Quote:
Originally Posted by Clrascoe
I think I need to replace the speedometer driven gear on my 47 Ford Coupe. Does anyone know if that can be done without dropping the drive shaft. I don’t see a way to get to it.
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I assume by "driven gear" you mean the one in the turtle near the front of the torque tube. Even though it is in a blind spot from the underside, the turtle can be easily removed from underneath. First unscrew the knurled nut that holds the speedometer cable to the turtle, pull the cable out of the turtle and move it aside.
With a short 7/16 box end wrench you can feel and unscrew the two short bolts that hold the turtle to the drive shaft. There is a thin gasket so you might need to tap the turtle to get it unstuck from the gasket.
The turtle may have a number cast onto it, probably 18, or 19, depending on what rear end gear ratio the car was delivered with. That number corresponds to the number of teeth on the driven gear in the turtle. I think the 19 tooth goes with 3.78 rear ratio and 18 tooth for cars with 3.54 rear end gears. The turtle housings are ever so slightly different because the number of teeth affects the gear diameter, the 18 tooth being slightly smaller diameter than the 19 tooth. But I am guessing you could use a 18 tooth gear in 19 turtle with no change. To put a 19 tooth in an 18 housing, maybe use two or three gaskets.
How do I know all of this? I switched from 3.78 to 3.25 rear end gears and needed to go to a 17 tooth speedometer gear, as used on some Model A cars. I had a 19 turtle and with the smaller diameter 17 gear, the teeth did not fully engage, causing erratic speedometer. I was able to file down the 19 turtle enough to get the 17 tooth gear to engage.