1.8 k series speedo transducer question

Hi all, the rover k series standard speedo transducer.......

Can anyone explain to me how these work?

I have one open, it appears to have a magnetic cylinder, a pin that goes into the rotating unit on the gearbox, a little spring, ball bearing then just a connector on the top..
Thing is my speedo has stopped working, the transducer is in good condition and the pin in tact.
Dont understand it??

Thanks

not totally sure on this, but would think ball bearing goes into gearbox rotating unit to act as well, a bearing I guess. what it rests on in the gearbox is eccentric in its shape so as the gearbox rotates, the rotary motion of the gear box is translated into a linear motion via the ball bearing onto the pin, which then moves in and out through the magnetic cylinder, which then generates a small electric current which pulses in time with the rotation of the gearbox internals. The spring simply keeps the whole assembly in contact with the rotating surface. The current pulses can then be read by the ecu.

probly !