How to Remove the Alternator on a BMW 325

1. Disconnect the cable from the negative terminal on the battery. Locate the alternator, which is located on the front, left side of the engine and will have a belt attached to it and which drives it when the car is running.
2. Remove the belt that drives the alternator. Remove the small plastic cap that covers and protects the tensioner. Place the appropriately sized Allen tool in the tensioner and turn it clockwise or counterclockwise--the direction will vary, depending on the year of the car. Slide the belt off the tensioner once it is loosened and maneuver it out of the engine bay.
3. Unbolt the alternator from the pivot bracket with a socket and ratchet. Since the belt holds the alternator tight, it is only held on with one bolt on the pivot bracket. It is quite easy to remove.
4. Disconnect the electrical connections that are fastened to the rear of the alternator. Draw a diagram of how and where the wires are attached or take a photograph so that the wires are re-fastened to the back of the alternator in the correct orientation. If they are installed incorrectly, it could damage the electrical system.
5. Remove the nut that holds the pulley onto the old alternator. The best way to remove it is to use an impact wrench. Place the appropriately sized socket on the impact wrench and then spin the nut off with the impact wrench. Remove the pulley, install it on the new alternator and then install the nut back on with the impact wrench.
6. Reconnect all of the wires to the back of the alternator. Reinstall the alternator on the pivot bracket and tighten the bolt on the bracket. Reinstall the belt and the belt tensioner. Put the plastic cover back on the tensioner. Reconnect the negative battery cable.