Jumpy tach needle strikes again

Here it is, back from the dead and it still wants to eat my brains.
Ok some history.
Shortly after doing my restore, let's say 2013 my tach started to get jumpy and then all of the sudden it went total exorcist on my and spun all around and broke off the needle.
I haven't had the time or money to replace it until now, it kind worked after it's death but was really an eyesore.
So, bought a used (not as much as mine was) Tach (nice and clean on the inside, spring looked good), brand new cable, even painted it all nice.
Took it out today for the test run and it was doing well, a little twitchy but nothing major.
Now on the highway between 3500 and 5000 rpm it likes to bounce around, like it bounces from 3500-5000 at an even throttle. But not continuously.
I'm so worried that I'm going to loose another (there aren't a lot of them left out there).
All the advice I see is to lube the cable, but it's lubed from the factory (I even shot some cable grease in there for good measure.

Can I save it? Do I need to call a priest? I can live with a jumpy needle so long as that's all it is.

 

so it is a new cable?
did it come with a paper saying it was lubed at the factory?

K-moe has mentioned something about the magnets in the tach I do not remember what it was.

also confirm it is properly seated in the motor and the tach my knurled nut on the tach loosened up and the tach was jumpy when i noticed it and tightened it it went away

 

I don't know the answer to your problem but that is a great opening line.........

 

Well... No... It did not.
And yes all mechanical parts look to be seated properly.
I understand that a mechanical tach spins a magnet that pulls on a metal cup that is spring tensioned to the needle.
But the only thing I know about magnets us that they make power for my bike and make hoverboards float.

 

pull the tach cable and lube it up good you should beable to pull the inner cable out spray it down and spray lube in side the outer cable

I will go out on a limb here what you need to do if it is the magnet it put a strong magnet on the speedo magnets to make it stronger you do not leave it there just charge it up some

How to Restore a Permanent Magnet | Sciencing

How to Make a Magnet Stronger | HowStuffWorks

something about stroking the magnet does the trick

 

The strength of the magnet is not going to cause the tach or speedometer to bounce erratically. If the magnet is weak, the tach will read low on rpm or the speedo will read low on mph.

The most likely issue is binding, either in the cable or the gauge. If the cable spinning meets any resistance, it will bind to a point and then suddenly let go creating a spring effect that will actually cause it to spin faster for a moment resulting in a momentary bounce in the gauge indicator.

Same is true for the delicate spring inside the tach. If there is binding and sudden release the inertia of the indicator will carry it past the actual point resulting in a bouncing erratic needle.

Cleaning, replacing the cable is a good place to start. If that does not solve the problem then cleaning the gauge bearing and re-lubing would be next on the list. Since the replacement gauge is not new, it is just as likely to have bearing issues as the old one.

 

Ok... How do I do this? Where are the bearings? Do I just spray lube into the port on the back of the tach where the cable screws in?

 

Has one of the faceplate screws fallen out? Have seen that before screw picked up by magnet causing tach to get goofy

 

no it is more in depth than that we have a thread on it but the photos have been lost