I now own a 94 5.0 that has 3.90 gears in it. The person I bought it from never had the speedo calibrated. I know there are a couple of ways to get this corrected but need some details/hlep. Any help is appreciated. Thanks

Well as for the speedometer itself I'm not sure how you could get it calibrated. I'm sure there are probably specialty places that could calibrate a speedo but I dont know of any.

The only way I know of getting the speedo to read right is by changing the speedo gear that is at the end of the speedometer cable bolted to the transmission.

You might find this post helpful...
https://www.muscularmustangs.com/forums/ ... .php?t=739

I have read and seen all of that but my problem is the 3.90 gearing is not on the chart. This seems to be a non existant part. Everything I have read or seen goes from 3.73 to 4.10. Just skips right over 3.90. Anyone...please....I don't even like driving the car not knowing how fast I am going. Cannot afford a ticket right now. Thanks for the help.

http://www.hanlonmotorsports.com/t5speedo.asp
There isn't really a "match" for your set up. Depending on tire size, this is prolly as close as you can get. As far as a speeding ticket, your speedo currently reads slower than your actually going. the faster you go, the more it is off.

LOL, I don't know what I was thinking but when I first read your post I thought it said 3.08 gears.

Have you tried going to your local Ford dealer and seeing if they can get you a 22 tooth speedo gear? The 21 tooth gear works great with 3.73's and the 23 works with 4.10's so I'd assume a 22 tooth gear would get you pretty close. To be honest I don't know if they even make a 22 tooth gear but since they make a a 19, 20, 21, and 23 I'd assume they also make a 22. If your local dealer can't help you they try contacting Ford Racing directly as I'm sure they'll be able to help you out.

As for why you don't see people mentioning 3.90's that is mostly due to 3.73's and 4.10's being so popular.

Im running 4.10s in the rear of my 94gt and had the correct speedo gear installed but the speedometer is still off by about 10 miles. I would just get the closest one to your setup, grab a couple cell phones and follow someone in a newer stock car at about 55mph and see where your at. Once you get the difference figured out youll get used to it.

Its actually about 15-20 miles faster than what I am going,.,not slower. I will try and find a 22 tooth gear. Thanks for all the help everyone.

The 21 tooth gear is actually for the 3:27 ratio.

You want a 23 tooth gear to get close. Actually, a 24 tooth gear is probably extremely close to what you would need. (the 23 tooth gear is white)