Since I do not have a bernina machine I can only talk about what I see and what you are telling me. First of all the 2 pictures that have been posted the 2 walking feet are not the same. The fork in the first one appears to be shorter. I sell Viking machines and there are several walking feet for their machines and it sounds as if as you are saying that the needle broke and you changed it and then the walking foot would not say on the needle bar. If your machine needle vibrates when you turn on the machine it means that you have a computerized machine and it is calibrating the needle. This could be the reason that the fork is falling off of the needle bar. If this is always happening when you are turning on the machine then it sounds like you have the wrong foot for your machine.