Oh Those Knobs!

I've forgotten how to release and remove the heater temp knob and defroster knob from their shafts. This is a '69 B with plain black knobs, not like the earlier ones with a chrome center cap. I know it isn't done with an allen wrench, and not done with a screwdriver. I also had no luck with depressing what must be a spring loaded ball bearing down inside that little access hole. What gives? Does the knob have to be in a certain position? I'm stuck, sure don't want to ruin them, but I need to remove them. Any insight on this would really be appreciated. Thanks guys.
Pete

I found the answer. It is a pressure deal as I thought I remembered it. Insert a pick or an undersized allen wrench, press down on spring loaded dog pin and remove knob. The first knob I was working on was installed by PO with epoxy putty, the second one was proper. Wish I had started with the second one first. Well time to call "Vicky" again
Pete