anolis

I just got a '96 Ford Mustang GT Coupe, from a used car lot the other day. When I'm driving down the road the speedometer is WAY off from my actual speed. For instance when going 45 the speedometer reads 60, when going 80 it reads 100. I contacted my local ford service center about fixing it, they want to charge me in excess of 300 dollars. Can't the speedometer be reprogrammed via the OBD2 port?

The service tech I talked to said that because it was so off that gears in the speedometer unit would have to be swapped, I thought this was only applicable to mechanical speedometers.

So I come here seeking help of a more technical explanation of what to do, and how to do it for cheaper.

I have Nitto 450 tires, that are stamped with "P245/50R16"

powerfreak

the '96's have mechanical speedo's...They didn't change until '99. Check the rear end gear ratio...maybe it had a gear swap???

here's a link to re-calibration gears for your trans...
http://www.steeda.com/products/speed...tion_gears.php

anolis

how do i check my gear ratio?

powerfreak

you have to spin the rear tire around once and count the amount of times the driveshaft spins...so for example, if you had 3:73's...for every 1 time your tire spins, the driveshaft will turn around about 3-3/4 turns. If you have 4:10's it will go around a little more than 4 times.

sooooo, jack up the rear of the car (put on jackstands to be safe), put tranny in neutral. Use a piece of tape or something to mark the passenger side tire (and mark the same spot on the quarter-panel...so you can tell when the tire has gone around once). Spin the tire once and count how many times the drive shaft turns (you can mark the driveshaft as well to make it easier to keep track of).

cliffyk

If it reads 100 at 80 mph then you have 4.10 gears. You need the proper speedometer drive gear, or a SpeedCal.