Help with tach mechanism

[Tarantulahed504]

On my 1978 gs750e

After I finally got my carbs cleaned up, jetted and orings, reassembled etc. I came across another issue. that my tach was hanging at around 2k rpm and would move. I did some research on the forum. Pulled the cable to inspect for broken tang or inner cable itself. Found everything to be good and well lubed. I don't think it's an original cable. So then I decided it was time to dive in gauge cluster itself. I pulled the back off and the tachometer out. It was a little cobwebby but not all that bad and not corroded up or faded either. I pulled the metal ring face off, very carefully and slowly (much cursing during this bit). Tach needle didn't want to pop off but I got it eventually. Now I have the actual tach mechanism isolated but I don't have a clue what to do. It's not dirty and seems to be lubed up ok. I was thinking that maybe the female square drive is a little stripped out and the cable male square was spinning inside of it.

please help
thanks for your time

[Tarantulahed504]

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[Tarantulahed504]

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[Tarantulahed504]

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[Tarantulahed504]

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[Tarantulahed504]

Am I troubleshooting the wrong place
and should be up in the at the head when the drive gear and things are??

it just didn't seem like that by the symptoms

[Gorminrider]

you could put a long rod filed to square in your drilll to test. (im leery of a/c fields around these see below- a/c fields neutralize cheap magnets...)Good luck.

and now, my theory which is mine: Sometimes the not-so-permanent magnet in these tachs just fail in old age so there's not enough oomph to move needle against spring. That's pretty much hopeless. You might try to adjust the spring but goodbye accuracy.
All in all, apart from trying to flush old gluey grease from the bearings (carefully!- the dial paint can be washed off by weird carbcleaners and the like) so try simple solvent like kerosene or paint-thinner very carefully with a hypodermic etc.. don't make a mess.

IN FACT a droplet of sewing machine oil seems to scratch the itch to fix it as well as anything...

You can run the motor with speedo disconnected and see if the cable is spinning ok...sometimes at low speed a "stranded" cable will catch the housing making needle jump but that's not your problem apparently. I'd think there's be a clicking noise if the top end drive gear is broken or otherwise ##$%... another thing that makes the dial jump is when the spinning magnet touches the "bell housing" due to worn bearings. can often be heard.

[roeme]

Correct place.

Hanging tach needle is often caused by dried out lubration. When I encountered these symptoms, I removed the old gunk, and put WD-40 in - without taking off the face or needle.
This helped at first.

However, it has begun to hang again after a year, possibly because the WD-40 didn't stay in place (or didn't penetrate well), and cold temperatures.

Thanksfully, I drilled a small hole to be able to re-lubricate without opening the tach, but then again the mis-indication doesn't bother me too much, as I have more serious stuff to attend to.

Btw, an electric drill will help greatly with troubleshooting the issue, for spinning the tach.

[Tarantulahed504]

The tach wasn't jumping. It was hanging up at 2k once it hit it, and also wouldn't come back down to idle rpm.
The inner cable and housing seem to be fine and lubed. I don't believe it's the original so maybe it's the wrong part. Or length

so kerosine and sewing machine oil ???
where the needle gets reattached??

thanks

[mrbill5491]

The drive magnet can loose its magnatism over time and simply won't turn the the housing. I have several that are that way.

[Tarantulahed504]

The drive magnet can loose its magnatism over time and simply won't turn the the housing. I have several that are that way.

I hope hope that's not the case.....
after I clean and lube, try and spin it with a cordless drill. If it doesn't Climb all the way up. The magnet would be the culprit?
and there's no replacement part. I would have to source another used unit or go aftermarket ??
is that correct?

thanks again for all the help guys

[mrbill5491]

I hope hope that's not the case.....
after I clean and lube, try and spin it with a cordless drill. If it doesn't Climb all the way up. The magnet would be the culprit?
and there's no replacement part. I would have to source another used unit or go aftermarket ??
is that correct?

thanks again for all the help guys

Exactly....

[chuck hahn]

WD 40 IS NOT a lubricant. It is a WATER DISPLACEMENT agent. I evaporate away quickly.

[Gorminrider]

I hope hope that's not the case.....
after I clean and lube, try and spin it with a cordless drill. If it doesn't Climb all the way up. The magnet would be the culprit?
and there's no replacement part. I would have to source another used unit or go aftermarket ??
is that correct?

thanks again for all the help guys

You would need to check the max rpm of your drill of course...otherwise you could try an instrument rebuilder and see what they say. Suzuki used several different models of tach...ie: the ones from my T and E of the same year are not the same size...and idiot lights vary on various cc bikes etc etc. Ebay replacements can have the same issue as yours so be careful there....etc etc etc.
Tachs are not necessary anyways if you can hear your engine so you can just get used to ignoring it.

[max parsons]

Look up rewinding a GS1000 speedo.It might help.