I had to change the stock speedometer in my 56 for another one. The old one would suddenly go bonkers and zoom up to 90-100 mph. I put another TF speedometer in and it is now 10 mph slow at 70 mph. In other words, when I'm doing 70, it registers 60. Old speedo was dead on, just erratic sometimes. New gears, cale, etc. Any ideas what is causing the difference, or what is my best solution? Again, only change is in speedometers.
