Gear Ratio of a Drive Unit

To figure the overall gear ratio of a drive unit you must do the following:

Gearcase: Count the number of teeth on the drive gear or
          pinion gear and the number of teeth on the driven
          gears forward and reverse. Then divide the drive
          gear tooth count into the driven gear tooth count.

Sample:
pinion gear = 17 teeth

forward / reverse = 28 teeth
   
       28 ÷ 17 = 1.6470588 ( round to, 1.65 )


Drive shaft housing: Count the number of teeth on the drive gear
                     or "U"-Joint pinion gear and the number of
                     teeth on the driven gear. Then divide the
                     drive gear tooth count into the driven gear
                      tooth count.

Sample:
"U"-Joint Gear =   20

upper drive
   shaft gear  =   24

      24 ÷ 20 = 1.20

Now multiply the 1.65 times the 1.2 to find the overall ratio answer.

Sample:

                1.65
               x1.20
              -------
               3.30
              16.50
             --------
              1.980  =   (1.98 over all ratio )