Speedo calibration after gears

J_lope82 · Mar 19, 2023

I’m about to swap to 3.73 gears on my manual 96 GT. I thought I could calibrate my Speedo by changing tire size with Forscan. I tried it today and I’m not getting the option to rewrite anything on my PCM. I’m guessing because it was previously custom tuned.
Does any one know if I should be able to do it with Forscan?
What are my other options for calibrating the speedo on my car?
TIA

07GtS197 · Mar 19, 2023

You can’t change the speedo settings on the pre 99 mustangs. You’ll have to use something like an Abbot era or Dallas speedcal which are near impossible to find.

apsmith49921 · Mar 19, 2023

Dakota digital makes an adapter as well its only 100 bucks I've considered giving it a shot. Add power, ground and split the signal and should work

ttocs · Mar 19, 2023

use your phones gps for speed

J_lope82 · Mar 19, 2023

ttocs said:
use your phones gps for speed

Yeah I have that just trying to fix it right.

lwarrior1016 · Mar 19, 2023

Dakota digital gauge cluster will solve that issue.

J_lope82 · Mar 19, 2023

So a hand held tuner won’t work?

badass98svt · Mar 19, 2023

J_lope82 said:
So a hand held tuner won’t work?

Nope. Not with pre 99 Mustangs.

badass98svt · Mar 19, 2023

I've always used a Speedcal.

Frank.JD.Perez · Mar 19, 2023

Speedcal and i think you can also do that with a sct tuner. I have the speedcal on my car personally

lwarrior1016 · Mar 19, 2023

Tuners won’t fix pre 99. It’s not ecu controlled. It’s a signal straight off the speed sensor.

J_lope82 · Mar 19, 2023

I just saw that LMR has a calibrator for sale. The Abbott one.

badass98svt · Mar 20, 2023

Frank.JD.Perez said:
Speedcal and i think you can also do that with a sct tuner. I have the speedcal on my car personally

SCT will only work on 99+

Frank.JD.Perez · Mar 20, 2023

My sct gives me the option to on my 97 though

J_lope82 · Mar 20, 2023

Which SCT do you have?

lwarrior1016 · Mar 20, 2023

Frank.JD.Perez said:
My sct gives me the option to on my 97 though

It will give the option, but it doesn’t work. The speedometer is a signal straight from the sensor.

Maximum95 · Mar 20, 2023

Are '96+ cars not like T5 cars? You can't change the speedometer gear? Or is '96+ stuff all digital signal...

cobrajeff96 · Mar 20, 2023

You can change the speedo gear inside the trans. It'll get you close. Not perfect, but just about. For my application, I would up using a red (21 tooth) and it's been great. Granted, a lot has changed because of T-56 Magnum, 4.10 gears, different tire sizes since OEM form, etc.

The mid/late 90s Mustangs are electro-mechanical so you have options. The Dakota Digital SGI-100BT is another great option and one I currently use and I can't recommend it enough. It'll do both speedo and tach. But the real icing on that cake is the bluetooth smartphone app interface. You can literally watch your speedo needle change as you drive and tweak the settings on the app. So cool.

Files attached.

whiplash473 · Mar 20, 2023

I changed the worm gear in my T-5 (purchased from LMR) and it got it close, as cobrajeff ^ said. It isn't exact but it's within one or two miles per hour.