So I just bought a 67 mustang and the guy I bought it from does not know what it has for rear end gearing. I believe the stock rear end was setup with 2.73. It is a 289 C code 67 stang coupe that originally had a 3 speed. It now has a 4 speed top loader in it. 65mph = about 3000RPM in 4th gear with 235/60/14 tires. I thought I could just jack one rear wheel up (open rear end) and spin the tire while counting the drive shaft turns vs the tire rotations. What I came up with was 102 rotations of the driveshaft per 60 rotations of the tire. This gives a ratio of about 1.7 which cannot be right. What am i doing wrong, or does this method not even work?

Thanks

 

You should be able to spin the tire around once and see how many turns the driveshaft makes. For example, a 2.73:1 will spin the driveshaft 2.73 revolutions per one revolution of the tire.

 

Try this it is in the FAQ http://www.csgnetwork.com/gearratcalc.html