How do you repair the speedometer on a 1999 Ford Escort?
Replace the VSS and wires.
This is very common on the 1996 Ford Escort unfortunately. Basically the speedometer cable has to be re-greased or the speedometer has to be replaced with the older 80mph model. Both "fixes" require disassembly of the dash to get to the cable/speedometer. See the ford escort owners association for more details/instructions.