American muscle car guy

Hello everyone,

I'm sure this question has been asked somewhere on this site, I'm just having troubler finding the answer so here's my question.

I have an '87 GT with a T-5 that is in the shop being rebuilt. I converted from the 85mph speedometer to a 140 unit. My car has the stock gearing (just a little over 2.7 revolutions of the propeller shaft for one revolution of the axel; 2.73 or 2.76?). The tire diameter with my 16 in pony wheels is ~25.5 in., so what would be the correct speedometer gear for this combination. I know each gear is color coded diffrently and they can be plused up or down depending on the tire diameter. Also since the transmission is apart, should the plastic gear on the main shaft also be changed (its yellow in color) or is this one just generic for all the possible combiniations? Thanks for the correct input (no pun intended) and I'll be taking the information to my Ford dealer in order to get the correct part as soon as I get the difinitive answer.

Tony71502

http://www.latemodelrestoration.com/...lication-Guide

Best check your rear end gears first. Unless you know this rear came from an automatic car.

Tire size will have an affect on the speed displayed, but not that much.