Regarding rebuilding alternators -- There are two bearings, one at each end, and two brushes which ride on "slip rings"; on the spinning part. There should be a brush-block on the side or top which may be removable so you could see the state of the brushes (the old style generator brushes are replacable in the car, but I haven't had a REAL close look at the alternator). Alternator brushes wear much slower that generator brushes, so it may just have a slow deterioration of these. If they are worn, also check that the slip rings aren't too worn down into "valleys" where the brushes ride. If this happens the alternator would definitely need to go to an overhaul place to have the rings machined or replaced - so new brushes will ride properly.
According to "Speedy Jim", re-building alternators is quite a chore, and it may be difficult getting the proper bearings. Jim says he would opt for a rebuilt unit if it's bad.
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Last revised 4 May 2004.