Yeah, Andrew, that is probably what I will have to do! Can't think of any other options, other than bigger tires.

There is a cable of some sort connecting the speedometer back to the wheels. It could be the sensor or the cable or both. Since you started at the gauge, just keep working backwards until you solve the problem.Hope I helped!

Actually, I had posted a response to this but changed it when I realized that the poster is a spammer originating from India.

Edited March 8, 201016 yr by sblake01

I figured the same thing, Stephen, based upon the response ...

Having read this thread and having a problem with my speedometer off about 10%, (speedo shows 10% too slow) is it possible that my cable could be in a bind, causing the 10% difference? I did have a problem with a bouncing gauge but fixed it by bending the cable (the short one that comes out of the gauge and screws in right inside the firewall) and lubricating with cable lube. This is in a 1981 Turbo and automatic, 15" wheels, 205/60 tires.