1998 Ford Taurus problem with speedometer

Hey guys and gals,

I have a 1998 Ford Taurus FFV with roughly 256,000 miles.

My problem is that I am having problems with the speedometer. Lately, it has gotten to the point that it is getting stuck at around 42 MPH.

What I mean is that I can be sitting perfectly still at times, and then I look down and it says that I am running 42 MPH, RPM's do not change at all. Then when I stop and turn off the car, it goes down REALLY slow, then when it does want to start working again, it is almost like a magnet lets it go or something and the needle just drops and then it starts working again, and then it will work fine again for a while. Also, when it is not working, I can pull over to the side of the road and it will slowly start going down, the lowest it will go is around 20 MPH, then the other odd thing is that if I go to take off again, the mileage shoots right back up to 42 MPH, even if I just inch up a few feet and stop again. This is periodic. I pulled the cluster out and saw that all there is is two electrical connectors at the top, so there isnt like a gear or anything for the speedo that I could try to grease or anything.

This problem is driving me absolutely crazy. I am in school for automotive mechanics, so I am still learning. I need some help or some suggestions. I drive this car 120 miles a day, so I need to find out how to get it fixed, if it is simple, do I need to replace the whole instrument cluster, etc.

Any help would be greatly appreciated.

Thanks so much.