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Q:

tranny wont shift on 1994 Ford Taurus

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
tranny wont shift when the speedometer isnt working
(4) Answers
(2) Comments
You gave me the clues needed to answer your question. The vehicle speed sensor is a direct input to your car’s computer that enables it to command to proper up shift. Garbage in= garbage out. Clearly, this is why your speedometer is inoperative also. The most common problem that I have experienced is the speed sensor is very close to the rear exhaust manifold and pipe. From the factory, a heat shield installed around to speed sensor is supposed to prevent melt down like an ice cream in July. Unfortunately, I have seen many mechanics leave this shield off causing sensor and usually the electrical connector to melt. It takes spider monkey hands and arms to access this sensor, but it can be down without removing the exhaust. I hope this helps.
As he stated, the electrical connector could be melted, and in need of replacement also. And as I mentioned below, you could also have a transmission driven gear issue.
Great answer from b-glaste.
Having been there before also, I want to caution you to inspect the driven gear in the transmission too. The VSS (Vehicle Speed Sensor) is common for failure for the reasons b-glaste mentioned, but I have seen a handful of driven gears in the AX4N / AX4S transaxle failed, causing the issues you describe.
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If you are having trouble with transmission shifting and speedometer not working at the same time. It will be pretty safe to say you have a bad input speed sensor. The speed sensor sends information to the speedometer and to the transmission control unit to shift at proper speeds.