Porsche 930 speedo pickup

[CraigB]

Hi all,
is it possible to use the original Porsche speedo pickup in a hall effect speedo setup? Does it work this way or some bespoke German method?

This is a quote from the 930 workshop manual concerning testing the pickup. After the cockup with the release bearing I did the bloke thing and found an instruction book

Disconnect the flat male plugs at the connector in the tunnel and connect a test buzzer to the wires leading back. Lift the car at rear axle and turn right wheel by hand. Lock left rear wheel. The buzzer must sound off 8 times for each two revolutions of the wheel. If not replace the sensor.

The left rear wheel need not be locked, if the car is equipped with a Limited Slip Differential. In this case the buzzer sounds off 8 times for each one revolution.

With 1 wheel locked the diff will rotate at 1/2 speed is that correct? so the speedo should be set to an 8 pulse per wheel rotation setting? or am I reading it the wrong way around?

[Russ Noble]

Hi Craig,

The plate with the 8 magnets is mounted on the diff housing. The speed of the diff housing does not change. With an open diff if you stop one wheel the other wheel will turn twice per diff housing revolution. With the open diff the only way you can get an accurate reading is to stop one wheel. With an LSD there is no need to stop one wheel because both are positively locked together.

Cheers,

[CraigB]

Thanks Russ,
so if I set my speedo to an eight signals per rotation input and relevant tyre size that should work Many thanks. I am assuming it is a compatible signal to "hall effect" sensors.