if you have got about 150k miles or so, then the wear to the commutator is probably excessive. i have cut them down on a lathe and polished, put in new brushes... you wil bo o.k. for a few months. It about time for a new commutator... thats a lot of work, just get another alternator. You can get a better deal than $300. I bought a takeoff on e-bay from a guy that builds ambulance and puts on BIG units. It cost me about $100. a couple years ago.