Wacky Tach

[Marty Rogan]

A little background on the car. This is my early '71. It has a stock coil and a Pertronix ignitor, in a stock distributor.

The tach will climb as normal till about 5500 to 5800, then it falls to practically zero. When you shift it climbs again as normal. All the connections are good. I have checked the grounds. I can't find anything that appears to be wrong.

Has anybody out there had this problem? Any ideas on how to fix this, or is the tach gone bad?

TIA,

Marty

[Arne]

Marty, if the car is still running fine (i.e. - no change in the spark), I suspect the tach is going. The one in my yellow car does odd things lately, and it's not even consistent. Sometimes it seems fine, then suddenly it will start reading about 1/3 of what it should, then it may just float around at random. During all this the engine (with ZX dizzy, E12-80 module) is running fine. Once when I turned the key on it pegged the needle past the red, but later that day it was fine again. These old things can be a bit fussy.

You might PM Escanlon, he has a great schematic of the circuitry inside the tach, complete with types of semi-conductors used. Using that diagram, someone who knows electronics should be able to repair one.

[Marty Rogan]

Marty, if the car is still running fine (i.e. - no change in the spark), I suspect the tach is going. The one in my yellow car does odd things lately, and it's not even consistent. Sometimes it seems fine, then suddenly it will start reading about 1/3 of what it should, then it may just float around at random. During all this the engine (with ZX dizzy, E12-80 module) is running fine. Once when I turned the key on it pegged the needle past the red, but later that day it was fine again. These old things can be a bit fussy.

You might PM Escanlon, he has a great schematic of the circuitry inside the tach, complete with types of semi-conductors used. Using that diagram, someone who knows electronics should be able to repair one.

The runs great. You can hear the engine continue to pull hard after the tach falls off the cliff. It is a little discomforting to not know the real RPM's since this is my track car.

E has helped me out with some electrical issues, and he is very good. Unfortunately, I am not so good with electrical stuff, as E can verify. On my last project, We had to break out the old "Wiring for Dummies" book to get me through, right E? !!

If the fix involves digging into the elctonics inside, I may be better off just replacing it. I didn't want to toss it aside if there is a simple fix though.

Does anyone know of a plug and play tach replacement that looks pretty close to the original look? I know there won't be an exact replacement, but it should not stick out like a sore thumb.

Marty

[Arne]

I've heard of folks using the Autometer 3990, but don't know how difficult it may be to mount nicely. And you lose your turn signal indicators, of course. But if it's track only that probably isn't an issue. Here's one on eBay now:

http://cgi.ebay.com/ebaymotors/AutoMeter-3990-Sport-Comp-5-In-Dash-Tachometer_W0QQcmdZViewItemQQcategoryZ33679QQihZ019QQitemZ8059770340QQrdZ1QQsspagenameZWDVW

[EScanlon]

...snip...

E has helped me out with some electrical issues, and he is very good. Unfortunately, I am not so good with electrical stuff, as E can verify. On my last project, We had to break out the old "Wiring for Dummies" book to get me through, right E? !!

...snip...

In my best Sgt Shultz: "Nutting, I know NUTT-ING!!"

As far as your tach, from talking to the electronic expert (who does work off schematic plans) after 30+ years a heat related failure of a diode or capacitor is not only NOT unusual, it's almost to be expected.

So, let's canvas around to find you a proper replacement. Yours is a "4-Wire" isn't it?

If it is a 4-Wire, instead of pitching the bad one, can I trouble you to send it to me? I've been looking for one with the exact symptoms you've described so that my friend can get in there and help me (us) identify a proper replacement and repair. I have my spare tach, which is in good working condition, the schematic, now I need one that is failing /has failed as yours is. With those 3 items, Gary (not beandip) says he can trouble shoot and help make more reliable.

E

[Arne]

Hey E, I'll swap the tach from my parts car into the yellow car before I sell it and you can try mine too, if you want.

P.S. - There may be people on this site too young to remember the good Sgt. Unfortunately, I'm not one of them.

[Marty Rogan]

In my best Sgt Shultz: "Nutting, I know NUTT-ING!!"

As far as your tach, from talking to the electronic expert (who does work off schematic plans) after 30+ years a heat related failure of a diode or capacitor is not only NOT unusual, it's almost to be expected.

