1990 535i M alternator

[kiNGMak]

How do i tell which alternator i need? i cannot find a part number on it.. and i do not want to take it off the car till i get the new one.. BMW and BMA advise that there is 2 different types.. a 115 and a 90... build date of the car was in March of 90

[Dash01]

There should be an orange sticker on the outside of the alternator, which you can read on the car by use of a small mirror + flashlight.

New alternators are very expensive for these cars. So, I rebuilt mine:

1. Brushes are the most common failure, and can be replaced for several dollars at any decent auto parts store. Regulator assy comes next, and includes brushes. This will cost ~$13-~$50, depending on source. These first two items can be replaced without removing the alternator from the car, but make sure to disconnect the battery first, being sure you have the radio anti-theft code handy.

2. Bearings can run ~$25+ at auto parts stores, but I found equivalent or better sealed bearings at a farm implement (Case, John Deere, etc.) store for ~$3 to $4 each. (Take the old bearings in so they can read the part number for cross-reference.)

3. Finally, the diode plate may require replacement. The only way to test it is to de-solder & remove it from the casing. These are hard to find, but a friend of a friend in the auto electrics business got me one for ~$35.

4. Steps 2 and 3 above will require dis-assembly of the alternator, pulling the bearings, etc. Any decent auto shop can do this for you, drop off and pick up later, for a few dollars.

5. eBay has Bimmer alternators frequently, but you never know if the one you get is really any better than your old one, and my not even fit. Personally, I'd do step 1 above, and if that did not work, do steps 2 and 3 in one fell swoop.