Speedo calibration after gears

J_lope82

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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
 

apsmith49921

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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
 

cobrajeff96

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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.
 

Attachments

  • Speed Dial specific instructions.pdf
    1,011.9 KB · Views: 5
  • Transmission Speedo Gear Chart.JPG
    Transmission Speedo Gear Chart.JPG
    64.1 KB · Views: 8

whiplash473

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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.
 

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