the pulley that provides tension for the alternator has come off its
bearing. since i have never taken off this pulley before, i do not know if
it is broken or if some kind of "gasket" has worn off the bearing. if the
bearing was pressed on to the pulley, then there must be some kind of
rubber, (or some other material) gasket in-between to provide the friction
to keep the pieces together.
Are you sure you're not talking about the pulley that tensions the Air
Conditionion belt? It has a pulley in the middle that tensions things.
They go bad, and all you need to do is order a new one. I think I
paid almost $90 for mine back when AlfaBill was still supplying OEM Alfa
bits. (The AC pump is on the passenger side of the engine compartment.)