Speedometer gear size

[Ralph]

What speedometer gear would i use for my 73 cuda ?

355 rear axle ratio with tires P235 / 60 R15 which is 26.1 high

I was thinking Red 36 teeth

What do you think ?

Thanks to all
R

 

[moparleo]

MyMopar - Mopar Forums & Information - Speedometer Gear Selection Guide

 

[Ralph]

Thanks Moparleo

 

[340challconvert]

Hope this helps!
Your tire 235-60R15 w 7.4 diameter 26.1

Gear Part # color Tire Diameter

3.55 2538939 (Green) 24"

2538936 (Red) 26"

2538933 (Yellow) 28"

2538931 (Green) 30"

Please Note: These part numbers are for the standard style pinion gear. The last two numbers of the part number is the number of teeth for the gear (Example 2538943 = 43 teeth).

Here is an example on how to calculate the wheel diameter to select a speedometer gear to use with the desired ring/pinion gear.

Example
Tire Size: 245/60/15

245mm/25.4mm = 9.64 Inches Section Width

9.64 in. X 60% = 5.79 in. Side Wall Thickness

5.79 in. X 2 = 11.57 in. Total Side wall height

11.57 in. + 15 in. (Rim Size) = 26.6 in. Diameter

So with this Tire Size and 3.91 Gears, I would use a 40 Tooth Speedometer gear.

Looks like your calculation for the red gear as correct

 

[Ralph]

Hey thanks for the confirmation !

 

[Ralph]

When I replace the speedometer gear will I lose alot of trany fluid or is it high enough not to plan for it. Is it easy to change ?

 

[Mopars & Missiles]

When I replace the speedometer gear will I lose alot of trany fluid or is it high enough not to plan for it. Is it easy to change ?

Put the back end up on jack stands (or higher than the front) to help keep the fluid up front. You won't loose much at all this way. Real easy to change the gear, pop out the old one and insert the new. Keep in mind to check and make sure the adapter is indexed correctly for your new gear before you close it back up.

 

[Ralph]

Thanks much !