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78 Camaro tachometer questions

 
TroyVan
I love my Chevy Chevette!
Posts: 5
Joined: 10/12
Posted: 10/27/12 07:21 AM

I have a 1978 Camaro Z28 that I have been doing some basic upgrades or repairs for mechanical or cosmetic reasons.  I rebuilt my cluster and had came across a deal on another cluster to use for parts.  Between my original and the cluster I got I figured I would put the best working/looking one I could.  As I was putting the new one together I decided to use the tach off the 2nd cluster but did so without knowing if it worked or not - I was told it did but it sure looked far better.

My problem is this tach does work but it seems to be high on the RPM side - 4-6K and when the car is shut off the needle drifts up to about 15K and sits there until the car is started again where my original would drop to zero when I shut the car off.

1.  Is the needle drifting ok or a sign of a problem?
2.  How can I verify the tach is accurate or calibrate it?  

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redneckjoe69
I mow my lawn and find Chevys
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Joined: 03/10
Posted: 10/27/12 10:05 AM

kinda sounds like some wires are backwards?     is the tach for a v-8 motor?     is there any adjustment on the back of the tach like aftermarket ones, 4, 6, &8 cylinder?  

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pepsi1
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Posted: 10/27/12 08:29 PM

TroyVan Welcome to CHP.

  I have a 1979 and a 1981 Z28. Now either I missed something in the translation of the K. Your saying the Tack reads 4to6 K high. Thats 4,000 to 6,000 RPM higher, correct? Then when it sits it goes to 15,000 RPM higher. Just so I'm on the same page. You are talking about the original cluster Tach? Please correct me if I'm wrong.(I'm an old Gear-Head)...LOL...Just ask Joe...
  I know you can pick the tach circut directly off the distributor cap. Like Joe said if there is a switching device for 4,6,or 8 cylinder that could be the problem. Even with a factory Tach. Somewhere in the tach circut there has to be a resistor stepping the input up or down in the Tach. circut.
  Do you have a service manual for that instrument cluster...compair your cluster versus the one you aquired. See if there is anything that looks different, in the Tach circut. Or try this just run a light gauge wire from the tach. pick-up in the Dist./Cap to the tach in the cluster. See which one acts accordingly,to what you need. I wouldn't start the engine maybe just cycle the key, to test each circut.

Bob  

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TroyVan
I love my Chevy Chevette!
Posts: 5
Joined: 10/12
Posted: 10/28/12 07:45 AM

Let me clarify, I know things get lost in translation when typing.  The 4-6K increase is what I noticed after I changed to the to the new tach from the old, which are both OEM.  There is very little room for error when installing these, just a few nuts on the OEM printed circuit on the back of the cluster,

As for the going to 15k, that is when I shut the car off the needle drifts up to there ands sits, where the other goes to zero and sits.  

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68scott385
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Posts: 1994
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Posted: 10/28/12 10:10 AM

SOS, different day  
68scott385 68scott385 68scott385

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68scott385
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Posted: 10/28/12 10:11 AM

I never saw a Chevy factory tach that read 15,000rpm.  
68scott385 68scott385 68scott385

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waynep71222
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Posted: 10/28/12 10:14 AM

what"s going on here for one thing... is the confusion of what you are typing..

when you typed just above.. going to 15K when i shut off the car... should be 1500... 15K is 15,000... but i and most of us understand you...

so your 4 to 6 K increase is actually in hundreds of RPMs instead of thousands..

~~~~~~~~~~~~~~~~~~~~~~~~~~



i have seen both types of tachometers...

ones that rest at ZERO when the key is off...

and

ones that rest above ZERO.. when the key is off..   both are normal...

~~~~~~~~~~~~~~~~~~~~~~~~~~

verifying TACH readings.... that is going to take either a automotive multimeter with an RPM  inductive clamp... some more expensive timing lights also have Tachometers built in..

Image 13487


there are also version of hand held digital tachometers... usually needing some kind of reflective surface to be applied for the unit to keep track of RPMs...

Image 16438


move slider to the side to see the hand held tachometer..  

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68scott385
I mow my lawn and find Chevys
Posts: 1994
Joined: 10/09
Posted: 10/28/12 10:42 AM

On the 1st post I give the benefit of the doubt. On the second post with same information I become doubtful, then I assume NOTHING.  
68scott385 68scott385 68scott385

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pepsi1
I mow my lawn and find Chevys
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Joined: 09/11
Posted: 10/28/12 01:59 PM

Icon QuoteTroyVan:
Let me clarify, I know things get lost in translation when typing.  The 4-6K increase is what I noticed after I changed to the to the new tach from the old, which are both OEM.  There is very little room for error when installing these, just a few nuts on the OEM printed circuit on the back of the cluster,

As for the going to 15k, that is when I shut the car off the needle drifts up to there ands sits, where the other goes to zero and sits.


TroyVan

Wayne and I know what your trying to say. So either follow Wayne's way of thinking or mine. I have seen aftermarket Tachs with 12,000RPM tell tales Okay.

Like I said there is a Tach lead that comes off the Distributor Cap. In fact it is marked as such. If you can tap into that connector I'm sure you will find your problem. All the Newer VOM's have connections for reading just about any input you give it... Grin  Cool

Bob  

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TroyVan
I love my Chevy Chevette!
Posts: 5
Joined: 10/12
Posted: 10/28/12 02:27 PM

sorry forgot the period I meant 1.5k.  

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