Speedometer re-adjustment

My speedometer needle recently broke off due to dry rot, but after I installed a new needle the reading was all off. It would say I am going 55mph when I am actually going 45mph. And when I accelerate hard the needle jumps up too quickly. Can anyone tell me how to adjust it back to it's correct setting? thanks!

 

Good luck.

The speedometer needle in a Yamaha mechanical speedometer forms the "back stop" for the spring; the amount of pre-load on the clockspring when it's at rest determines the tension of the spring throughout its range.

When you remove a speedometer needle, it's important to mark its original relationship to the magnetic drum so that when you re-install or replace the needle, you maintain the same preload on the clockspring.

If you didn't "index" the needle to the mechanism and mark it, before you disassembled it, you've broken a precision adjustment and the only thing you can do now is "trial and error" repositioning to increase the preload ever so slightly. Increase it too much and it will read slow instead.

Sorry.

Yamaha mechanical instrument tech: http://xjbikes.com/Forums/viewtopic/t=15303.html

 

thanks bigfitz!