Topic: A/T transmission speedometer gear

[truetriplex]

My rear axle was converted from a 3:00 to a 3:50. With the stock tires, what tooth/color gear should I put in the transmission to obtain correct speedometer reading?

[RoyceP]

Depends on whether you just want what Ford did or if you want accuracy. Are you using sized stock tires? Or something else?

To illustrate what works, I have 3.50 gears and F70-14 Firestone bias ply tires on my green GTE and the speedo is accurate. It has the black 20 tooth gear installed.

My rear axle was converted from a 3:00 to a 3:50. With the stock tires, what tooth/color gear should I put in the transmission to obtain correct speedometer reading?

[67gta289]

What model year, engine and transmission?  Info in MPC.  Perhaps shop manual also

[1967FEGT]

Because you likely can't get or won't the exact tire diameter used by Ford here's a simple calculator to determine your required driven gear.
https://www.moveras.com/Support/Tools/SpeedometerDriveGearCalculator.aspx

[Coralsnake]

Ford used the #CODD-B part number CODD-17271-B / GOLD colored /18 tooth speedogear on a 428 CJ/ auto with 3.00 gears. As you stated you still have the E70x15 tires

That information comes directly from a factory build sheet.

[Coralsnake]

That changed to a # C4OA-A part number C4OZ-17271-A / Red / 21 tooth gear with a 3.50 axle, again from factory paperwork.

That would be a good place to start.