My needle was jumping pretty bad for a while on my '90. When I was doing 35mph, the speedo needle bounced between 30 and 40 mph. I pulled the cluster, unhooked the speedo cable, used some needle nosed pliers and pulled the metal cable out to where it stuck out about 1/2" past the end of the cable end attachment (white plastic part on the end) and re-installed it. For whatever reason, my speedo is now smooth as new. Obviously, this won't help you if you have a '91 or newer but it's worth a try (and free!) if it's older.