Sponsored Links (Register now to hide all advertisements)
As Neil asks above, you may have the wrong gear in the drive. I suggest you go for a drive - the longer the better and check the distance in your modern car. If the Model A odometer gives the same reading as the modern, it is the speedo part of your instrument that is doubtful. If the distance is different by about the same 9%, it is the drive gear at the bottom end of the cable. Change it (probably by 2 teeth) and you'll be good.
You didn't say whether your speedo was reading high or low so I can't say whether you need more or less teeth on the drive gear. If it is reading slow, you need 2 less teeth. If it is reading fast, 2 less. If you change the gear, be careful to put the new one on facing the same way as the old one was.