My speedometer did something funny today. I was driving, first thing in the morning, and my speedometer started to sound like a wind-up toy, then shot up to 90 mph (I was going about 35). What causes this, and what is the cure?
It sounds like you have a cable driven speedometer and that it is time to check it. Make sure both ends are tight and that it is lubed. Next step is to replace the cable.