The gauge cluster in my 56 F100 keeps crapping out. I have had the orginal and one other that worked for a time and have now stopped. The 2nd one I could spin by hand and see the needle raise, but now does nothing. Before I buy another one, I wanted to know if the cable could be at fault so I don't smoke a 3rd. The cable is connected to a C6, just in case it matters.
Did you make sure the cable was lubed? If they dry out they can cause the needle to bounce. I think it's unlikely that you broke the speedo head.
I had the cable bind back when I was a kid. It twisted the cable off AND siezed up the speedo. I learned, got another cable and speedo AND lubed 'em once in a while. Sometime, I'll find the old speedo and see if it can be resuscitated or torn down and rebuit. Not a big deal right now. I think newer cars went to electronic speedometers. But what fun is that?
Its at a friends shop for some body and paint work. For the time being I see it on Sundays and work on it. Trying to get it ready for the Roundup