thnking of mking a small circuit using IR transmoitter/receiver diode to cont pulses on a slotted wheel driven by the speedo (ford 4 speed escort exhast).

now when I took the speedo cable off, I notice that area has a bit of gearbox oil so wondering that this will be a problem for the optical sensors at some point - unless it was just oil from the speedo cable.

anyone know if the speedo drives dribbles a drop or 2 from time to time to keep the cable lubed up?

I have noticed a few drops of oil tends to work it's way up the cable.

Why not use a hall sensor though? The speedometer will already have a rotating magnet so it makes things even simpler.