Speedometer off by 4-5MPH

[Kenneth]

Hey guys, I have been dealing with my speedometer being off by 4-5 MPH and I had my tires/wheels and gears changed a month ago. 16"-->17" and 3.27---> 3.73 The mechanic that tuned it for me said it is okay to run it like that but it irritates me. I have a GPS I use and that tells me approx. that I am about 4-5 MPH off. I dont know how to use the Ford Racing Pro Cal tool. Would anyone care to teach me sometime? would be great if we could even fix it all together. :(

[Nicoleb3x3]

um.....what year stang? I'm not sure if the pro cal tool you have is for a newer stang (with the obdII computers) which just need the computer to be told about the new gear ratio using that tool.

however....if you have a 93 and older with a mechanical speedometer, then you need a speedo gear that you swap at the end of the speedometer cable down by the transmission.
http://www.latemodelrestoration.com/Product/Search?q=speedo%20gear

There's a situation on 90-93 air bag year fox body, I beleive just on automatic cars... where you actually max the speedo gears available (like me!)
The fix for it is to send out your speedometer to someone who can do custom mechanical speedometer rebuilds (if you have that situation let me know and i'll look up a guy I know who can do it) I have a guy doing my saleen 200 mph speedometer and he's also going to work on getting those last few 5mph issues I have worked out (I also run 3.73 gears)

....so again, if you have a newer stang then that tool you have should make it easy, plug and play and scroll through the menu (if it's similar to the sct tuners)

[LILBLKSNAKE]

I have the Dallas Mustang Speedcal on my 97 COBRA, it wires into the tranny and has about 20 switches that you set based on your mods. Speedo is pretty close with 4.30's and new 18" chrome FR500's

[ToplessPony94]

If you need a Speedcal, I have a brand new one hanging around and will give you a good price on it. Just PM me. I just never get around to posting it up for sale.

[Kenneth]

The car is a 2006 and the Ford Racing Pro cal is M-12655-D, other than that there is no other marking on here to say what version the pro cal is.I believe I will need a speed cal that you speak of. will it account for my gear change and my wheel change? I am a little lost here but I do know that my car is saying it is going 4-5 mph faster than it really is. I am putting extra miles on it that it isnt going so id like to fix that ASAP! Is this speed cal good enough? http://www.americanmuscle.com/ford-speedo-tool-9410.html. also if this can be fixed with my pro cal does anyone know how to do it and if they have some time like maybe at the next cruise night would be fine if anyone wants to help. I am kinda done paying $50 an hr to people who dont know mustangs that well.

[ToplessPony94]

The one I have is different, but like that one it has many settings. I expect it would do the job. As for the pro-cal, I don't know much about that so I won't try to advise you there. If that can work, it would be the most cost effective solution, since you already own it.

FWIW, most people mount speed-cals under the console, not under the hood as American Muscle shows where weather can get to them.