Speedo jumps around above 40 mph.

Hi,

I have a VFR 800 Fi with a malfunctioning speedometer and would appreciate some advice on how to fix it.

The speedo is OK up to about 40 mph then it starts to bounce about erratically, when I get above 40 mph.

I have already replaced the nylon nut that connects the speed sensor to the sprocket bolt. The battery and charging system are fine.  I have also determined that the correct voltages are present at the speedo sensor and at the instrument cluster. There is continuity in the pink wire running from speedo cluster to the speedo sensor, and I am getting a fluctuating voltage (between 0 and 4.8V) between the pink and green/black terminals at the back of the instrument cluster when spinning the back wheel.

Following the advice in the Haynes manual it suggests that the fault may lie in the ‘speedometer or the instrument cluster printed circuit board’.

Has anyone else had a jumpy/erratic speedo that was due to defects in the speedo or PCB?

Given this is speed related, I would still think the coupler at the sprocket bolt would be a likely cause. Are you confident the coupler is making good contact onto the bolt, it is easy to damage the coupler if you refit the speed sensor without aligning the coupler on the bolt first.