My tach needle has started jumping all over the place when car started. Not all the time, however. It will settle down and act correctly. Do not have a tach filter presently, but have one on order and will be replacing in a week - I know, I could build one cheaper, if I knew how to do that. Should I just leave the thing alone for now or disconnect until the filter comes in. If the jumping around is due to stray electrical signals, do not want to fry the tach board. Replaced that once already years ago and see no reason to kill it.

 

Larry,

It could be the board, or it could be a signal issue. You might want to go out to the distributor and make sure the connector is on good, or that there is not an issue with the wire.

It could also be an issue in the car either with the clips that make contact with the stud on the tach, the pinch connector on the back of the housing or the printed circuit on the back of the cluster.

Willcox

 

this occured with mine when the tach filter ? wasnt attached to the engine block thereby it had NO GROUND. (engine swap- long story) I installed a seperate ground wire , bouncing stopped. I am assuming the filter is the in-line thing about 1/2" diameter, 1.5 inches long.

 

You can also get this if you have a plug lead arcing/shorting on the distributor cap.

 

Turns out it was a battery terminal that was not tight. When I replaced the alternator recently, I took off a terminal and when re-attaching it, I did a poor job and it was loose. Also the reason why I intermittently could not start the car and had to jump it. Putting the jumpers on would make the connection enough and it would run fine until vibration, etc. caused it to loosen up again. Learned my lesson.

 

My 76 tach from day one last fall owning it was not smooth in operation. It worked but when accelerating it sometimes bounced a little and in general wasn't the greatest tach I ever saw. Besides, with my height, I have to look through the wheel spokes to see it and in my year the spokes take a fair amount of the view from both speedo and tach. It quit the other day, the tach. I traced the wire to the distributor, jiggled it to see if the signal wire with the filter was attached and it seemed to be. So, I said to heck with it, bought a 3 3/4" aftermarket tach and took it in to have that installed inside the car this morning.

The mechanic in fifteen minutes took the attachment clip off where the signal wire leaves the distributor and found that inside the bracket somehow the wire was broken. he soldered it in place correctly, mounted the filter on the intake Man. I believe correctly and then called and said "are you sure you want an aftermarket tach?" I said, no, not if it's working well.

It is smooth as a baby's butt now in operation and that wire inside the attachment must have been at times making less than full contract. Sure works good now and was a whopping $29 fee.

I'll save the aftermarket tach on the shelf. You never know.

Happy it's working better than any time since I've owned it. I thought Vette C3 tachs just sucked....turns out: not so.

Lance