This would probably be your best source for the info.
http://www.hanlonmotorsports.com/t5speedo.asp
It looks like if you have a 7 tooth drive gear on the output shaft, then a 21 tooth driven gear would be the closest.
http://www.hanlonmotorsports.com/t5speedo.asp
It looks like if you have a 7 tooth drive gear on the output shaft, then a 21 tooth driven gear would be the closest.
If removing and replacing the tailshaft housing to change the drive speedo gear isn't a good plan for you, here's an alternative:
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 within 1%-3%. The drawback is that it isn't cheap.
Please excuse the typo (their's, not mine) in the following picture - it should read Custom ratio adapters, not Custom radio adapters.
See http://www.gaugeguys.com/ratioadapt.htm for more info.
The stock range of speedo gears work correctly with a limited range of tire sizes.
See http://www.corral.net/tech/gearcalc.html for more help
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 within 1%-3%. The drawback is that it isn't cheap.
Please excuse the typo (their's, not mine) in the following picture - it should read Custom ratio adapters, not Custom radio adapters.
See http://www.gaugeguys.com/ratioadapt.htm for more info.
The stock range of speedo gears work correctly with a limited range of tire sizes.
See http://www.corral.net/tech/gearcalc.html for more help