1990 JCB 3CX Tachometer.

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Rothers
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1990 JCB 3CX Tachometer.

Post #1 by Rothers » Tue Jun 05, 2018 1:44 pm

I have a 1990 3CX and the tachometer is not working.

Is the tacho on this model controlled electrinically by a sensor on the alternator?

Also, could anyone suggest the best method of fault finding please?

Thanks in advance.

Sam.


Whitlock 505
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Re: 1990 JCB 3CX Tachometer.

Post #2 by Whitlock 505 » Tue Jun 05, 2018 4:44 pm

Hi Sam

Have a look on the front of the timing case around the area of the alternator, if there is a little gearbox with a cable coming out then it is a cable drive, just overhauled a 1987 3cx and we replaced the cable and the tacho still worked, the old one had snapped and rusted away, what type of instrument cluster panel have you got?

Ian
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Re: 1990 JCB 3CX Tachometer.

Post #3 by topkit » Tue Jun 05, 2018 7:30 pm

I am pretty sure the later 1988 1989 onwards models were all electric, i have the same problem on my late 88 sitemaster, i took the unit out and there was no speedo cable everything was on a circuit board, If i get a chance i will remove it again and take some pics, i have a friend who is a circuit board guru and can normally find a faulty capacitor or resistors He recently sorted ny Fermec out pcb from terex about £400 all it was was a 19p resistor which he de soldered and replaced, most of the parts that are soldered into a pcb are generic so can be sourced quite easily.


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Rothers
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Re: 1990 JCB 3CX Tachometer.

Post #4 by Rothers » Wed Jun 06, 2018 10:26 am

Hi thanks for the replies!

Ian, I have the same instrument panel as the top one shown in your pictures.
I have had it out and there is no sign of anywhere to attach a mechanical drive cable so I’m sure it is electronic.

The temp gauge is not working either so it could be linked?

I had no lights but I got them all working now.

Thanks for the help.

Sam


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Re: 1990 JCB 3CX Tachometer.

Post #5 by topkit » Wed Jun 06, 2018 9:42 pm

It may be your temp sensor, have a look and see if there is one with a wire missing quite often the wires come off, i cant quite remember where the sensor s located.


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Re: 1990 JCB 3CX Tachometer.

Post #6 by Sailor57 » Thu Jul 04, 2019 5:17 pm

Hi, I'm new to this site and just bought a 1988 Jcb 3cx in early June the previous owner said it was ready for work, no leaks etc, etc. So far I haven't used it. I'm at present checking it over, transmission fluid milky pink, so probably not changed for years! No throttle, changed cable all ok now. Just bought a load of filters and oils from Greenshields (they have a 20% off deal for older machines. My main frustration is the tachometer which doesn't work, another lie from the previous owner! I have checked on here, bought a hard copy manual from ebay, but no diagrams of the wiring. No wires directly to the unit. I checked the 'w' stud on the alternator and that gives 7 volts at tick over. I can't see that jcb would use that anyway because owners would simply disconnect it to keep the hours low! I have uploaded some pics. Any info would be gratefully received. I'm in the West Sussex area, thank you, Garry
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Jeremy Rowland
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Re: 1990 JCB 3CX Tachometer.

Post #7 by Jeremy Rowland » Thu Jul 04, 2019 10:52 pm

Hi Garry and welcome :wave: hopefully somebody on here will be able to offer you some advice. :thumbup:

Jeremy


Sailor57
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Re: 1990 JCB 3CX Tachometer.

Post #8 by Sailor57 » Fri Jul 05, 2019 8:36 am

Thank you Jeremy :wave:


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Re: 1990 JCB 3CX Tachometer.

Post #9 by kaos » Fri Jul 05, 2019 10:27 am

Have you checked the downloads on this site? There is a JCB 3CX, 4CX, 214, 215, 217 Workshop Manual there, covering M/c no. 930000 onwards. I took a quick look, and the tachometer there is indeed driven from the W terminal of the alternator, see circuit diagram on page 156 of the PDF.

As for owners disconnecting it to keep the hours low, that would also apply to other methods. The only reasonable alternatives that I can think of for JCB at the time would have been a mechanical tach or an electronic one with a dedicated sensor, and these could just as readily have been disconnected.

Best of luck with your project.

--
Kári


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Re: 1990 JCB 3CX Tachometer.

Post #10 by Sailor57 » Fri Jul 05, 2019 1:24 pm

;) Hi kári, thank you for for reply, I have the manual for my machine, up to serial no. 400000. And have looked at the next one for project 8 machines and couldn't see anything I understood. Will look at the page you gave me and let you know. My machine is no. 342628

Thank you
Garry


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