The gear on the end of my speedometer cable, the end that fits into the transmission, has 18 teeth on it. My speedometer reads about 10 MPH under. When the speedometer reads 50 MPH, the car is going about 60 MPH. I know I need to change the gear but should I go down to a 16 tooth gear or up to a 21 tooth gear to get my speedometer to read closer to the true speed the car is traveling?

I'm driving a early 65 D Code Mustang, 289 4V with a C4 Auto and a 3.00 rear and 195R75x14 tires.

Thanks

 

To speed up the speedometer, go to a smaller tooth driven gear. To calculate, you need 1000rpms on the speedometer cable at 60mph. According to my calculator, you need about a 16.6 tooth gear...so a 17.

 

Thanks, I'll give it a try and let you know after I get the gear and install it.

Tom