speedo trouble...need help

[Cifu]

I'm having issues w/my speedometer. It's simply not working. I have pulled it out, and examined several things. Speedometer cable turns when car is in motion (which logic would say that speedometer cable and angle drive are fine), please correct me if i'm wrong. When i connected the drill to the back of the speedo it seemed to trun slightly but appeared loose and wobbly behindd the metallic center cap. Planning on taking off glass and evaluate if loose or totally screwed. Any info on how to remove the glass? Any other suggestions or possibilities.

Thanks