Pschimmel,
I am by no means an Hammond player, but I remember that once a friend of mine, who owned a real Hammond C3 (a beast, who took one fourth of his living room) told me that, to make the beast "scream" the way Jimmy Smith does, you have to use the volume pedal in a very particular way, kicking it almost all the way down while you "stab" a chord (Jimmy Smith uses 13th chords to do that) and immediately relieving the pressure (it should be a short scream, not a deafening, sustained tone).
You can hear examples of this technique in almost all uptempo Jimmy's tunes (like "The cat"), particularly when he is improvising.