Stock Tach acting up - Team Camaro Tech
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post #1 of 11 (permalink) Old Jan 31st, 09, 10:04 PM Thread Starter
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Ken
 
Join Date: Oct 2007
Location: St. Louis, MO
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Stock Tach acting up

Hey Guys, Nice warm day in St. Louis, let the car run for the first time in a couple months and I noticed that the tach needle won't go above a certain point regardless of engine RPM. It "looks" like it physically hits something and stops. I took the lens off and gently moved the needle up with my finger and it will go past that point, but then it does the same thing, it just stays within a higher range. I did a lot of things up behind the dash—ventilation, wiring etc., could I have knocked a wire loose or something? I also remember back during the restoration one of the screws in the faceplate had jiggled loose over the years. When I replaced it I got a fingerprint on the faceplate, and when cleaning that I accidentally snagged the needle a couple times with the cloth I was using. It kind of did the same thing, remaining in a position above where it should be. I gently pushed it back down and everything looked OK. I have driven it between then and today and I think I would have noticed if it wasn't working right at that time, but maybe I didn't notice. Anyway, not knowing the internal mechanism, did I break a spring or something internally? Has anyone run into something like this? Most importantly—can it be fixed without removing the whole stinkin' dashboard or everything behind it all over again?

How does Jim end his posts? Something about "when you believe everything is finished, that will just be the beginning."

Thanks.
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post #2 of 11 (permalink) Old Feb 1st, 09, 09:54 PM Thread Starter
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Ken
 
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Re: Stock Tach acting up

Have I posted in the wrong forum?
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post #3 of 11 (permalink) Old Feb 2nd, 09, 06:33 AM
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Dave
 
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Re: Stock Tach acting up

Unfortunately i cant help you but am interested in the answer. Mine is off about 300 rpm and hasbeen since i cleaned it 3 years ago.
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post #4 of 11 (permalink) Old Feb 2nd, 09, 08:07 AM
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Ted
 
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Re: Stock Tach acting up

Could maybe when you were cleaning, snagged the needle and stripped it. I don't know if the tach drive(where the needle fits on) has splines or just presses on. Maybe try a dab of glue on the shaft and push the needle on. Maybe the drive is spinning in the needle housing. If you have to remove it you should be able to get it out without removing the cluster.
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post #5 of 11 (permalink) Old Feb 2nd, 09, 08:12 AM
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Ted
 
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Re: Stock Tach acting up

Have you gone to HEI ignition? I have read some posts that the original tachs and HEI can cause the tach to fry. The new repo tachs don't have that problem. I think one of the moderators has a sticky on this issue.
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post #6 of 11 (permalink) Old Feb 4th, 09, 10:02 AM Thread Starter
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Ken
 
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Re: Stock Tach acting up

No HEI. Stock ignition, original tach.

Does anyone know what the internal mechanism is? Is it gears? Is it a magnet spinning around the shaft?

Is it a needle pressed onto a shaft? Although if that were the case, I think I would have bent the needle before I could have stripped it. I barely snagged it and it moved pretty easily. But it stayed up there until I pushed it back down. And then it stayed down. It does go to zero when the engine is off, it just won't go above 800 when running.
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post #7 of 11 (permalink) Old Feb 5th, 09, 09:55 PM Thread Starter
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Ken
 
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Re: Stock Tach acting up

It's called a d'arsonval meter movement, not reproduced, hard to find, expensive to fix. The Tachman said he doesn't believe I damaged it, he thinks the jewel and pivot are just finally worn out after almost 40 years. I have a hard time believing that because it gave no warning at all... but maybe he's right. Now, can I remove it without taking the whole dash or dash innards out again?
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post #8 of 11 (permalink) Old Feb 7th, 09, 08:49 AM
tachman
 
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Re: Stock Tach acting up

Quote:
Originally Posted by KenFro View Post
It's called a d'arsonval meter movement, not reproduced, hard to find, expensive to fix. The Tachman said he doesn't believe I damaged it, he thinks the jewel and pivot are just finally worn out after almost 40 years. I have a hard time believing that because it gave no warning at all... but maybe he's right. Now, can I remove it without taking the whole dash or dash innards out again?
go to www.tachman.com and click on troubleshoot and you will see 30 years of my experience of info on tachs, speedos, gauges, etc.
since it is 40 years old, and i believe this was a 69 camaro tach, it is great that it still does work. do not paint tach needles, they have to be re balanced to be made accurate again. i have factory training in this area
www.tachman.com/camaro.htm
tachman
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post #9 of 11 (permalink) Old Feb 7th, 09, 09:13 AM
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Re: Stock Tach acting up

Might need to be professionally cleaned/repaired. I had mine done several years ago and it works perfectly.

"Government is not reason; it is not eloquent; it is force. Like fire, it is a dangerous servant and a fearful master." ..... George Washington

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post #10 of 11 (permalink) Old Feb 7th, 09, 10:21 AM
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Alan
 
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Re: Stock Tach acting up

All good advice, these are precision instruments. Mine was stopping right at 12 o'clock (3500rpm). Turned out the tip of the needle was hitting the faceplate screw. Assuming yours is doing the same, if you have the delicate touch, you can GENTLY bend/tweek the tip of the tach needle, but I stress GENTLY, the needle is very very thin aluminum. If you don't want to attempt bending the needle, you could shim the guts of the gauge from the backplate so the needle clears the screw.

alan

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post #11 of 11 (permalink) Old Feb 7th, 09, 11:23 AM
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Re: Stock Tach acting up

I'm not sure how "precision" they are. If you look inside one you'll see a fair amount of "seat of the pants" engineering was involved - examples being wrapping wire around one of the pivot cross arms for counter balance, or bending a cross arm to counter balance. The bearings in a d'arsenval movement are known as jewels since precision d'arsenval movements often used ruby or saphire jewels for the bearings. These old tachs often used plastic jewels or a metal pivot point. I don't think there was much calibration involved either. If they were close they got shipped. BTW: The needle will pull straight off the movement shaft. So if you need a crude calibration adjustment, you can simply pull the needle off and relocate it. There is no need to bend anything.

Dave
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