I changed the rear end in my 68 coupe years ago and the speedometer was always way off. It is a 3:5 to 1 with standard 14 inch tires. The problem is when I am doing 45 by the speedometer I am really doing 65. At 50 it is really 70 and at 60 it is really 85. I replaced a 16 tooth speedometer gear with 19 tooth and it is worse. How can I figure this out? Do I need more teeth or less?