Dead tach....need tach filter?

I discovered another husband/wife gauge and clock repair service earlier this Spring called Redline (www.redlineg.com) in TN. Bought a used '79 Corvette tach from them on e-Bay that they tested and calibrated before shipping to me (I wanted to use the board and coil to do the conversion on one of our tachs). Maybe I'll contact John there and pose the question.

I had my tach done in April by Tach man and I thought it was all good until last night when I took the wife down to the ice cream shop for a treat. The tach started acting erratic and when we got there, then I turned off the lights and it started working normally, lights on jumped 1000rpm, turned signal on jumped all over, turned the brights on really jumped all over the place. It didn't do this when I installed it. The tach must be getting extra signal from the dash lights. I will pull the cluster out, inspect it and put it back in to reseat the plug. hopefully it will take care of it. Clanceman Let me know if tou have the same trouble.

Thanks SS tool man, as soon as i get it installed I will put it thru those same paces to make sure.

Looks like he gives a 2 year warranty in case it's his work is at fault. Hope it's a simple fix for you.

Mcarlo77 wrote:I discovered another husband/wife gauge and clock repair service earlier this Spring called Redline (www.redlineg.com) in TN.  Bought a used '79 Corvette tach from them on e-Bay that they tested and calibrated before shipping to me (I wanted to use the board and coil to do the conversion on one of our tachs).  Maybe I'll contact John there and pose the question.

I purchased the tach I used for the gas gauge conversion from them and it worked great. I wouldn't hesitate to purchase from them again.

clanceman427 wrote:Don't know the answer to that one.  We need someone here to run an experiment.

My memory is foggy but I think I had my factory 73 tach hooked up to HEI years ago and it worked fine. HEI is long gone and running MSD system. It does work with a MSD box if anyone is wondering. My tach does work but is not as responsive as a aftermarket unit. I'm running a SUN tach for that reason, easier to see also. No good if you are going after the factory look though.

I got a chuckle out of the tachman's "solid state" board. Haven't heard that term in years. I don't recall the tachs having tubes. Not tryin to sound like a smart a$$.

Gary the "Tach Man" did one for me for my 1973 el Camino SS 454 and it worked great. The price was 250.00 on mine. With shipping it to him and getting it back was about a week. I think you will be pleased in the long run.

I wanted to revisit this thread that was started a few years back. There was a lot of good info passed around which was very helpful to me. I finally acted on this earlier this winter and was on a mission to restore (repurpose) a fuel gauge as a tachometer before the end of the year. The real kick in the pants was Mitchell Murphy. Many of his parts for his Laguna restoration were burned in a fire at the paint shop that was doing the work. He sent me a moderately charred tachometer that I was tasked to test and/or repair. Fortunately the tach was functional but the appearance was rough. So I went into high gear in hopes that I could help a fellow g3 junkie in need. After months of testing, cursing, pondering and trying, I've got my first "test mule" completed. Started out as a crusty gas gauge and now is a fully functioning tachometer. Here is a couple pics of the transition. I'll be posting a detailed video on this process in the coming weeks. Hope this encourages others to tackle their own gauges. Oh, and hang in there Mitch! Yours is currently in pre-op!



BEFORE:



STRIPPED TO BARE METAL:



HOUSING PAINTED:



COMPLETED TACHOMETER:

Glad to see this thread back! Mitch is a very good friend of mine too! Would love to know how you got the tach face to look so correct!

Good to know there is options if need be. I was fortunate enoug to find a complete setup of gauges that all worked, including the original tach. I love that it works and hope it continues to do so. I am however happy that geniuses like you are abel to help others like me find a solution. Thanks for this.

a-body wrote:Glad to see this thread back! Mitch is a very good friend of mine too! Would love to know how you got the tach face to look so correct!

This has been in the works for a number of years. I've been in the printing/mailing business for a long time and had one of my vendors who does graphic design and who is also a car guy, design this gauge face. I supplied him with a tach I had in my stash for reference. There were no fonts out there that really matched this typeface that GM used, so he created it from scratch. Finally after months of going back and forth with changes and test prints we overlaid on the original tach to make sure it fit proper, we came to this final design. It's not exact, but its real close. The biggest challenge was learning a new process of laser printing on special paper so it could be transferred to a mylar film to apply to the face of this tach. This system requires several pieces of equipment to make it work properly. And some of the equipment didn't work with this method so I had to purchase another one from a different manufacturer. Then I started to get good prints that I could apply to my test board (picture below) to hone in this technique. So after many months and test print failures, I felt confident enough to apply this "overlay" print to an actual gauge, which is the one pictured in my earlier post. This took several weeks of brainstorming to figure out how to apply this overlay print to this recessed "canvas" or face of the gauge and have it aligned properly. This first test went well as it appears centered on this test piece. The other process I used was airbrushing. So everything white is toner based printing with a white "foil" applied on top of it. Then all the color was airbrushed with stencils I had made. All in, I have well over $1k invested in this with graphic design, equipment, materials, parts, paint, not to mention many hours of my time. But I really feel it was well worth it. After I complete Mitch's tach, I'm refacing the tach for my 75 Grand Am and then creating a 160 MPH speedo for my Laguna using the guts from a 68 firebird speedo. I'll document these gauges in a video to help out others who want to tackle this process on their own.

