There is a cross pin on the yoke and it is probably missing,remove the mechanical plate through the front or just the yoke if you want,drive out the broken pin and replace it with one made from brass rod . You can see the pin in the patent drawing but it gets lost in the lines of the drawing....Email me if you have questions Jarg1@gwi.net,I also have material for the horn and supple leather for the bag bellows....Regards John Richardson jargo