YOu need a new speedo gear in the transmission. Go the the D&D preformance website. They have a chart that tells you which ear you need. Your local Ford dealer will have the gear for $15 or so.

 

To get you close you will need a 23 tooth gear, this will get you close, app 5% off. To get it exactly, you will need to change out the internal drive gear from 8 to a 7. After you change that to a 7, you can use a 21 tooth. The 23 tooth gear will get eaten up with the stock 8 tooth gear after a while.

 

so what youre saying is get a 7 tooth internal gear and a 21 tooth?

whats involved in switching these out? i know the first one is pretty easy, what about the internal gear?

 

Hanlonmotorsports.com has a calculator that will tell everything you need to know. They also sell all the gears. That's where I bought mine and it was 100% acurate. Not off by 5%.

 

There was a post on here a couple of days ago saying that speedcal will work on our cars. I'd look into that, as it's easier and more accurate than changing the gears. The speedo gear is easy to change, but to change the drive gear you're talking about dropping the driveshaft and taking the tailhousing off of the tranny, i.e. taking the transmission apart.

 

I used the 23 tooth speedo only and am within 1 mph off.

 

I used the 23 tooth speedo only and am within 1 mph off.

Yes, but it's not linear, meaning the faster you go, the more you're off. At 30 MPH it's spot on. At 100, it's about 5 mph off. It all depends on how accurate you need it to be.

 

If it were my speedo, I would want it to be dead nuts all the time...

 

If it were my speedo, I would want it to be dead nuts all the time...

Truth.

what is this 'speedcal'?

 

DMP's SpeedCal Corrects Speedometer readings on 1996 and up Mustangs when the rear end gear or tire size has been changed. A great fix with quick, simple installation on all 1994 and up 5 speed equipped Mustangs and 1994-98 automatic equipped Mustangs. When ordering, if you give us your tire size, stock and current rear end gear, stock and current speedo gear tooth count (if it has been changed from stock), we will pre-set the SpeedCal for you. You can also use our 'SpeedCal Calculator' and do your own calculations.

Sounds kind of misleading with the "1996 and up" and then the "1994 and up", but supposedly it works on our cars. Worth checking into, although it seems to be a pain to install.

http://www.dallasmustang.com/index.mvc?Session_ID=3E9D702300063C8900004A9A00000000&s=speedcal

 

It's not a paint to install, but its a hit or miss on whether it works right or not. However, if it's one of those that doesnt work right, they will replace it for free.

 

Can it be adjusted through a chip or the Tweecer???

 

Can it be adjusted through a chip or the Tweecer???

Negative. It's not computer controlled (on our cars). I'm sure the computer is aware of it (maybe), but it's not modifiable. My best guess is that the speedcal hooks up between the transmission and speedo and modifies the signal coming from the transmission that tells the speedo what speed to display. Either way it's hard wired in.