Bouncy Tachometer needle steady idle

sounds Chinese, last car from Kirk same thing, sent me 3 new ones, same thing.He finally took one to N. Hollywwod on his dime and it was perfect after that,].

The tach looks Brazilian or German tho.

First, clean up the electrical connections on BOTH sides of the coil.

Next, find the wire going from the coil to the tach and clean that connection.

Next, find the ground wire and the +12 volt wire for the tach and clean both connections AND the ground wire connection where it attaches to the frame ground.

If that doesn't cure it, then I would look at a new ignition module inside of the distributor, whatever that is.

If all that doesn't cure it, then it's time for a new tach, but I would suspect those other things, first.

@Gordon Nichols posted:

First, clean up the electrical connections on BOTH sides of the coil.

Next, find the wire going from the coil to the tach and clean that connection.

Next, find the ground wire and the +12 volt wire for the tach and clean both connections AND the ground wire connection where it attaches to the frame ground.

If that doesn't cure it, then I would look at a new ignition module inside of the distributor, whatever that is.

If all that doesn't cure it, then it's time for a new tach, but I would suspect those other things, first.

And for good measure, coat all of them with Craig Pro Gold.* I found this kit on Amazon that’s perfect for the auto diy-er.

Everything in it is useful except the Fader Lube, although there might be a use for that I haven’t discovered. (IMO, the Fader Lube is useless even for lubing faders. Maybe in a home studio or HiFi or something. Mixing a B-Way show is like playing a piano. If you couldn’t flick a fader and have it bounce off the top of the travel, it was considered “sticky.” We’d clean them with alcohol until they wouldn’t, then we’d just replace them. )

* I guess it’s called DeOxit Gold now. Old habits die hard.

Thanks. That is helpful. I’ll give it a try 🤞🏼

The gauges are Porsche 356 original parts. Although the tachometer is a bit of a hybrid. I needed to keep the electronics from the replica gauge because 356 have a cable driven tach, if I am remembering correctly. The replicas use the ignition coil to drive the tachometer. 🧌

Later 356C/912 had electric gauges.  But prices are indeed high now.  So I'm guessing electric guts in yours are from an OLD Brazilian or Chinese gauge?  They can be rebuilt with VDO parts but not-inexpensively.

My tachometer has acted peculiar twice so far.  During the first incident it was reading some 700 RPM too high and on the second incident the needle would drop to zero and bounce up and back down several times before returning to a normal reading.

My tachometer is an electronic VDO unit made in India.I think all the 356 VDO gauges are made in India these days.

Jason

@JasonC  Looks like you need to do the same as recommended to Colorjocky (see above).