by John Hart » Sun Dec 31, 2006 1:43 pm
Shaun... I had a speedometer that didn't work, and decided to very carefully dismantle it, to see if I could see the problem. It was fairly uncomplicated, but delicate inside. The main mechanism, was a flat coil that unrolled as the pressure increased.... As one person blew hard into the inlet tube, you could see the coil move.... It worked like the party things that extend as you blow on the mouthpiece.
In my case, the coil was working fine, but the speedo faceplate (flat black circle with markings and labels) was so distorted, the needle was not able to move... We carefully heated this plate and made it flat again... then the neededl could move and register properly...