Wont Shift and Speedometer Quits Working

Our car has about 111,000 miles on it. While we do not drive it all the time it has always been reliable and it is good to have around for a backup or driving in winter weather.

Recently, it has developed a problem where the speedometer will quit working and the transmission wont shift out of low gear. This only seems to happen after the car has been driven for ten miles or so and everything has gotten up to operating temperature. If you let the car set for a few hours and cool off the speedometer will work fine and the transmission will shift. That is until the car warms up again and everything starts over.

I have replaced both the vehicle speed sensor and the speedometer driven gear (which drives both the sensor and the speedometer) but nothing has changed. At this point the only thing left to change would be the speedometer drive gear on the output shaft of the transmission. At least that is what I think.

The part that seems strange is that everything works fine until the car warms up. I keep thinking that if the speedometer drive gear is truly worn out if should not work at any time instead of just quitting working when the car has gone a few miles.

Any information or ideas will be greatly appreciated.

Thanks.