OK, question for the Tach Boys...

[pbanders]

I see we've got some brave souls doing some tach hacks, so while you're at it, can any of you comment on the cause behind the famous 914 "bouncing tach" problem. What I'm talking about is the overshoot/undershoot problem you see on a lot of 914 tachs (mine, for example) when rapidly changing engine speed. I talked to PA Speedo, they told me that it was due to a "broken mechanical damper" - just guessing, is this the classic aluminum tab/permanent magnet gap thing? Is it obvious what's shot? Is it repairable or does it need new parts (presumably, available only to places like PAS and NHS)? Thanks....

[914GT]

Brad

I suppose I'm one of the 'tach boys' who does not have the answer but maybe something here to ponder. Don't know much about the meter movement and mechanical dampers, the speedo shop must know what they're talking about if they say they break. The meters have something to mechanically slow the response of the needle to make it react smoothly, and average-out the noise and jitter coming into it. That said, I noticed that mine would do some really odd things when I didn't put a signal into it that it liked. I could get some overshoot by quickly changing the frequency, and I can do that faster than a real engine can with a signal generator. What I'm wondering is - assuming you've got it hooked up to a stock ignition - could this be caused by a bad part in the ignition? Specifically a bad condensor or coil causing too much ringing which sends some abnormal garbage at the tach?

[pbanders]

Yes, it's possible it could be caused by a bad condenser or coil. But I've changed the coil, condenser, points (then I eventually replaced them with a Crane), etc., etc., over the 20+ years I've owned the car, and none of them had the slightest effect on the tach "bouncing" problem which I've been living with since I first got it. So, I'm guessing it's something with the tach itself.

[Mark Henry]

I don't care how original my teen is, so I installed an AutoMeter Monster tach, fits almost perfect. The thing is like a rock, I can downshift from 5000rpm and you would think I was turning a switch.
Instant, no bounce and IMO it looks cool.

[Bob Bischoff]

I'm with Mark on this one. I modified and calibrated my tach for a V8 conversion. Spent about 25 cents to change this for the V8. It works great but I would not spend the money that it cost to have this done at a speedometer shop. I think they charge about what a aftermarket tach cost new. The autometer tach would be the only way to go.

Bob

[Dave at Pelican Parts]

BTW, bad points and a bad condensor can indeed cause the "bouncing tach syndrome". Don't know why, but I've seen it.

--DD

[chrisreale]

Mine bounces. I have a working pertronix, and a good coil, so I think it is internal to the tach itself.

[Kenny Powell]

Sometimes a loose or corroded tach wire to coil can cause this problem.................corrected mine! hopefully that's it!

[Bleyseng]

Also, if you take the tach apart and clean the internals of all dirt and crud it works alot better.
Geoff