Changing to 3.73 gear on a Bullitt

[tomsgarage]

I know this is a SVT forum, but my son has an 01 Bullitt Mustang that we have just changed the rear axle gear to a 3.73. (He figures he will get my 03 Cobra one of these days, Ha ha) What we need help on is speedometer calibration. We tried to change the gem module at the Ford dealership I work at but it would not accept the 3.73 ratio. Looking for advice on what to do. Thanks :huh:

[Steve Bassen]

Try one of these:

http://www.abbott-tach.com/era.htm