Bad speedo or cable?

[wcorbett]

Now that I'm driving the truck more regularly, some age issues are popping up. Occasionally heard a a noise that was behind the dash intermittently. Driving down the road today, suddenly a high pitch squeal under my feet, speedo was bouncing at the 100 mph mark( no I wasn't actually going that fast), stopped the truck, and the speedo stayed pegged past 100. Disconnected the cable at the trans first ( no change), then disconnected behind the dash (no change). Speedo is now pegged all the way to the right. So, is the speedo toast, or can I reset it somehow and replace the cable and be good to go? Thanks for any help?