69 tach calibration - Team Camaro Tech
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post #1 of 11 (permalink) Old Jan 26th, 10, 04:53 AM Thread Starter
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Dave
 
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69 tach calibration

I've spent alot of time digging thru the tach question archives and still dont knowthe answer. My stock 69z28 tach is off by about 350rpm which i verified with my shift light and another tach. IS it possible and is ther any adjustment potentiometer on the tach? It reads to high all the time. I dont think a filter will help as it is consistently high.
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post #2 of 11 (permalink) Old Jan 27th, 10, 06:47 PM
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Re: 69 tach calibration

I took apart a GM factory tach for my 1974 Nova a few years ago out of curiosity to see what was inside and I don't remember seeing any type of user adjustment although there may be something on yours.
I wonder if inside your tach's electronics if something is off a little bit or just within a tolerable level from when it was made ?

Here is a link to some pictures of the electronics inside mine:

http://rides.webshots.com/photo/2685...60464735uObCcJ

There could be a capacitor that has dried out, a poor connection somewhere, or even a weak return spring on the needle assembly. Looking at my old pictures there looks to be a tube with wire wrapped around some type of ferrit core and maybe this can give an adjustment to the readings of the tach.

Somewhere in my webshot photo's I show hooking up my tack to a signal generator and a power supply and I could get a relationship to the amount of pulses sent out by the signal generator and where the reading would be on the tach. Sorry I don't know more specifics as I did this years ago and can't remember it all.

Jim

1974 Spirit Of America Nova (being restored), 1973 Nova Custom, 1968 Chevy II (Garage Find 2012)

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post #3 of 11 (permalink) Old Jan 27th, 10, 07:42 PM
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Re: 69 tach calibration

My OER 68 tic toc tach has an adjustment. It's a tiny blue pot, reached thru a teency hole in the back of the tach.

This is a reproduction unit made in china in the 21st century, and a 68 not a 69... so could very well be different.





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post #4 of 11 (permalink) Old Jan 27th, 10, 09:29 PM
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Re: 69 tach calibration

I cant see up under the dash to check mine
Even so inside there will be an adjustment to correct....when tachs are made, and component where not as consistant a modern ones back then, they would have been calibrarated before the production line
All the tuning tachs I have and seen all have a calibration adjustment somewhere

My Spelling is not incorrect...it is creative

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post #5 of 11 (permalink) Old Jan 28th, 10, 05:26 AM
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Re: 69 tach calibration

Quote:
Originally Posted by Dave69Z View Post
I've spent alot of time digging thru the tach question archives and still dont knowthe answer. My stock 69z28 tach is off by about 350rpm which i verified with my shift light and another tach. IS it possible and is ther any adjustment potentiometer on the tach? It reads to high all the time. I dont think a filter will help as it is consistently high.
I have a 200 rpm error on the high side also in my 69 dash tach which I know is original. My pointer sits on 200 rpm's when the engine is off so it looks like mine can be corrected by removing the pointer and re-installing it on the zero mark. Maybe you can too. It's easy to do by removing the front bezel, but you're going to have to be very careful removing the needle. Hope this helps. I haven't done it yet, since I'm knee deep in my engine and trans.

69 SS, 350/300 h.p., M-20, 12 bolt, matching numbers.


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post #6 of 11 (permalink) Old Jan 28th, 10, 07:47 AM Thread Starter
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Re: 69 tach calibration

mine is the same as yours reelknots. But im afraid to try and remove the needle. I will probably break it.
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post #7 of 11 (permalink) Old Jan 28th, 10, 12:01 PM
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Re: 69 tach calibration

Yeah, pull the needle Dave. Maybe bend tweezers to make a gear puller. No, don't waste a good roach clip. Did I say that?

One owner 69 Camaro,(yep, bought it new
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post #8 of 11 (permalink) Old Jan 31st, 10, 09:23 AM
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Re: 69 tach calibration

on a 69 i had i pulled needle & borrowed a timing light with a built in rpm gauge.i took tack out & hooked it up under hood its easier to work with than when its sitting down in the dash.i started car once i removed needle & i used a pair of needle nose pliers bent at a 90 degree bend & be extra extra careful take your time removing needle.i put some paper towels between face & pliers so as not to scratch face of tach.once i had tach hooked up i barley set needle on pointer stem & started car.had my wife read the timing light rpms & i gently took pointer & moved it to the rpms she said it was running.if you don't push pointer all the way down when you are trying to set rpms you can move it it has splines on the pointer shaft so you don't push it all the way down till you get the needle set.my tach was a oer & not one that came with car so they may be different but I'm pretty sure they are the same.before you push pointer down on stem start engine several times & recheck rpms with light then seat the pointer on stem.if rpms is off you will have to start over.hope you get rpms right first time took me twice to do but its not hard to do.
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post #9 of 11 (permalink) Old Jan 31st, 10, 10:12 AM Thread Starter
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Dave
 
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Re: 69 tach calibration

unfortuantely my tach is originaltothe car thats why im nervous about damaging it. I may go aftermarket like theoer andsee how that works. Thenif i have to workon it, not a big deal if i damage it. I was hoping there was a way to claibrate it either with and djuster or bu adding a pull down resistor in the line.
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post #10 of 11 (permalink) Old Jan 31st, 10, 11:06 AM
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Re: 69 tach calibration

It may be possible to slip the pointer on the shaft without removing the needle. Grip the shaft with a pair of needle nose and slip it up or down scale as needed. But even this has it's risks. If the needle is stuck on there pretty good it would probably be easy to bend the pointer just by grabbing it with your fingers.

Dave
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post #11 of 11 (permalink) Old Jan 31st, 10, 12:05 PM
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Re: 69 tach calibration

I removed and recalibrated my temp gauge like above...
I made a small tool, a bit of sheet metal un a U with a slot in the bottom..this fitted underneath and supported a large area of the bottom side of the needle
That way when pulling of one doesnt bend ot twist it or damage the paint.
Put the sensor in a jug of boiling water...Known 212 F...then located the needle just on the red or orange (cant rem which think was the orange....the idiot light is 235 F so I would imagine the red on the gauge would be the same...red light Stop rule.)
Did not press all the way on just enough to hold
I then checked what each mark on the gauge read as I re heated the water with a thermometer.

My Spelling is not incorrect...it is creative

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