Speedometer gears- 1940's 4 speed truck transmissions

[fordblitz]

Hello,

While working out my speedometer cable for my 1943 Ford Canada CMP truck I was looking at speedometer gears and found that the 4 x 4 transfer case speedo driven gear is unique to these vehicles and not a standard Ford item.

Just for curiosity I looked at what the standard Ford car and truck gears were and found a list of what was used in the Forties for various tyre and diff combos.

For 4 speed truck transmissions:
An example is 19 tooth driven can be used with 6 or 8 tooth drive gears.
Also 20 tooth driven gears can also be used with 6 or 8 tooth drive gears.

The question I am asking is how can different tooth number speedo driven gears be used on the same tooth size drive gear? The geometry of it doesn't seem possible. I know later GM cars used an eccentric driven gear housing to be able to rotate it to get proper engagement with the drive gear using different size gears. Did Ford do the same?

Found the link on here Ford Barn:
http://i1059.photobucket.com/albums/...rGearChart.jpg

Attached is a commercial 20 tooth gear from a 4 x 2 Ford army truck, and the 15 tooth transfer case speedo gear.

Will be interested to find how it is done as I don't have any commercial 4 speed truck transmissions to view. Thanks.

Cheers