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Well after 18 months off the road my Falco is finally road legal with a new (ish) RSV engine taking over from the Futura lump which wouldn't run. Took it for an MOT on Friday and was amazed when it went straight through. Just advisories that the pads are getting a bit low which I knew about and am looking around for new items.

One item which confused me when I was riding around is the speedo. I posted before that it seemed to not be working but with a new battery it is fine up to about 60MPH after which it just shows 0. Given that it does work up to 60 I can't see how it could be the sensor as such - do they read the speed by counting holes in the wheel or something and could it just be a case of dirt? Can you clean them?

Well done on the mot
Im inclined to think it may be the instrument itself, not that this is an area I have much experience in. ..
Hopefully someone we be along soon with wisdom

The sensor is triggered by the bolts that hold the rear disk (never change them for anything but steel).

The Workshop manual tells you how to check the sensor and also the clearance between the sensor and the bolts.

I'd start by checking those things out - and any connectors in the circuit.

Well finally got around to checking the speed sensor - and it isn't an aprilia one which may be the issue. It is a PR12-2DN which a quick google will reveal is a 'AUTONICS PR12-4DN INDUCTIVE PROXIMITY SENSOR' which I guess should do the same job as the Aprilia item?

First question is has anyone tried using such a generic sensor sucessfully. Secondly what sort of clearance would be required between the sensor and the bolts - I assume looking at the spec sheet its 1-2mm and lastly should it be in some kind of rubber boot to prevent it from earthing or being affected by the swingarm itself?

Wayno did some fettling with a different sensor so his name may help in a search