I drove my 87 Shelby Z from home to the LA auto show this weekend, it's about 60 miles according to gps. The odometer really hasn't ever worked since I have owned this car, which doesn't really bother me. I looked down shortly after starting my drive to see the odometer working, but at a fantastic pace, the miles were adding up much faster than normal. The car counted over 300 miles on a 60 mile drive. Crossing a fwy bridge which is a few hundred feet long added up to 3-4 tenths of a mile. Speedometer was reading normal. The odometer turned fast regardless of speed, and only stopped when the car stopped.

Now I am not concerned about it that much, but more curious as to what would cause this? And it stopped working when I left to drive home.

Thanks