TEST BOARD:


BACK OF TACH WITH NEW CIRCUIT BOARD:

First off, WOW. Impressive.  

g3chevy / Mr Pontiac wrote:There were no fonts out there that really matched this typeface that GM used, so he created it from scratch.

From the looks of the font style, it appears to be for 1975-1977. '73-'74 looks slightly different still; see for yourself…


I would like to refresh the face of the tach in my '74 Monte Carlo but I can't justify the $1,000.00+ to do so. Nevertheless, really nice job and nicely executed.

You can buy a decal kit from a Seller named customgauges on e-Bay for the '73/'74 style tach.  Bought several kits from them when refurbishing G3 tachs and they look nice.  The initial kit you purchase for $27.99 is shown with white background, but they have an add-on option to change that to black by making a separate purchase at the same time for an additional $30.  Thinking of buying another kit after finding a '73 tach that could use a facelift. Here are the two e-Bay links you'll need.  Good idea to contact them ahead of time to make sure they draw the connection to produce the decal kit in black.

https://www.ebay.com/itm/380474491511

https://www.ebay.com/itm/381476840671

Nice work G3!!!

....... that looks good.

All your time to "figure" it out. YES , ITS WORTH IT.

Mark

zucchi wrote:First off, WOW. Impressive.  

g3chevy / Mr Pontiac wrote:There were no fonts out there that really matched this typeface that GM used, so he created it from scratch.

From the looks of the font style, it appears to be for 1975-1977. '73-'74 looks slightly different still; see for yourself…


I would like to refresh the face of the tach in my '74 Monte Carlo but I can't justify the $1,000.00+ to do so. Nevertheless, really nice job and nicely executed.

Thanks Zucchi! Yes, the 73-74 tachs used a different typeface and also a different circuit board that was talked about further back in this thread (so much good info in this old thread). I believe the aftermarket circuit board I used on this 75 tach will work on yours as well since it has provisions for a 4 post tach. Depending on how Mitch's tach turns out, I may provide this as a service to recoup some of my costs. If you could have someone design a graphic for the 73-74 style tach, it would save you about $200 on my side. Then all I would have to do is reface the tach and it'll look brand new. What would a fair price be for this type of service?

impalamonte wrote:Nice work G3!!!

....... that looks good.

All your time to "figure" it out. YES , ITS WORTH IT.

Mark

Thanks Mark! I love figuring out stuff that benefits our hobby...or should I say sickness lol.

Btw, your Monte turned out amazing! You gotta love that LS power!

So I finally read through this entire thread.

One thing that was missing throughout was that nobody mentioned if they referenced the wiring diagrams in the service manuals.

This may or may not be helpful but I'll share my tach/gauges upgrade story.

My '74 Monte Carlo came from the factory with HEI (it was built in August of 1974) and idiot lights; no gauges, no tach. Back about 1985, I pulled a gauge cluster from a '73 or '74 Monte Carlo in a wrecking yard. I then went to a '75+ GM to harvest the HEI tach wiring harness; could've been a Monte Carlo, could've been a Firebird… That harness looked like the one shown earlier in this thread…

Mcarlo77 wrote:

Studying the wiring diagrams, I knew I had to make some changes to the instrument cluster connector; I needed to add one terminal — which I also harvested from the same car I got the gauges out of — to the connector for the tach and I needed to move two — i think — of the terminals to different positions. After I made the changes to the connector, I installed the "new" gauge cluster into the dash and it worked like it's supposed to. 38 years later, it's still working fine — knock on wood.

If it would be helpful, I could post photos of the wiring diagram for 1974 and 1975 Chevrolet.

I figured I would post a video of how my tach behaves…



While I was at it, here are the wiring diagrams for 1974 and 1975 Chevelle based cars.
1974 wiring diagram
1975 wiring diagram

Looking over the diagrams, I reminded myself that I had to switch around a lot more terminals than I remember.

The main take away from this is the idiot light to gauges swap is easier when you follow the wiring diagram.

Hope this helps.

g3chevy - Nice work!! The gauge looks great.

My gas gauge tach is still working good. One of the best mods I've done.

