I recently had the car to repair shops and they replaced a sensor over the rear axle, another mechanic checked a device in the transmission and said it was OK. What else could cause the speedometer to work intermittently?
Speedometer works sometimes, and sometimes stops working on 1994 Buick Roadmaster
There could be a corroded wiring connection, for instance. Also could be the dash gauge failing. Sounds like you need some help, here's a directory link for you: