CO WTB - NOS or perfect used tach dash circuit board

[scoyote]

My tach is reading wrong and there was a little break in the circuit board when I installed it and I'm guessing that little break is causing the tach to not get the proper electric current.....that is my guess.

So, I'm looking for a NOS or a good used circuit board or if not available then where is the best place to purchase a replacement (besides LMC)?

[john]

I would check further, the tach doesn't use the printed circuit. Just trying to help.

[72BlckButy]

The tach runs off a harness that stretchs from the tach and the rotor/hei dist. depending on your application.

[scoyote]

Hmmmm, then it sounds like it's not the printed circuit then.....it must be the tach itself.

I have a brand new Painless Wiring harness installed.....so the wires and connections are good......that really only leaves one thing then.

The tach I purchased (from this board) doesn't work correctly.

It's a 8 cylinder tach......it just reads several hundred rpms low all the time.

So.....that changes things

[PT'S 70 CST]

Take the tach out of the cluster and hook up to 12 V to the dizzy and your tach wire to the dizzy and ground it out good and check like that to see if it is indeed the tach. I hope this helps.


PT

[sameyrasmea72]

I thought there was a way to calibrate the tach.

[Livrat]

I may be wrong but from my experience the factory tachs were not very accurate from the begginning.

I decided one day to test 7 factory tachs side by side, hooked them up one at a time next to a digital tachometer and every one read different.. some way high.. others way low.. only one was close..

I would consider a couple hundred RPM's slow within tolerances.

I view a factory tach as a fancly hole plugger in the center of the dash with a needle that moves and by no means a way to know the real RPM's.

[chipflyer]

Its common for them to be off. If you have added HEI it makes it even worse as the pulse is different. Some add an EBAY tach filter like the one in the link and claim it helps. Haven't tried it yet myself.

Jeff

[olblue60@aol.com]

WOW, what a disapointment! I finished refurbishing a tack vac for my 67 panel, and after all the money I spent, It probably wont work right?

[70LonghornCST]

A while back I purchased an NOS fusebox/inside harness from a guy who works for American Autowire full time as an electical engineer, and buys and sells NOS parts on the side. He told me that since am using an HEI distributer, I did indeed need a tach filter. I posted a thread here to get some second opinions from some of our many years of experience on this board. I was told by many that a tach filter was not needed. I installed it and it worked perfect. It acted similar to my 2006 Silverado in terms of readings at idle and reving little by little. Of course, the tach I was testing was NOS.

So, if yours does not work properly, you might try that tach filter. It is said to be required by some if you are using an HEI. If not, it has to be the tach.

[olblue60@aol.com]

The tach filter is encourging. I have always wondered why people have steered clear of the aftermarket tachs with new electronics.

[scoyote]

Wow.....I started reading about tach adapters on Jegs and Mallory and MSD websites and from what I see....I NEED to have one since I upgraded to HEI and I'm running an "old school" tach.

but, now the question about accuracy becomes an issue.

Why put a tach adapter on if the tach doesn't read properly because of the way it was built back then?

So......when I was building my dash I really wanted the "in dash" tach and now I'm hearing that it's a piece of junk?

If that is the case......why bother at all?

Might be looking for other options....and probably need to change the title of this thread too ;-)

[chipflyer]

When GM went to HEI, the tach filter was necessary to filter out the high frequency noise from the HEI so the tach gives a steadier reading. Our trucks didn't have HEI originally and the old dizzy/coil setup probably worked pretty good way back then. Now everyone adds the tach to their HEI truck but not the filter and then complains about the tach not being accurate. All the GM vehicles that came with HEI (73 and up) had the little tach filter. I wouldn't call the original tach a "piece of junk", but it is just a show piece and has no real use in a daily driver.

Jeff

[70LonghornCST]

In some cases, yes, they are nothing more than like twinkling lights on a Christmas tree: nice to look at but not much more as accuracy can be an issue. But in other cases, they can, and do work quite well. Not new school by any means, but still functional. With that said, you only really need one if you are restoring a truck that originally had one or are merely into adding as many factory options as possible. It's more of a preference than a need, I would think.

[scoyote]

Well, it's sorta a need for me because I'm running the Turbo Hydro 350 which is a 3 speed and now and then I hope on the big road and want to kinda watch my rpm's so I'm not straining it too much.

Right now I have no idea how many rpm's I'm turning when I'm at 65 mph.

Says I'm at close to 5 grand but that isn't correct so I am trying to get it to read properly....or at least within reason.

I like the factory look, might need to look into a factory replacement that will fit that hole and still work with the HEI distributor.

It's that or pop another one on the dash or the steering column or????

I was trying to avoid that.

Which brings up another topic....does anyone make an aftermarket tach that works with HEI and fits our blazers?

[70cst]

Originally Posted by scoyote

My tach is reading wrong and there was a little break in the circuit board when I installed it and I'm guessing that little break is causing the tach to not get the proper electric current.....that is my guess.

So, I'm looking for a NOS or a good used circuit board or if not available then where is the best place to purchase a replacement (besides LMC)?

Ok all...lets see if we can find a good ccircuit board for scoyote.

[scoyote]

Actually now I'm thinking I don't need a circuit board but a tach that reads from an HEI system.

And a tach filter for the existing tach.

I can't change the title or move the thread but I did alert the mods to let them know that this has turned away from the original WTB thread.

So.....where can I get a tach that fits the dash on a 72 blazer but reads from HEI?

[Lemield]

Originally Posted by scoyote

Actually now I'm thinking I don't need a circuit board but a tach that reads from an HEI system.

And a tach filter for the existing tach.

I can't change the title or move the thread but I did alert the mods to let them know that this has turned away from the original WTB thread.

So.....where can I get a tach that fits the dash on a 72 blazer but reads from HEI?

I have the factory type tachometers in both of my trucks that I installed. I am running an MSD 6AL box on my CST with an MSD distributor....tach reads fine. On my C20 I have an MSD 5 box, using the stock distributor (points) as the actuator. Again, tach reads fine. The tach kit I got from Brothers for the C20 had a defective tach when I received it...sent it back and all is well now. I thought I needed an MSD tach adapter to fix the problem so I ordered one and now have it.

Scoyote....if you want to try the tach adapter to see if it will help/correct your problem, PM me and I will let you borrow it to try. Let me know....

[scoyote]

Wow, that is a very nice offer.
PM sent.

[ksbrktracer]

I'm no expert by any means , but I dont think a tach filter and tach adaptor are the same thing. I know on my monte ss the tach filter on it was defective (tach inop) and i bought a new one from chevrolet and it worked perfect, it looked like a points condensor with a wire out of each end and plugged into the dist and the other end hooked to the tach wire.

I put an hei in my 71 and the tach didnt work properly (inaccurate) so I disconnected it. It worked perfect with the points dist. This was before I knew about the tach filters . I also had a brand new nos printed circuit board on mine at that time.

[Lemield]

Originally Posted by ksbrktracer

I'm no expert by any means , but I dont think a tach filter and tach adaptor are the same thing. I know on my monte ss the tach filter on it was defective (tach inop) and i bought a new one from chevrolet and it worked perfect, it looked like a points condensor with a wire out of each end and plugged into the dist and the other end hooked to the tach wire.

I put an hei in my 71 and the tach didnt work properly (inaccurate) so I disconnected it. It worked perfect with the points dist. This was before I knew about the tach filters . I also had a brand new nos printed circuit board on mine at that time.

Wow...good info....Thanks...I just got this thing sitting around...figured what the heck, might as well offer it to Scoyote to try...

[Lemield]

Scoyote...I'm shipping the tach adapter to you this afternoon.