it is a super cool dial...which dials going or are you podding it?
Mystery Tacho
- Thread starter Panky
- Start date
100% getting one in, very difficult to know what revs your doing in the van so never sure if I'm over stretching it or not. just need to find one as good looking as that
is there a make on it Mr P?
No markings at all, it was advertised as a Yakuza but there's no such thing as far as I can find
Your ears and the seat of your pants will tell you if the engine is having a hard time, for me it's just because I like the look of gauge and I've never seen another like it
...I think it's having a hard time - got a new 4.77 diff to put in over Winter, mines weirdly got a none Spacevan standard one in, goes like stink off the line though
Nice...found a few similar, the one Panky has has the needle at the bottom which makes it look factory. Would love one like that but think will have to settle for the centre needle type
Just make sure its for a 4 cylinder. Most aftermarket tachos have a switch for 4-6-8 cylinder settings. Larger VDO Tacho's have 5 or 6 dip switches on the back from memory, that need to be positioned correctly for number of cylinders and whether the motor is 2 or 4 stroke.
If salvaging a tacho that was original equipment on another car, take care. They are often set for a single use, often will say 4 - 6 - 8 Cyl on the gauge face. If no marking or you don't know what it's off be wary as it could read incorrectly, eg an 8 cylinder tacho on a 4 cylinder will show only 1/2 the actual RPM, while a 6 cylinder tacho will show 2/3 the RPM on a 4 cylinder.
Have a look at Panky's thread on Ted when he fitted the Tacho
Cheers Stephen
If salvaging a tacho that was original equipment on another car, take care. They are often set for a single use, often will say 4 - 6 - 8 Cyl on the gauge face. If no marking or you don't know what it's off be wary as it could read incorrectly, eg an 8 cylinder tacho on a 4 cylinder will show only 1/2 the actual RPM, while a 6 cylinder tacho will show 2/3 the RPM on a 4 cylinder.
Have a look at Panky's thread on Ted when he fitted the Tacho
Cheers Stephen
Hi. I am a non-Commer infiltrator! But also have one of these and I understand that Panky's is also not working yet... so this might be helpful.
My researches find that the poles are actually marked + (left as the photo without all the subsidiary lighting gubbins) and -.. and are insulated totally from the external rear body.
Under the blue/green rubber grommet exit are two variable resistors which can be turned.
Connecting + and - with 1.5V battery yields needle full movement.
Connecting blue and green wires with 1.5V battery yields needle movement to 2k-ish, or it trying to go backwards into stop.
Connecting to car (neg earth) as per yazaki diagram on other forums i.e. blue to coil/dizzy neg, yellow to coil pos, and black to earth.. and turning ignition on yields needle reversing itself to its stop. Seemd odd so haven't tried turning key to initiate starter! (red wiring omitted as it just complicates - its only dash lighting)
I also have a 6V stamp under the little 12V sticker on the reverse of the unit. (And my Yazaki box is stamped 6V)
No yazaki info gives ANY function for the green wire. But the grommet it comes out from has a stamp on my body saying "4 6 cyl" so could these be interchangeable for the larger engine?
If anyone has any further thoughts on what to test, do please continue the thread for benefit of Yazaki owners everywhere! My austin 7 is neg earth/6V.
Yazaki instructions (obviously for a different unit) connected.
A few images from inside attached.
My researches find that the poles are actually marked + (left as the photo without all the subsidiary lighting gubbins) and -.. and are insulated totally from the external rear body.
Under the blue/green rubber grommet exit are two variable resistors which can be turned.
Connecting + and - with 1.5V battery yields needle full movement.
Connecting blue and green wires with 1.5V battery yields needle movement to 2k-ish, or it trying to go backwards into stop.
Connecting to car (neg earth) as per yazaki diagram on other forums i.e. blue to coil/dizzy neg, yellow to coil pos, and black to earth.. and turning ignition on yields needle reversing itself to its stop. Seemd odd so haven't tried turning key to initiate starter! (red wiring omitted as it just complicates - its only dash lighting)
I also have a 6V stamp under the little 12V sticker on the reverse of the unit. (And my Yazaki box is stamped 6V)
No yazaki info gives ANY function for the green wire. But the grommet it comes out from has a stamp on my body saying "4 6 cyl" so could these be interchangeable for the larger engine?
If anyone has any further thoughts on what to test, do please continue the thread for benefit of Yazaki owners everywhere! My austin 7 is neg earth/6V.
Yazaki instructions (obviously for a different unit) connected.
A few images from inside attached.
Attachments
further to last, accessing speedycables website FAQ suggested just connect the yellow (i.e. a resistored wire from the positive post) to the dizzy/coil negative, and black to earth.
That WORKS the unit well... but it seems like it is over-reading [about 1500/1600 when it is at idle, and goes up to over 4000 revs when it feels more like 3000]
When I bypass the resistor (just in case that IS the 6V to 12V manufacturer conversion, and I need the 6V) it does pretty much the same.
But presently I have NEITHER of the blue or green wires connected from the 'heart' of the unit.
There are clearly two variable resistors under the grommet to enable trimming, but how does one know what to trim them to, other than knowing roughly what a slow tickover feels like!
That WORKS the unit well... but it seems like it is over-reading [about 1500/1600 when it is at idle, and goes up to over 4000 revs when it feels more like 3000]
When I bypass the resistor (just in case that IS the 6V to 12V manufacturer conversion, and I need the 6V) it does pretty much the same.
But presently I have NEITHER of the blue or green wires connected from the 'heart' of the unit.
There are clearly two variable resistors under the grommet to enable trimming, but how does one know what to trim them to, other than knowing roughly what a slow tickover feels like!
Excellent. I've just opened my gauge up and it's exactly the same as yours down to the 6v stamp under the label. There is a stamping by the grommet but it's illegible, I suspect it will be the same as yours though. I suppose the only way to set it up is to attach it to a car with a working tacho , either that or borrow another unit.
Just been out to have a fiddle. Soldered in a new resistor of the same rating as the broken one and lashed the tacho into Ted the Traveller as per JonE's method. I was able to compare the mystery tacho against Ted's installed one and the results are very similar to Jon's, tick over is pretty close - maybe 50rpm out at 750 indicated on Ted's gauge, but at a Ted 3000rpm it's just below 4000 on the mystery. It turns out that what we thought were variable resistors are in fact multiple contacts on the wires not used (maybe to set up for cylinder number variations) so not adjustment for zero and span as I'd thought. I cant see any other easy way of adjusting the reaction but could a higher rated resistor in the signal wire do the trick? any ideas
good good. I'm presuming your Commers are 12V too. So that is another variable to work out..i.e. that I'm using 6V.
Let me know if you try with other resistors.. I'm capable of soldering so could certainly try that this end.
I wonder if you ought to try with two in series and see what happens, up or down...
btw, I've sent something to speedycables about all this. Had one email response but nothing since! It might be too far out of living memory for technicians...
I have no tacho to compare to. What sort of rpm is the slowest 4 cylinder turning idle? 750 sounds very low...
Let me know if you try with other resistors.. I'm capable of soldering so could certainly try that this end.
I wonder if you ought to try with two in series and see what happens, up or down...
btw, I've sent something to speedycables about all this. Had one email response but nothing since! It might be too far out of living memory for technicians...
I have no tacho to compare to. What sort of rpm is the slowest 4 cylinder turning idle? 750 sounds very low...