Speedometer Driven Gear Type 3A 19-Tooth Mustang With 4-Speed Toploader Transmission 1965-1973

Today we're going to show you how to correct the speedometer in your 1964 through 2014 Mustang. If you own a 1964 through 1998 Mustang, your speedometer is going to be calibrated mechanically using a drive gear and a driven gear. The driven gear mounts on the end of the speedometer cable, and is going to go in the side of your transmission. The drive gear mounts on the tail shaft, spins the driven gear, which turns the cable and spins your speedometer.
These are the two styles of driven gears that are available. The gray gear is a type three gear, which is a right-hand rotation designed for transmissions where the cable enters on the left side of the transmission.

This here is a type three A with a left hand rotation. This will be used with transmissions where the cable enters on the right hand or passenger side of the transmission. The drop gear shown here is available in six, seven or eight tooth varieties. When paired with one of the speedometer gears it can pretty much come with any gear ratio necessary to get your speedometer pretty close. The driven gears are available from 16 tooth all the way up to 23. There is a mathematical formula you use to determine which driven gear you need based on what drive gear you are using.

What you'll want to do is take the drive gear teeth times that by the axle ratio of your car. If there are 373 gears you'd times it by 3.73 and you would times that by the tire revolution per mile, which you would be able to get off the manufacturers site for the tires you currently own. You times those three numbers together, divide by 1001 to determine which driven gear you need.

This is a speedometer gear retainer. This actually holds the driven gear to the speedometer cable itself. When ordering a new gear, it's never a bad idea to order a new retainer, as well. If you own a 1999 through 2014 Mustang you'll have to recalibrate your speedometer electronically. For 1999 through 2008 manual transmission cars you can use a speedometer calibration box here. Inside the box is a series of dip switches that you adjust to correct for speedometers. Again, this will only work on your 1999 through 2008 manual transmission. It will not work on an automatic.

For all 1999 through 2014 Mustangs the other option is going to be the X-Cal custom tuner. This will not only give you performance benefits, it allows you to calibrate your speedometer as well as your revolutions per mile to get the electronic speedometer perfectly adjusted.

Remember both gear changes, as well as tire changes, have an effect on your speedometer so you'll want to adjust accordingly. Using the drive gear and driven gear you'll be able to adjust from anywhere from a 273 gear all the way up to a 456. With electronic speedometers, it's pretty much infinite as far as the amount of adjustment.