changing turtle speedometer drive question

M

Matt in Alameda

Senior Member
In my 1935 Ford 5 Window coupe, I have a 4.11 rear end ratio. The speedometer turtle on the torque tube is stamped with the number 19...this is for a 3.78 rear end and explains why the speedometer is inaccurate.I am looking for a turtle with a 21 to go with the 4.11 rear end ratio. My question is, do I have to also change the gear that is driving the turtle that is on the drive shaft?........Thank-you,.....Matt in Alameda
 
No - the same shaft gear is used by both. Only the gear in the turtle is different.
 
The actual assemble part number would depend on the tire size. The Green Book list the combinations, such as:
A-17270-E 21 teeth for 4.50 x 21 tire
B-17270-B 21 teeth for 4.75 x 19 & 5.25 x 18 tire
and so on.
 
I thought you were asking about the driving gear, not the speedometer drive gear. If so, per the Green Book middle of Page 632: "The B17285 Driving Gear (7 teeth) is used exclusively."
 
Thank-you guys..DD931 was able to decipher my garbled post best. This site is fantastic, I would have never attempted this project if it didn't exist...... a very, very sincere thanks to all of the contributors.....Matt in Alameda
 
Hey Matt...if you have a difficult time finding the entire turtle, you can just change the gear inside. That is what I did. PM me if you want to know the details.
 
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