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Thread: Alternator troubles

  1. #1
    Join Date
    Mar 2004
    Location
    Brisbane, Australia
    Posts
    418

    Default Alternator troubles

    Recently the battery light on my dash has started glowing extremely faintly, almost impossible to see untill in total darkness. Obviously this is starting to affect the performance of the battery. Problem is, the light only comes on sometimes. When the light is on, the voltage output of the alternator is reading 12.05V and when it's off it's reading around 13V give or take a bit. Could this be a fuked voltage regulator or does the alternator just need a rebuild? .

  2. #2
    Join Date
    Jul 2005
    Location
    Cologne, Germany
    Posts
    131

    Default

    worn carbon brushes i guess
    greets from Germany,
    Kai


    A BMW is a black car with most rights in road traffic.

  3. #3
    Join Date
    Mar 2005
    Location
    Bethlehem, PA
    Posts
    661

    Default

    With gradual degradation like that it's probably brush wear. It could also be a diode going bad or the regulator IC. You can replace the regulator and brush assembly, but if I were going to the trouble of accessing the alternator for this work, I'd probably just stick in a new rebuilt alternator if there's a lot of miles on the one that's failing. A rebuilt alternator will get you new bearings, slip rings, brushes, and regulator.

  4. #4
    Join Date
    May 2004
    Posts
    485

    Default

    If you're semi-handy with a soldering iron, you can replace the brushes for about $3, by removing the regulator from the back side of the alternator. Disconnect the battery first, keeping in mind that you'll then need the radio anti-theft code upon re-connection.

    Or, while you have the regulator out, just replace it for ~$13 at NAPA for a knockoff, or several times that for a Bosch original from BMA.

    I replaced my brushes and put the old unit back in about 15 months ago, with no ill effects. I keep a NAPA knockoff regulator in the glove box, as a backup.

  5. #5
    Join Date
    Mar 2004
    Posts
    454

    Default

    Quote Originally Posted by Dash01
    If you're semi-handy with a soldering iron, you can replace the brushes for about $3, by removing the regulator from the back side of the alternator. Disconnect the battery first, keeping in mind that you'll then need the radio anti-theft code upon re-connection.

    Or, while you have the regulator out, just replace it for ~$13 at NAPA for a knockoff, or several times that for a Bosch original from BMA.

    I replaced my brushes and put the old unit back in about 15 months ago, with no ill effects. I keep a NAPA knockoff regulator in the glove box, as a backup.
    Not to divert the thread, but did NAPA have the brushes?
    Thanks,
    Scott
    1995 BMW 525i w/139K miles, EAT Chip - (Gone)
    07 525i 22K, 07 328xi (41K)
    1982 Mazda RX-7 w/147K miles (Back again!)

  6. #6
    Join Date
    Mar 2004
    Location
    Brisbane, Australia
    Posts
    418

    Default

    Thanks. I'll get hold of some brushes and whack them in.

  7. #7
    Join Date
    May 2004
    Posts
    485

    Default

    Pretty sure it was NAPA that sold me the brushes, but they're pretty common brushes and probably can be bought from a hardware store, electrical shop, etc..

    I used the old springs, which had plenty of strength, esp. when fully compressed on installation of the new brushes.

    And, did not bother to contour the brush tips, since the alternator shaft acts as a lathe and does that when the brushes are installed.

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