Twitchy Tach

The last time I posted about this, I had just received my 4th tach from Kirk...all under warranty. This one did better that all the others, but it finally started twitching and jumping just like the others. So, I sent it off to North Hollywood Speedometer for the genuine VDO fix. Actually, I sent them the tach out of Black Betty too, because it was starting to act up. The total cost with shipping to repair each of them was $196.39. It's so nice to finally have a tach that works so perfectly!
Troy

Ive been driving with a jumpy tack all summer. the other day, while at a stoplight i finally reached under the dash and pull the plug. id rather have a dead tach than one jumping all over the place. i have three extra (jumpy) lying around... i should bite the bullet and get at least one of them off to hollywood.

kirk had mine done there and it has jumped once

should read hasnt jumped/twitched since.

Has anyone had any experience with Palo Alto Speedometer?

Dang shame, that. So twitchy is turned itself about 90 degrees to the left! :)

Reads low too, sounds like. GREAT engine noise though! At idle it harumphs like a 350 small block.

BTW, the Classic Instruments 3 3/8 tach in Bridget bobs about just like yours. Bought a new five-incher (proper TD size) and crossing me fingers about it.

You Ed you may be right. I've never heard an engine sound so good at 0 RPM.

You could try a pullup resistor on the tach signal wire. 100k Ohm 1/4 watt, from signal wire to +12V. Assuming signal is coming from neg coil terminal.

Or try a low pass filter on the signal wire. A 100k Ohm 1/4 watt resistor between signal wire and tach's signal terminal and a 0.005uF capacitor between tach's signal terminal and ground.

No guarantees since I have no idea what your outputs and expected inputs are, but it'd only cost a $1 at Radioshack and some time.

Just a thought but have you checked the ground. I my reading/research over at the Samba jumping tach needle is sometimes blamed on a bad ground connection.

Try running a second ground to the tach for a test.

I installed a second ground on my second tach, and every single one since then. I do not have a ground strap installed from the transmission to the frame, but dont think that would change anything concerning the tachometer.

I guess you can fool w/ the electronics, if you know how, but the true fix is to trash the cheap innards, and go VDO, Hollywood Speedos. that's how I got mine to work right.

The tach Kirk put in my VS not only twitched, it jumped like a Mexican Bean - I had my local Porsche mechanic (a real one; German trained) put his "wiring expert" under the dash and after he stopped laughing, he did some quick (less than an hour) rewiring to include even correcting the Ground! The result: I've driven it for a year and a half, put over 6,000 miles on it and the Tach has NEVER resumed the Dancing Twitch! Fortunately I did this BEFORE taking it down to Palo Alto Speedo and spending several hundred $ exchanging the innerds. Don't get me wrong - PA Speedo is a GREAT shop and they do GREAT work, but the $90 I gave to my mechanic sure beat the bejeezus out of what I would have otherwise spent.....plus the projected "down-time" of up to 2 weeks.

More often than not, electrical problems can be traced to ground problem. Alan

Let me guess - $5 for correcting the ground problem. $85 for knowing where and how to correct the ground problem.

At least in my case (5 times now), the twitchy tack problem was not a ground problem and the diode fix simply didn't work.

The twitchy tack issue is Kirk's biggest headache and he has had the tachs re-designed several times (in China) with no luck. Judging from my experience, I'm guessing the failure rate is probably close to 80%.

I think he just needs to add the $200 North Hollywood Speedometer VDO fix to the price of his cars. Or offer a "non-twitchy tach" option for an additional $200.
Troy

Absolutely; that's a legendary problem in these cars. Mine came bad straight from Kirk's shop when new. Kirk exchanged it once and worked fine for a while; then died. I went the VDO/North Hollywood route years ago and have never looked back.