That is a nice calculator, yellowgrabber, but it only has an option for a C6 automatic. Do you know if the calculations would be the same for a C4 automatic?
I don't see how that guy came up with the notion that C-6's have a removeable drive gear, all the Ford automatics have the gear cut into the output shaft. And he's off on the asssumption that Toploader speedo gears all are cut the same direction, the Galaxie Toploaders have the speedo gear going in the same side as the automatics and the gears for these are like the automaitcs in that regard.
I've been looking... I had another one bookmarked on my PC at home but I'm on a business trip right now. I believe it had C4 and common overdrive transmissions. I'll keep looking, but I have to believe the calculations (i.e., # of teeth for the transmission and speedo cable gears for specific tire height & gear ratio) will be the same. I know for sure that Toploader manual has a removable colored gear but I think we have concluded that the Automatics do not have a removeable main shaft/tail shaft gear so you would really be stuck with selecting the closest gear that goes on the speedo cable... like with the C6. Make sense?
