How do I fix the agitator on my GE HotPoint washer?

The washer will fill, go through the cycle just fine but the agitator wont move. When I go to spin it, it spins freely, I know that isn't supposed to happen. We took it apart and if we lift the agitator just a little bit it catches on the grooves and is fine but once we screw it back together the part lowers and spins free again... could there be a washer or a rubber piece missing that's supposed to raise the mechanisim?