[Wifes66]

I have a C4 automatic transmission, 2.8:1 rear axel ratio and my tires will be P225-60-15's.

Any idea which speedo gears (drive and driven) that I need to use?

Steve

[Montana's Stang]

Steve,

I don't believe you can change the drive gear (the gear inside the transmission) without tearing down the tranny, but I could be mistaken (I have a 4 speed and I can't change mine from outside the tranny).

CJ Pony Parts has a chart in their catalog that will tell you which driven gear (end of cable) that you need based on your model year, engine size, transmission, tire size, and rear end ratio.

They also provide this formula:

(# of Drive gear teeth) X (axle ratio) X (tire revolutions/mile)
---------------------------------------------------------- = # of teeth on the driven gear
1000

They say to go to the nearest whole number of teeth to the answer from the above formula (if you get 21.3 from the above, order a 21 tooth gear). I don't know how you find out how many teeth are on your drive gear. Maybe someone else on here knows.

I could not find the chart or formula on their web site (CJ Pony Parts - Ford Mustang Parts) but you can order a free catalog from their site.