E30 BMW Alternator Replacement

The battery in my 1987 325is has been losing its charge recently. It left me stranded at work a few weeks ago. It problem was diagnosed as a bad alternator. with the car on the battery was not being charged. This meant the car was basically running off the battery. Eventually the battery gets so low that the car cannot run properly . Dim lights, rough running, and no accerosires are common symptoms, The alternator had been replaced once before several years ago by my brother, luckily the alternator had a lifetime warranty through AutoZone so it cost me nothing.

First gather your tools:

Then raise and properly support your car:

Remove the air box so that you can access the alternator:

Remove the rubber covers that protect the two terminals on the back of the alternator:

loosen the two bolts that hold the alternator on. One is at the top, the other on the bottom, take off the belt and remove the alternator:

Here the alternator has been taken out of the car and all the components on the back can be seen:

Remove the clip and radio noise suppressor(black square with wire coming out of it):

And transfer them to your new alternator, along with the pulley and fan (done for me at AutoZone):

Place your new alternator in the bracket, install the bolts and slip on the belt:

Reattach wires and slip on covers. Place wires in the wire clip:

Install airbox:

Check voltage with car running. A voltage around 14 is good:


4 thoughts on “E30 BMW Alternator Replacement

  1. Thanks so much for posting this. The manuals cover the basics, but they leave out a lot of details. Can you answer a few other questions?

    1. Would you describe and/or write up instructions on how to remove the air box and how much of it did you remove?

    2. In order to remove the the alternator, especially the bottom bolt, is it necessary to work from underneath the car? I see no way to even see, let alone *reach* the lower bolt. In fact, even the wiring terminals seem hard to reach since the alt. is placed so low in the engine compartments. Please comment. The job seems simple enough, but accessing hard to reach areas without super long arms appears to be the dirty little secret. Or at least a hard trick.

    If you could email me at the supplied address, I would appreciate it, so that I might be able to email you directly (and quickly) with responses.

    • I did this at least 6 years ago, so the details are a little hazy.

      1. There should be two nuts on the side. You’ll have to loosen the intake boot clamp and remove the MAF wiring connector too. It will pull straight up.
      2. I do seem to remember getting some of the bolts from the bottom, putting my arm up in between the block and steering column shaft.

      • “I did this at least 6 years ago, so the details are a little hazy.”

        Hmm… it seemed like since the post was in 2009, that you had actually done it about that time. Do you still own the car?

        Regarding the new alternator voltage output…. I had someone replace mine since I was too chicken and unprepared to try it myself, and the voltage at idle with no accessories is about 13.5-13.6. When I start to turn on accessories, it steadily drops to a final number of about 13.2. Then, running at 1500+ rpm and measuring from the cig lighter, the voltage does not increase with engine revving. It stays around 13.2 with all the stuff turned on and engine speed.

        Q: Does this sound to low to you or do you think it is ok? I’m impressed that you got 14v out of yours. Did yours go down when you turned on the headlights and a/c ?

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