Ok chaps and chapesses,

Mate is changing out his gearbox which is currently a cable drive to the speedo and the new one either has no sensor or not one he thinks he can use. He doesn't want to change instruments so I see two choices: Find a gismo that can connect to the end of the cable to mimic the cable drive from a new electric pickup (can't recall ever seeing or hearing of such a creature). Or tear the dash apart (this isn't a locost!) and get an electronic speedo fitted (possibly getting it converted to either use the existing dial fascia or have a reproduction made) which doesn't sound easy/cheap either.

Thoughts? Any other options? (sensible now folks

Thanks...

my koso dash is being fed with a signal from the back end of the old sierra speedo still attached to the cable
there is a magnet there ready for you , and in my case a suitable bracket to mount the koso sensor

took a bit of trail and error to work out the speedo calibration, but works ok

He won't have the cable but he still wants the old cable speedo so if's there's a way of doing that in reverse then top banana!

What gearbox is he using?

Think it might be a 6 speed from a volkswagen Mel (poss diesel van which is apparently bombproof - he's running north of 500 bhp!). I didn't get long to speak to him so that may be wrong - He's got a old T5 in at the moment

Would it be possible to use a sensor on the prop through some electronics to turn a small stepper motor which would act as the cable from the original box

You can do this with a stepper motor and a bit of electrickery.

Needs a simple circuit (Like this one) and a cheap stepper motor to connect to it. A bit of guesstimation is needed to work out the RPM of the speedo drive in the first place, but these circuits are pretty adjustable.

Provide a pulse with a hall effect sensor and it should be easy enough to get this working.

Cheers

Peter

As usual LCB provides the answers! Thanks guys...