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How do you know if your tachometer is going bad?

Posted by MPKaier

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How do you know if your tachometer is going bad? #1
MPKaier Mike Kaier Wilmington, DE, USA 1966 MG MGB	Posted: August 16, 2012 08:59PM Registered: 1 year ago Posts: 63

Hi All,

My 66 mgb heating problem appears to be cured. Radiator cleaned and flushed along with the fan removed and reinstalled in the correct direction. Yea. Now my tachometer is reaing fine at idle, but rolling down the highway at 65 or 70 the needle reads in the red zone and at 75 is all they way past red, but the engine sounds just fine and there is still plenty of power.

I know my timing is slightly advanced.

Do the tachometers just fail all of a sudden? Or is there an adjustment that can be done?

Thanks,
Mike

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Re: How do you know if your tachometer is going bad? #2
ClayJ Clay Johnston Mt. Olive, MS, USA 1972 MG MGB	Posted: August 16, 2012 09:06PM Registered: 7 years ago Posts: 7,358

Mike,
I would start by checking all the wiring connections at the tach and at the ignition to ensure all are clean and tight. Since this is a current sensing tach, it might be that a unusually high current is being pulled by the ignition, that needs to be checked, easy with a multi-meter in series at the coil.

There are some electrical components in the current sensing tachs that don't age well. A thermistor and a couple of capacitors. There are instructions here on the site to replace the commonly failing electric parts in the tach.

There are several shops in the country that will repair the tach if you wish to go that route.

Cheapest route might be to locate a used replacement. On a 66 I think you will need a current sensing tach with the external current loop.

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Re: How do you know if your tachometer is going bad? #3
ozieagle Herb Adler Geelong Victoria, Australia 1958 Wolseley 1500 "Wooly" 1966 MG MGB "Bl**dy B"	Posted: August 17, 2012 12:30AM Registered: 2 years ago Posts: 1,363

Clay is right.

If you are not electronically challenged, then this site gives full reco instructions.

http://www.sunbeamalpine.org/downloads/alpine_tach_repair_rev5.pdf

Herb

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Re: How do you know if your tachometer is going bad? #4
MPKaier Mike Kaier Wilmington, DE, USA 1966 MG MGB	Posted: August 17, 2012 07:17PM Registered: 1 year ago Posts: 63

Thanks, this is great information. It sounds and looks like a fix that I am capable of. Maybe I missed it in the instructions, but It mentions a kit that Tom put together but does not appear to give any information on where to purchase it.
Did I miss that?

Thanks,
Mike

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Re: How do you know if your tachometer is going bad? #5
ClayJ Clay Johnston Mt. Olive, MS, USA 1972 MG MGB	Posted: August 17, 2012 08:37PM Registered: 7 years ago Posts: 7,358

Might try contacting someone on that site. I picked up the parts at a local Radio Shack well as I remember.

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Re: How do you know if your tachometer is going bad? #6
MPKaier Mike Kaier Wilmington, DE, USA 1966 MG MGB	Posted: August 17, 2012 09:05PM Registered: 1 year ago Posts: 63

Radio Shack...of course...Thanks.

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