ConcoursMustang Forums
Restoring - General discussions that span across many different groups of years and models => Drivetrain => Topic started by: truetriplex on July 19, 2020, 08:53:20 AM
-
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?
-
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?
-
What model year, engine and transmission? Info in MPC. Perhaps shop manual also
-
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
-
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.
-
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.