Not the alternator but the starter. If it is carbon brushes that are almost worn out, knocking the starter might work. If it is a bad terminal connections, bad ground, wiring fault or the security system, it is not going to work.
October, 14, 2012 AT 6:53 PM
Yeah that's what mechanics do, ... Hit things with hammers to make 'em work. In school we teach them to know WHERE to hit things.
Please provide some details. How do you know the battery is fine? Did you measure its voltage? Do the interior lights work. The generator has nothing to do with cranking the engine so why is that on your list of suspects? Have you checked the battery cable connections? What other symptoms do you observe?
October, 14, 2012 AT 7:01 PM
As a side note, GM redesigned their generators and starters for the '87 model year. The generators cause a REAL lot of trouble but the starters are pretty reliable, AS LONG AS YOU DON'T HIT THEM! GM trainers warn against that because instead of field coils of wire they use permanent magnets that are glued to the case. Banging on it will break them loose destroying the unit. At that point it can't be rebuilt either so it's worthless for a core return. Even the training video warns against hitting them. That will turn a starter that is most likely okay into one that may be junk; then you'll have two problems.