i was wondering if like a transmission shop would be able to do that. i would be getting the 140mph and i have 3.73 gears. i dont really want to send it into someone if i dont have to.
are there two speedo gears? one behind the gauge and one from the tranny?
"Speedometer gears:
An important consideration during the gear swap is finding the right drive/driven speedometer gears per your application. Ford used a seven (7) tooth drive gear in the 1983 to 1989 T-5's, then switched to an eight (8) tooth drive in 1990 (which would be 140mph..i think) (used through 1995). If you have 3.73's with an eight-tooth drive, and the highest driven gear with twenty-three (23) teeth, the speedometer still reads 5% fast. (5% is close enough) .
Check this link for more info on the proper gearing. By removing the speedo cable and peering into the tranny with a flash light you can see the color drive gear you have - that will tell you how many teeth are on it - if it's a manual. If it's an auto, the gear is integral to the tranny. However, if you're changing the speedo too, the easiest thing would be to get a reduction box from one of the speedo companies. It will plug into the tranny, and the speedo cable will plug into it - you will then have the ability to change gears in the reduction box to match up car speed to speedometer. Do a google search under 'speedometer' - and you'll get a bunch of hits on shops that can help you make the 140 speedo read accurately.
Here's more info on the gearbox Michael was talking about...
Check to see if there is a speedometer shop in your area. If there is, ask about the Stewart-Warner speedometer gearbox. I believe it is either a 777 Series Drive Joint Kits and Parts or 666 Series Drive Joint Kits and Parts. It is a small gear box that fits between the speedo pickup gear on the transmission and the speedometer. It has quick change gears that allow you to choose almost any tire size and rear end gear ratio you want. This will allow you to get the accuracy with within 2%-3% or less. The drawback is that it isn't cheap.