Speedo Woes - Electronic Speedo Erratic

[rotorwings]

While out for a drive today I noticed the speedo needle bouncing around very erratically. It would sometimes appear to be fine, and then, once getting up to a certain speed, the needle would bounce around all over the place (between 0 and 100+kph). Later in the day it seemed to work up to 70kph fine, then bounce around after that. Still later in the day and it just seemed to bounce around under any circumstances or speed.

I have checked the grounding of the connector to the speedo and there is basically no measurable resistance between the connector and battery. There is also about only .9mm between the sensor and the toothed ring on the rear axle. I checked and reseated the connection to the sensor, but this had no effect.

What are the likely causes?

[rotorwings]

Anybody? There must be someone who has seen this and fixed it.

[rotorwings]

sjmmarsh said:

....it sounds like you have the newer type driven by a Hall effect switch mounted on the rear right hub?

You are on the right lines that it is probably an earthing issue - what happens when you turn your indicators on - no effect, or does it bounce in time with the flashing? Does the indicated speed drop rapidly when you apply the brakes gently?

Yes, it's an electronic speedo with a hall effect sensor.

I had read elsewhere about the possible electrical issues, but indicators, lights, etc. appear to have no effect.
Braking also appears to have no effect.

Sometimes the speedo will progress without a problem up to about 60kmh, then drop to zero and/or bounce around.

[rotorwings]

DCL said:

Typically it's the cable that flexes and breaks internally. Easiest solution is to replace the sensor, but if you're good at soldering then you can replace the wire. I replaced mine with microphone 'superflex' cable that has a much longer life.

I'm quite handy with a soldering iron, so I'll check this out. Are you saying that the problem is likely in the cable from the sensor to the first connector (which is usually cable-tied to the chassis near the rear axle)?

[rotorwings]

Well, I couldn't find any problem with the wires or connector. The LED was responding as expected and there seemed to be a stable 5v across the signal and earth (-ive) wire no matter how I wiggled the wires.

So remounted it, but this time I gave it more clearance to the teeth (about 2mm, instead of 1mm). Now, everything seems to be working fine.

I'm not sure why, after 3 years, this should now make a difference though.

One last possibility is that it might be temperature related as it was quite warm when it was playing. I guess I won't know 'till next year now.