Transmission ate my gear...

What year car and what transmission and rear axle gear combo are you running? No teeth on the gear or no gear on the end of the speedo adapter/VSS sensor?

If it is a T5, what is the tag number on the rear casing of the transmission? T5's had 7 or 8 tooth speedo gears on the output shaft, and the simplest way to tell is by the tag number on the rear transmission casing

You post does not have enough information to give you useful answers.

The 23 tooth white gear works good for some guys, but self destructs in a few months for others. There is no cheap fix if the gear chews up quickly.

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 Speed Correction Devices (Ratio Adapters) for more info.