How to restore the original '71 vette's tachometer

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danielepiacenza

Well-known member
Joined
May 28, 2010
Messages
61
Hi guys,
I'm at work on the interior of my '71. The probles is about the instument, gauge and radio (all, haha).

About the speedometer the problem is not in the instrument, but on the ring in the Muncie ... no problem, I will have only to change.

About the radio, I would like to replace the modern Alpine I have with the original stock, but with a little "alternative" source by a little amplifer and Ipod. All not invasive, but hidden (see the pictures)

About the tachomet I have serius problems. It don't work. The wirw is ok and turn good but the instumes make a little noise and the arrow don't move. I open it and I find a "bridge with magnets" dirctly connect to the wirw. It turn in a "buket" and this buket is just inside the case cover of the instument. (here is the pic:
http://picasaweb.google.com/lh/photo/NCLp18HsTVXqKipQWEPdDg?feat=directlink
http://picasaweb.google.com/lh/photo/ttyH3oce6NjQWFuJa6_9Iw?feat=directlink
http://picasaweb.google.com/lh/photo/BQ5sWrqMeFOb7JpKBTnpyQ?feat=directlink
http://picasaweb.google.com/lh/photo/uVaSxvOY1tQnqXDXtVprgA?feat=directlink
http://picasaweb.google.com/lh/photo/Fy5B-FmYqH737oO-B4iqMA?feat=directlink
http://picasaweb.google.com/lh/photo/oiM6P3w_18zvOBJV7hJH-A?feat=directlink )

How can I repair my tachometer. In your opinion is a good idea to buy a not new tachometer on ebay and replace only the core?

Thanks to all and apologized me for my bad english. Who have time, can take a look to my work of today here, there is also the modified to the cigarette basket for apply the Ipod.

Happy new year to all!!

http://picasaweb.google.com/dani.cellulare/RimozionePlancia?feat=directlink
 
IMO, find a electronic tach from 75-77 vette and be done with it....

those old mechanical things were a headache from day one when new....

they got more fixes out than drug addicts.....the patient still seems do die....

:cussing::quote:
 
Tanks Gene,
but is possible to instal and fit correct an electric tachometer? The shape is the same like the original? Finally, how. can I fit it?
 
danielepiacenza said:
Tanks Gene,
but is possible to instal and fit correct an electric tachometer? The shape is the same like the original? Finally, how. can I fit it?
Click to expand...

The mechanics of the tach faces are a direct change out, the lettering is slightly different, but the RPM count/deflection/angles are the same....there maybe a slight difference in the yellow/orange and red markings on the scales....

but over all appearance is fine, take a pretty good sharp eye to tell the differences I assume NCRS in not on your side of the pond.....

I went for a white vinyl faced overlay on my speedo tach assy to match up with the new gauges in the center...not really great looking, but it's close enough....

the wiring is simple....ignition hot to tach, ground, and then the dist tach pulse off the points or HEI tach wire, through a tach filter....which I can send a schematic for, an you can get parts on your side to build one....not OEM, but one HELL of a lot cheeper.....

back when, I traded my points/tach drive dizzy that was all destroyed for the electronic tach with a vette shop owner in Maryland.....I made out like a bandit, IMO....

;):bump:
 
I have an electric tach out of a 76 in my 74 Vette. The lettering of the face is a little different. I hope to send it in and have it refaced sometime in the distant future so it will match. Install is easy. It is a direct bolt in then you just need to run three wires. Positve, Negitive, and signal just like any other tach.

Now if you really want to keep your mechanical tach I have a one out of my 73 parts car I would sell for a reasonable offer plus shipping.
 
You can put the '71 faceplate onto 75-77 "guts". The sweep is the same. I did this on my '71 many years ago and it works great & looks factory (71 had green letters, 72-up white).
 
zwede said:
You can put the '71 faceplate onto 75-77 "guts". The sweep is the same. I did this on my '71 many years ago and it works great & looks factory (71 had green letters, 72-up white).
Click to expand...

There are 2 screw holes, one on each side of the needle center...but the electronic is wider than the mechanical....how did you solve that problem??



:clobbered::goodevil:
 
The difference is minor, so I slotted the holes. It's not noticable when installed. If you look closely you can see a tiny gap on one side of the screw head but no one has ever noticed without being told what to look for.
 
