[alexs0628]

Have a Mercury Tracer Trio 4-speed automatic trans. It has trouble shifting into 4th. If I drive in D, I don't have a problem, since the car then nevers shifts into 4th gear. It does shift into overdrive, but it's rough, and shutters. Is there a sensor, or switch that controls the shifting that could be bad? This car is just an around town vehicle and rarely is driven over 45 mph. Can I just drive in D and not in overdrive? I don't want to put much money into such an old car.