1962 C10

When I bought this truck the speedo cable was squeeking so bad that I had to pull over and disconnect it from the gauge itself. The needle was bouncing all over the place and screaming something horrible. Is the gear stripped out in the gauge itself or what else could it be.

The guy I bought this truck from said they had the fuel tank sealed a few years back. I just noticed that the fuel gauge is not working. I looked behind the seat and the wiring "looks" correct but who knows. How is the best way for me to tackle this fuel gauge not working problem??