts, remove the generator.
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