I've currently gone through 2 speedo sensors for my smiths telemetrix gauges due to as far as I can tell, the vibration of the mount causing it to come into contact with the prop shaft bolt heads. I'm currently redesigning the mounting system to stop this however I'd still like to stop having to fork out £50 every time something catches for a new sensor. I've read that smiths gauges use an inductive proximity sensor to provide the signal and that these can be picked up cheaply anywhere. I've seen this one below that looks suitable, my only question is will the output of 300ma be suitable? I think I've read that the official smiths sensor outputs 100ma?


LJ12A3-4-Z/BY Inductive Proximity Sensor Detection Switch PNP DC6-36V, UK Seller

if its current output, then 300 will be fine, (it will be the max rating)
since its just for speedo, I would try one.
if it were for abs / engine timing / anything critical, then just use the original spec part.

note, there are about 50 types of proximity / hall effect sensors, some digital, some analogue , some that induce the magnetic field, others that respond to magnets

I wouldn't recommend cheap sensors on eBay from China. You could be putting your equipment at risk. Take a look at CONTRINEX. They are Swiss made and usually priced lower than market leaders TURCK & Banner.

http://www.clrwtr.com/CONTRINEX.htm

Just a thought, are the bolt holes on the diff flange not on a rectangular pattern (ie unevenly spaced on the PCD)

Your sensor needs to be adjusted to between 1 and 2mm from the bolt heads, so depending on how your sensor is aligned is possible that some of the bolts could be getting too close, but even if this is not the case the uneven spacing will give an uneven signal to the gauge...

Can you not use a sender driven by the gearbox?