1976 Chevrolet Cheyenne Broken speedometer

I can't remember exactly what year it is I'm pretty sure it's a '76 but I have a Chevy Cheyenne that has a broken speedometer, it stays at 0 mph all the time, how do I fix it? I don't want to have to replace it and from what I hear its not to hard on the older models like this cause they aren't to technologically advanced.