MyE28.com

I need a new one and can’t find a clear answer. What works?

90a unit with isolator bushings. used to be sold as Bosch AL140x. interchanges with E30 M3 and E24 M6, as well.

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if yours is in good, rebuildable condition, send it to a local starter and alternator shop in your area.

Thanks, any modification needed?

Slow down a minute. What is wrong and what have you done? Not a M guy, but I've never seen a regular E28 alternator fail. I'm sure some do, but rarely. Usually a no charge is a bad regulator, often as not just bad brushes. I'm guessing, but I don't know, M5s use the same regulator. They're cheap. Try a new one of them before a new alternator. On M30 cars at least, and I know M's are busier down there, on M30 cars it's a 5 minute changeout. Alternator might be bad, but try the cheap simple stuff first.

Disclaimer. I'm not a M guy. For all I know it might be a crazy water cooled alt like some E39s have. But I doubt it.

Some years ago the diode pack in my alternator failed.  It's available separately (or at least it was at the time) but requires disassembly of the alternator and some soldering.  I'm an electrical engineer and usually go the repair route, but I was real busy at the time and didn't want to wait for parts to arrive so I bought a rebuilt replacement alternator from the local auto parts store.  I don't remember exactly but I think I got it from Auto Zone.  the replacement was a Bosch, and it's worked fine ever since.