71 Tac Question

[stubbfarmer]

I have not been here for a long time. hope someone can help with my problem. I have a 71 with a HEI distributer. I ruined two tac's before I found out the original tac's will only work with a point distributer. Does anyone know if someone makes a Tac that will work with the HEI distributer or if there is a way to make the original still work with it? Thanks for any help,

[stubbfarmer]

I am an old guy and not to tec smart. I did a search and found posts that talk about a tac resister or fuse from newer cars does that fix my problem? Thanks for helping.

[LockDoc]

Originally Posted by stubbfarmer

I have not been here for a long time. hope someone can help with my problem. I have a 71 with a HEI distributer. I ruined two tac's before I found out the original tac's will only work with a point distributer. Does anyone know if someone makes a Tac that will work with the HEI distributer or if there is a way to make the original still work with it? Thanks for any help,

Not sure where you read that information. I have used at least 5 original tachs with HEI distributors with no problems, both 6 cylinder and V8. I would say you have some other problem with your electrical system causing the problem or you are not getting it hooked up correctly. Even if you added a resistor it wouldn't cure the problem you are experiencing.

LockDoc
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[Grumpy old man]

Truck shop - ebay listing

ONE NEW TACHOMETER FOR YOUR 1967 THRU 1972 CHEVROLET GMC TRUCK, WILL WORK WITH POINTS OR HEI IGNITION SYSTEMS. WE ARE THE MANUFACTURER AND YOU ARE BUYING DIRECT. SHIPS TO LOWER 48 STATES ONLY.

https://www.scribd.com/fullscreen/57...jcbazlklxtunnw

[pjmoreland]

I have also run both original and reproduction tachs with HEI without any issues. That being said, I have seen these filters listed for sale on various websites. I haven't ever used one, but the warning below is somewhat intimidating.

https://www.classicparts.com/mobile/...ctinfo/24-736/

[stubbfarmer]

Thank you all for your replies and help. I have an aftermarket wiring harness (I think it is Painless but I bought it several years ago) and the dash guage unit is the repo from LCM. I burned up two Tac's and figured I needed to find someone smarter than me for help. I called LCM or the supplier I do not remember which and they told me the original tac would not work with HEI.

[Palf70Step]

I have a factory tach and it is not right with the HEI. Have tried the resistor thing shown and it is still off. I have heard some folks they will work and others can never get them accurate. Mine is close on low RPMs, but the higher up the more off it gets. Like today, with a 3.08 gear rear, it showed me doing 3500 RPM's at 70 MPH, but at idle it seems accurate. I am building a custom dash anyways, so I'll eventually replace it with one that is more accurate

[Smitty]

Years ago when I first acquired the cluster I am now using. I took it to a local speedometer repair shop and had them check the gauges, told them that I had an HEI distributor. Don"t know if they adjusted anything. But it works well. It was originally in a C-60.

[stubbfarmer]

Originally Posted by Grumpy old man

Truck shop - ebay listing

ONE NEW TACHOMETER FOR YOUR 1967 THRU 1972 CHEVROLET GMC TRUCK, WILL WORK WITH POINTS OR HEI IGNITION SYSTEMS. WE ARE THE MANUFACTURER AND YOU ARE BUYING DIRECT. SHIPS TO LOWER 48 STATES ONLY.

https://www.scribd.com/fullscreen/57...jcbazlklxtunnw

Here is what I have learned. I found the e-bay listing and looked at it. I called the The Truck Shop in Orange Ca from the above quote. I talked with their tec guy and he said about 80% of the time an original tac will work with a HEI distributor but the other 20% they won't and will burn up the Tac. He talked about it being mixing 60's and 90's technology. He said the solution was to either go back to a points distributor with a Pertronix electronic ignition conversion or a MSD distributor. So my plan is to try a point distributor with the conversion. I did not get an answer as to why the e-bay listing says it will work while the tec said it might not. He did say that since my distributer had burned up two tac's it would probably burn up a new tac also. He said there was no way to know what HEI distributor would work with a tac and what one would not. Thanks everyone for all your help.

[Dieselwrencher]

Originally Posted by Palf70Step

I have a factory tach and it is not right with the HEI. Have tried the resistor thing shown and it is still off. I have heard some folks they will work and others can never get them accurate. Mine is close on low RPMs, but the higher up the more off it gets. Like today, with a 3.08 gear rear, it showed me doing 3500 RPM's at 70 MPH, but at idle it seems accurate. I am building a custom dash anyways, so I'll eventually replace it with one that is more accurate

I just picked up a 72 GMC Sierra Grande Longhorn in December. It has a carb'd Vortec 454 with a HEI, 3:54 gears and 265's. The factory tach works exactly as you describe. I'm wondering if the filter will solve the issue? I might have to give it a try.

[LockDoc]

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I would call these guys.

https://www.cajuntachshop.com/

Not only can they repair your tach but I bet they can make it work with an HEI distributor too.

I bought a 6 cylinder board from them and installed it in one of my non working V8 tachs. Worked good in my '67 with a 250 I6.

Knowledgeable people.

LockDoc