My 70 has a mechanical tach and speedo. As far as I know they both work fine. However, they're 40 years old. I'd like to "0" time them and return to all new. There are people who will renew these units. They advertise in the NCRS (National Corvette Restoration Society) Restorer magazine. I remember seeing their prices and forget the details but they are expensive if you want to replace the mechanism with a new mechanism since there aren't any being made anymore. They will also renew faces. Maybe someone who has had their units renewed can supply better detail. I can look up names, addresses, email addresses of tach/speedo restorers if you wish.
 
ONE thing to keep in mind, and that is, the accuracy of any tables to do with tire diameter and ratios in diffy's/trannies is to engine speed....are NOT to be trusted above 80 mph.....

I got it shoved but good from Turtlevette some years ago on that one, according to the TABLES and shit, I was doing some 150 mph.....and so he was proven right, I bought a GARMIN GPS.....THAT I believe, screw all else....

tach is 5% high at 6000 rpm, proven myself, electronically, CASE CLOSED....

tach gains that 300 rpm starting around 3k rpm making it 10% high....same on up across the board.....

dead nutz on accurate at idle to 2000 rpm.....I dunno why, just IS....dead stock '75-77 tach....

my speedo was set with the correct gear for speedo to read what tach said at X speed.....

but GPS said it was 10% over indicating....across the board....changed the driven gear in the tranny....now GPS and speedo agree up to 80 mph....

80 is really 78mph....fine so what....
lower is dead nutz on.....the way God intended....

100 indicated is only 94 mph....SO both stock tach and stock speedo are NOT linear in their readouts....

so NOT to trust your instrumentation.....


:crap::clobbered::clobbered::banned:
 
Gene: Funny, I found the exact same thing on the 75-77 tachs years ago. I built a square wave generator and checked the frequency with a scope. I ended up moving the needle a bit so it reads a little low at low rpm (to minimize the error at high rpm).
 
zwede said:
Gene: Funny, I found the exact same thing on the 75-77 tachs years ago. I built a square wave generator and checked the frequency with a scope. I ended up moving the needle a bit so it reads a little low at low rpm (to minimize the error at high rpm).
Click to expand...

Zwede, you laugh at my setup....really OLDE Tek 453 scope....a digital audio osc from early 80's yet....line synch the scope....confirm the rep rates, feed into a old horizontal output transistor from color TV sets of ages ago....TO3 case....turn on the ignition, connect the transistor collector to the tach output, ground the emitter, feed the audio in... drive transistor into saturation, leave the GM module in the circuit for the damping characteristics....

read tach....compare rep rates, and keep 60 hz line synch for to verify freq and counts....done deal....

:p:flash::flash: told you I was a geek.....

:p
 
Not bad. I built a simple flip-flop circuit (2 transistors, 4 resistors, 2 caps) on a bread board, fed the output to a power transistor. Verified frequency with ancient Tectronix 465 scope.

Whatever gets the job done.
 
zwede said:
Not bad. I built a simple flip-flop circuit (2 transistors, 4 resistors, 2 caps) on a bread board, fed the output to a power transistor. Verified frequency with ancient Tectronix 465 scope.

Whatever gets the job done.
Click to expand...

Nanner nanner nanner, my scope older than yours.......I used to spend many a daze looking at a 465 lab scope with a EE over my shoulder.....

then the company owner walk in, and have the trace all over the joint and GAWN forever....walk away disgusted, muttering 'damn scope'.....

seriously.....the man was a PHD EE to boot, but he treated me VERY well....

loved that company....:drink:
 
Hi guys,
I have news. My friend that have a 72 very custumized send to my his old tachometer. I replace the case and the "face" with my and use only the core.

In the beginnig the instument don't work because there was a little distance betewwn the "bridge" (in the core) and the mechanism. I work on it and now it work.

The RPM are not very close to reality, but work good.

Thanks to all for the good ideas.

I'm working for close all the interior now.
 
I did this on an LT1 car along time ago, not sure why but I was young. I had a 75-77 Tach that I had refaced. We had a guy by the name of Chuck B. and he claimed he was the one that started the gauge refinishing business. My gauge looked perfect when it came back and all the colors were correct for a 72. He retired and the last I heard was he sold all of his equipment to Mid America. I don't think they have done anything with it, but any of the gauge rebuilders out there should be able to do the same thing. I don't remember what he charged me, but that was in the late 80's so I am sure it has gone up allot.
Justin
 
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