I have an 81 300 TD Wagon with a 4 speed manual (stock? I don't know). My speedo is pretty accurate up to about 30 mph. Then, like Zerohour3K, it gets exponentially worse - reading slower than I'm actually going. When I checked the speedo against the mile markers, it showed 9/10 of a mile for every actual mile travelled. I guess this means the car has more actual miles than the odometer shows. What can we do to correct this?