How to correct your speedometer (and odometer) after changing your differential or transmission.
This writeup is meant to assist someone who is trying to correct their speedometer after changing their differential to a new final drive ratio, or after changing their transmission.Correcting your speedometer after putting different-sized tires on your car is beyond the scope of this writeup, and therefore will not be discussed except for this note: With a little math, it may be possible to use this writeup to get your speedometer a little closer, if not precise, depending on what tire size you've chosen.
How the speedometer works:
The speedometer (and odometer) are driven via a cable by a pinion gear in the rear of the transmission, right side. This gear meshes with the transmission's output shaft directly. The pinion gear can have anywhere from 16 to 23 teeth, depending on the differential you are using. All that is needed to make sure your speedometer is accurate, is to install a pinion gear that matches your differential (again, this is assuming you have the proper tire size). Pinion gears are also color-coded for easy identification. Here is a listing of available pinion gears, their colors, the differentials that they are meant to be used with, and their nissan part number. Important note: If you use a pinion with 20 or more teeth you must replace the sleeve that holds the pinion gear. The sleeves for 20+ tooth pinions are offset to allow for the larger size of the pinions. Not using the proper sleeve will destroy the pinion gear and possibly the drive gear inside your transmission.
|# Teeth||Color||Differential Ratio|| Part number
Click to order
By WindigoZ 04/01/03