I have a 2002 Ford Windstar Sport and the speedometer only records speeds up to 30 MPH no matter how fast I drive. Is there a transmission or wheel sensor that needs replacing?

its connected to the transmission - check connections top and bottom.

The speedometer cable is connected to the transmission, usually with a little clamp with a small screw through it. Clean the cable, the clamp and the area around where it goes into the transmission. Loosen the clamp and pull out the cable. There should be a small plastic gear on the end of the cable or up inside the hole it came out of. Clean off the gear and check in for wear. They will wear out sometimes but you can get a replacement from some parts places or the Dealership. Be sure to get the same cooler gear with the same number of teeth as the old one. Put a little grease on it and reinstall. Also, look at the end of the cable where the gear goes on it, it should be nice and square so the gear turns it and does't slip around and around on it. This would be my first guess to fix your problem. If this isn't the problem see if you can get to the back of the speedometer and check the cable connection or the wear on the end of the cable. If that is all OK then you may have to pull the speedometer itself out. If you do pull it out, look for anything that looks bent or jammed in where it doesn't belong. Usually a magnet on the end of the cable spins close to a metal plate the needle is hooked to makeing the plate turn against a spring of some sort. All this stuff has to be clean and not bent out of place or anything. It usually takes a qualified repairman with the right equipment to fix a speedometer right if it has been messed up somehow.

pROBLEM MIGHT ALSO BE IN THE DASH IF everthing else appears well