P38 speedo drive

[Tom.H]

Hi

I’ve got a P38 transfer box in my challenge truck.

I am planning on getting my vehicle through an IVA and therefore need some sort of speedo

Could anyone tell me whether the speedometer on a P38 runs electronically or mechanically from the transfer box?

I may be completely wrong .... Does the speedo even run of the transfer box ?

Cheers

Tom

[q-rover]

The signal for the speedometer is generated by the ABS.

Nothing to do with the transfer box.

[David Sparkes]

At this point you might be investigating a bicycle speedometer, with it's own trigger and sensor.

I can't give you exact details, but it is a common approach, used by people running Kit Cars, or cars with non-standard wheels and tyres.

Some form of Search is called for.

The one point I can alert you to, is that you have to know something about the effective rolling diameter of your tyres, and convert that to the size of a bicycle wheel, so you can make sure the bicycle computer can accommodate that size.

There might be alternative methods of solving the 'speedo drive' problem, but the bicycle computer was the one that sprang immediately to my mind.

Good luck.

[Tom.H]

Cheers for your help.

I did think using a bicycle speedometer but the IVA don’t allow them to be used.

It seems the only way to do it is to buy an electronic speedometer and run it of the props haft or something.

Sadly there not cheap.

The best I’ve found is one for £70, I then need to buy the sensor and magnet

on top of that.

[David Sparkes]

Cheers for your help.

I did think using a bicycle speedometer but the IVA don’t allow them to be used.

I didn't know that!! Serves me right for repeating what I'd seen others suggest, and tried myself when I had non-standard wheels and tyres on a car, thus getting a slight misread on the standard speedo.

Good Luck.