My original speedo/odo died on me awhile back. Through the generoisty of a member here I acquired an entire instrument cluster.
It's pretty easy to get the dash apart. The service manual details the procedure.
Because I had another instrument cluster I wasn't too concerned about destroying the old one and I did taking it apart!
(All the pics are of the old speedo. BTW The original unit's gears were a bit chewed up and it clicked when the cable turned but the needle didn't move)
This is the face on view. The small shaft in the middle drives the needle.
I was planning on resetting the new odo to my original's mileage (a difference of about 30K miles). Problem was I couldn't get the unit apart. All the assemblies are staked into place preventing tampering, er... adjusting!
So admitting defeat I endeavored to understand how the unit worked. The cable turns the white worm gear. The odo is gear driven through the series of gears.
Pretty straight foward but the speedo hmm how the heck does that work. There is a magnetic disk directly attached to the white worm gear. The cable spins the disk. The disk sits inside an alluminum cup but doesn't touch the cup. The cup is attached to a shaft that turns the speedo needle. There is weird looking spring attached to the same shaft. WTH?
Googled: It's an "eddy current speedo" basically the spinning magnet creates electric currents that move in the direction of rotation which cause the "speed cup" to turn. The "hair spring" provides resitance to the cup and returns the needle to zero.
Here's a page that explains: How do speedometers work
I'm guessing that the magnetic strength of the disk varies (from unit to unit) so that would explain the speedo error and the differences between bikes. My original unit was 10% optomistic.
One more thing the trip reset. It's gear driven but it's spring loaded to reset to zero when the gears are disengaged:
The new cluster is installed and it gave me a chance to clean up my wiring mods (heated grips, GPS, conspicuity lights). I originally used the crimp on wire splice deals and they were getting flakey. Lesson learned I soldered and shrink wrapped the splices.