Speedo bounce

I have a 94 nissan pickup. The speedo needle doesn't go below 30mph and when I start to go it jumps all the way to peg high most of the time. Sometimes it works its way up to around 90mph. I don't need to be going very fast for this to happen. Sometimes while I am driving down the highway it sits around 80 to 90 mph but it is mostly peged high. Does anyone know what this is caused by?

dry or dirty speedo cable also check it for being loose...

Thank you for your reply. I found out that it is the speedo itself. I replaced the speedo cable first and that did not fix it so I had the speedo replaced and that took care of the problem.

aschurkamp (http://www.automotiveforums.com/vbulletin/member.php?u=623694),

My 93 is doing the same thing and I've read about that being the most common solution, A lot of people seem to be needlessly replacing the speedo cable as a first, more cost effective solution.

What did the parts run you for the speedo? They replaced the entire cluster? Does your odometer read the same or is it zero now?

Thanks, Mike