Diesel tachometer senser (mechanically driven)

looks very similar to the rover pg1 gearbox one .

the gearbox is found on the 2 ltr T-sreries and diesel engines fitted to 220 420 600 and 800.

all the best.markj

The Eagle was used in a wide range of British trucks including ERF. Dealers may still have some old stock.

Thanks, will check this out.

Julian,

Yes, it's from an ERF E12 (12 litre Roller) I've tried a dealer or three, they all laugh, I've a few more scrapyards to ring today. I think you're confusing dealers of old to the ones today run by the bean counters. You're lucky if they have an oil filter on the shelf nowadays :-(

Julian.

Try Speedograph Richfield Ltd at

As an ex-electronics engineer by profession, I would offer the warning that the electrical output pulses would need to be of the correct amplitude and duration to "match" with whatever it is feeding into. Sorry if I am "teaching my granny to suck eggs", but thought that a comment in time may prevent you from spending money on something which may not work!

What about taking a feed from the alternator W terminal? Or have you already got a petrol tacho?

moray

"THE DOUGLAS STATIONARY ENGINE RESOURCE (admin)" wrote in message news: snipped-for-privacy@brightview.co.uk...

That's a fair point, and one that hadn't escaped my attention. The trouble is I don't know exactly how it works or what output to expect. It ''feel'' (when you turn it) like an old generator that used to rest on a bicycle tyre. I'm guessing that it's a simple AC alternator, frequency proportional to RPM? A fair assumption or not?

Cheers Julian.

There's no W terminal, already checked :-( The ERF EC's changed to the W terminal, mine is just pre W terminal.

I'm not in the least bit sure if a W terminal output would match that of the tacho genny that I have at the moment?

Julian.

PS, found a breakers in Darwin (not too far from me) with a few Rollers lying around - say I'm welcome to come and have a look-see.

Julian.

How many wires coming out of it ?. That is, is this an optical, hall effect or other magnetic sensing device internally. If you can get the lid off it, can you post a jpg somewhere so we can see the internals ?.

If it's two wire, then it probably uses a simple magnetic reluctance sensor. Otherwise, some electronics inside...

Regards,

Chris

It's a simple two wire jobby (non polarity sensitive) . I think it's probably two wire and not one wire because the truck does not use the chassis as a return circuit for electrical equipment. There's nothing fancy about it at all. Unfortunately it is assembled in a way that makes taking apart without damage impossible :-(

I've tested it with an AVO. So far I've spun it up with the cordless drill and measured Hz, Volts AC & DC but I've not found an output that seems to correlate with RPM. However this sort of thing isn't really by forte and don't really know what I should be looking for.

I've proved the integrity of the wiring between tacho genny and instrument panel (which is made of unobtanium) so I'm just problem solving by process of elimination really.

Thanks Julian.

It's not just a simple switch is it?

I've no idea if it's suitable but a number of VWs have an electric sensor that plugs into the gearbox, I think it's a hall sensor. The beauty is some of the vehicles using the gearbox have a cable drive and others the electric sensor which connects to the same gearbox fitting as the cable drive. The electric sensor unit is driven by a square shaft about 3mm AF which fits into the gearbox in the same way as a cable would. My VW has it and is a 1995 Passat. Might be adaptable.

I wouldn't expect a mechanical switch, but a hall sensor's a distinct possiblity.

If a ahll sensor then it should give an AC waveform when the shaft's rotated I would have thought, but how clean that signal would be or what amplitude I don't know - maybe an AVO's expecting a nice clean sine wave or something, and what the sensor throws out is a series of spikes... putting it on a 'scope might be the only way to truly test it.

It guess it could be a hall / solid state sensor with an open collector output, which would need a load resistor at the other end of the wire. To check this, are both leads the same colour and if not, what do you get if you measure the volts at the device the sensor plugs into ?. Also, what does the avo read on ohms range if you turn the shaft slowly by hand ?.

It's probably unlikely to be a mechanical contact switch as the life wouldn't be anything like good enough...

Regards,

Chris

Reed switches will take the number of operations required but might not be quite robust enough for use on an engine.

That is a distinct possibilty. This particular senor beinga two wire device it may not produce a sensible output unless it has the proper bias voltage/current.

Darwin ? Australia , or is there another Darwin I didn't know about ?

The proper Darwin - in Lancashire :-)

Julian.

That'll be Darwen then.