dont do what he just said. that wouldn't cause a "bouncy" speedo. it's something called the speed sensor. it's what the speedo gear clips on to and what the speedo cable plugs into. it's kind of like the middle man. it's located on the driver's side of your transmission towards the top. you can get them at autozone or something for like $30-$40. mine used to do the same thing but only up to liek 15-20mph