Mcarlo77 wrote:You can buy a decal kit from a Seller named customgauges on e-Bay for the '73/'74 style tach.  Bought several kits from them when refurbishing G3 tachs and they look nice.  The initial kit you purchase for $27.99 is shown with white background, but they have an add-on option to change that to black by making a separate purchase at the same time for an additional $30.  Thinking of buying another kit after finding a '73 tach that could use a facelift.  Here are the two e-Bay links you'll need.  Good idea to contact them ahead of time to make sure they draw the connection to produce the decal kit in black.

https://www.ebay.com/itm/380474491511

https://www.ebay.com/itm/381476840671

I bought my gauge faces from them. When I bought them they used to be known by White Face Gauges. I guess they needed a new name to branch out from just white gauge faces. Prices are a little cheaper on their website as well.

http://www.whitegauges.net/categories/Chevrolet/Malibu/1973%252d1977/

I think their e-Bay Username is just that and White Gauges is their official company name. And actually, it is a dollar cheaper to buy on e-Bay due to shipping charges applied on their website. Strange as they would be paying e-Bay fees. Anyway, as mentioned, it is a nice decal kit.

Hawk03 wrote:g3chevy - Nice work!! The gauge looks great.

My gas gauge tach is still working good. One of the best mods I've done.

Mcarlo77 wrote:You can buy a decal kit from a Seller named customgauges on e-Bay for the '73/'74 style tach.  Bought several kits from them when refurbishing G3 tachs and they look nice.  The initial kit you purchase for $27.99 is shown with white background, but they have an add-on option to change that to black by making a separate purchase at the same time for an additional $30.  Thinking of buying another kit after finding a '73 tach that could use a facelift.  Here are the two e-Bay links you'll need.  Good idea to contact them ahead of time to make sure they draw the connection to produce the decal kit in black.

https://www.ebay.com/itm/380474491511

https://www.ebay.com/itm/381476840671

I bought my gauge faces from them. When I bought them they used to be known by White Face Gauges. I guess they needed a new name to branch out from just white gauge faces. Prices are a little cheaper on their website as well.

http://www.whitegauges.net/categories/Chevrolet/Malibu/1973%252d1977/

Thanks Hawk! You definitely helped pave the way with your tach build. Hats off to you for blazing that trail!

Okay, just completed another tach restoration for Mitch Murphy. I posted a new thread with the details. But I wanted to update this thread due to new information I received from one of the manufacturers of these new tach circuit boards I've tested in the past and most recently a couple weeks back. All the testing I did with known good original GM circuit boards worked flawlessly utilizing the original tach filter that goes inline from the tach lead on the HEI distributor to the gauge cluster itself. Then I tested 2 new circuit boards on these working tachs and got almost no movement of the needle or very erratic movement of the needle. Tested on 2 different vehicles with the same exact results. Then on a whim, I decided to bypass the tach filter and the sun broke through the clouds and all was well again. Both aftermarket tach circuit boards worked perfectly. That's when I spoke with one of the manufacturer directly. They said they were not aware of any issues with using tach filters with their boards. Then I asked "do you test them on your side with a filter?" And they said they do not use a filter when testing any of their boards. And then I asked if there was a risk of running without one and they said no. They have a lifetime guarantee on their boards and he said if it quits working, send it back and they'll send out a new one. Good enough for me. So far so good.

The info from Wilcox falls in line with what I was told by Ron @ Redline Gauge regarding the use of a tach filter. He told me that they were not needed and went so far as to say they were actually detrimental to the point where they would eventually fry the circuit boards. In his words..."GM's way of making money in the shops replacing them".

Mcarlo77 wrote:The info from Wilcox falls in line with what I was told by Ron @ Redline Gauge regarding the use of a tach filter.  He told me that they were not needed and went so far as to say they were actually detrimental to the point where they would eventually fry the circuit boards.  In his words..."GM's way of making money in the shops replacing them".

Good to know! Thanks for sharing this info Mcarlo77!

“fack”. I believe that is misspelled. To kind of work with what g3chevy described above, I believe that you saw a deflection in the tach needle due to the input from your HEI. Chances are that this was all it was, I/E, not an actual correct reading of the engine rpm. It would be nice to see the back of your tach when you remove it. Whatever it was that you possibly burned out or opened up might be fixable. If you can solder something back together, then you could try a filter.

REVINKEVIN / Mr. 600+HP wrote:“fack”. I believe that is misspelled. To kind of work with what g3chevy described above, I believe that you saw a deflection in the tach needle due to the input from your HEI. Chances are that this was all it was, I/E, not an actual correct reading of the engine rpm. It would be nice to see the back of your tach when you remove it. Whatever it was that you possibly burned out or opened up might be fixable. If you can solder something back together, then you could try a filter.

Not sure I follow you Mr. Revin. All the tests I did were in conjunction with my timing light showing the actual RPMs at the time of the test. So with the filter, only the factory GM circuit boards would work and not the new circuit boards. Then I removed the filter and both new circuit boards worked correctly.