Instead of pitching the bad one, can I trouble you to send it to me? I've been kind of looking for one with the exact symptoms you've described so that my friend can get in there and help me (us) identify a proper replacement and repair. I have my spare tach, which is in good working condition, the schematic, now I need one that is failing /has failed as yours is. With those 3 items, Gary (not beandip) says he can trouble shoot and help make more reliable.

E

I rarely, if ever pitch anything from these old cars. In fact I am collecting the original parts that I am missing (steel fan, steering wheel, etc.) to put it back original once it is retired from track duty. Maybe we could work something out though. I would be glad to loan it to you to support the cause, if you send it back repaired some day. How does that sound to you? In the short term, I just need a tach that works!

Marty

[Marty Rogan]

I rarely, if ever pitch anything from these old cars. In fact I am collecting the original parts that I am missing (steel fan, steering wheel, etc.) to put it back original once it is retired from track duty. Maybe we could work something out though. I would be glad to loan it to you to support the cause, if you send it back repaired some day. How does that sound to you? In the short term, I just need a tach that works!

Marty

On that note, does anyone have an early tack for a 70/71 in good working condition that they want to sell?

Marty

[EScanlon]

Whether it's Arne's or Marty's, or both, the intent is to troubleshoot the operation (feeding a signal is not a problem for Gary) while comparing to one that is working, then identify the bad / failing / potentially bad components and then replace with current / fresh / updated parts in order to effect a sound repair and a procedure for repairing / updating other items.

Those that are involved in this initial phase will more than likely be repaired and returned, I'm venturing to say free or very cheaply for the sake of research. Later ones would have that service done for a fee...to offset costs etc.

I'm not looking for "It's broke, and I don't know what broke!" samples, but rather as Marty posted "The tach ...as normal till about 5500 to 5800, then it falls to practically zero. When you shift ...again as normal. ... I can't find anything that appears to be wrong."

Since I'm looking to fund the research and repair out of change found in my other cars, I can't afford to buy them from folks, nor pay for shipping to and back (sorry, this is a very thin shoe-string). I also don't need 30+ samples either.

Gary tells me that he only needs one or two that are failing as described, a good one (my spare) and the schematic and his shop. Gary has designed, built and sold some very high-end sound amplifiers and other electronic gizmo's, so I trust his feelings on the subject.

The end result for us as a club, is to have a reliable REPAIR and UPGRADE procedure, which we can then have an electronic technician read and use to repair the tach's we send to him.

FWIW

E

[Marty Rogan]

Whether it's Arne's or Marty's, or both, the intent is to troubleshoot the operation (feeding a signal is not a problem for Gary) while comparing to one that is working, then identify the bad / failing / potentially bad components and then replace with current / fresh / updated parts in order to effect a sound repair and a procedure for repairing / updating other items.

Those that are involved in this initial phase will more than likely be repaired and returned, I'm venturing to say free or very cheaply for the sake of research. Later ones would have that service done for a fee...to offset costs etc.

I'm not looking for "It's broke, and I don't know what broke!" samples, but rather as Marty posted "The tach ...as normal till about 5500 to 5800, then it falls to practically zero. When you shift ...again as normal. ... I can't find anything that appears to be wrong."

Since I'm looking to fund the research and repair out of change found in my other cars, I can't afford to buy them from folks, nor pay for shipping to and back (sorry, this is a very thin shoe-string). I also don't need 30+ samples either.

Gary tells me that he only needs one or two that are failing as described, a good one (my spare) and the schematic and his shop. Gary has designed, built and sold some very high-end sound amplifiers and other electronic gizmo's, so I trust his feelings on the subject.

The end result for us as a club, is to have a reliable REPAIR and UPGRADE procedure, which we can then have an electronic technician read and use to repair the tach's we send to him.

FWIW

E

E,

I certainly don't have a problem donating mine to help with the research. I just need to get a working one before I pull it out. As soon as I get one, or it goes into storage, whichever comes first, I will ship it to you.

Marty

[EScanlon]

Excellent! And thanks!

You'll be getting it back, to use as a spare or...

E

[Arne]

Understood, E. If you get to the point that you want mine for further testing on what appears to be my heat-related issues, let me know. I'll be happy to get it to you.