So I have been searching for a driven gear for the 3 speed i have in my 1951 truck that is not original. it is a GM 3 speed. Case number GM15, 3354726, E245. The tailpiece is GM8, 8866722, E226. The P.O. converted it to a floor shift. The hole for the speedometer gear housing does not have threads. The housing has an O ring and is missing the driven gear. I looked into the hole and the drive gear looks good. What is the correct driven gear for this mystery? I understand to have the speedometer read correctly, you calculate the tooth number of the driven gear based on tire size ( 235/75 x 15), rear end gearing (3.90) and revolutions/mile. The formula I was given was driven gear=drive gear x rear end ratio x rev/mile divided by 1000. With my tires and rear endangering drive gear tooth number ( estimated by looking into the hole), I came up with either 14 or 16 tooth driven gear. I don’t know if this is correct but it is a start. My first concern is to locat a correct driven gear. Thanks for this site- it has helped immensly in my gentle restoration of my 1951 5 window 1/2 ton. Hopefully it will be rolling before the snow flies.
