Tach Conversion - Mechanical to Electric
 

Since my oil pressure gauge conversion finally made it through, I thought I would try and jump to my next project in the conversion. I want to take my stock tach and make it work with the LS conversion. Since my mechanical tach now has no input, we have to give up the mechanical guts and put in some electrics. I have read at some point that someone took the guts out of a 77 or so tach and put them behind the earlier face and made this work.

Does anyone have any idea of who may have done this or how to accomplish this conversion? I don't have a tach yet but I am ready to get on with it. Any help or pointers would be greatly appreciated. I did see it mentioned in the LS thread. The poster said to do a search for the conversion, I did and found 0. I am all ears. :bigears

Eddie,

Boy, you are going all digital. . . I've been buried the past few weeks so I've not been much help. Norm was off on a medical leave and I subsituted for him. Sorry I did not get a chance to respond to your other post before you got this fixed.

You can use the 1975-1977 style tach. Best if you find a 75-76 tach since the face is closer. Once obtained this, go to my site and look up the tach board. The picture there will show you where to place the wires to power up the tachometer.

The 75-77 tach will bolt right up to your dash with out any problems. This really is an easy conversion for you. . .

Willcox

I had my tach converted to electrical. I used my 72 face and they installed the guts from an electrical tach. Most any gauge rebuilder can do this for you. Mine works much better than the old mech drive tach.

:iagree:
I did this conversion using a 75 tach. It should be pretty simple for you after all the other things you have done. You can swap the faces if you want I think there are only two rivets holding the face on after you remove the needle.

Hey Eddie....Once you install the newer tach, put in a SCI-8 from Dakota Digital. This will convert the LS tach signal to your 8 cylinder tach. The LS electronics outputs like it's a 4 banger for some reason. I'm still working on mine...gp

:iagree:

Previous owner did this to my '73 and it worked out great.

DC

D and M restoration can do this for you.
D and M

I sent mine to Roger at Corvette Instruments for conversion. He also refaced my speedometer for me. Does nice work.

Dave

I think Roger did the instruments on the Roman Chariots....

:lol::thumbs:

I got my tach yesterday to start my conversion. I will post some pics later tonight of my conversion. If I have time I may try to check its operation also. :thumbs:

Good luck with it….Get that thing going so I can see it at the grand run this weekend!!!:flag:

I have Friday scheduled off from work and I plan on being up there. Either in the Z06 or maybe the 70. :thumbs:

you have a PM:thumbs:

Okay, I have run into my first road block with the conversion. The distance between the mounting tabs on the mechanical mechanism and the electric mechanism is different.

The mechanical tach is 1 3/8 inch between mounting posts.
The electric tach is 1 5/8 between mounting posts.

I was thinking of a couple of ways to make the electric mechanism mount to the 70 face. Once the movement part is mounted, there will be no need for it to ever come off again. I thought about using something like JB Weld to make it stick. Silicone would be another choice in case I had to ever get back at it again.
I could also make some kind of adapter plate out of a plastic material.
I could try to make some new holes in the electric part of the gauge.
Any ideas are greatly appreciated.

If you've never had a tachometer apart here are a few pictures of what you might see.
Rear shots of both tachs.
Attachment 48179389

Mechanical
http://img.photobucket.com/albums/v3...n/DSC01839.jpg

Electric
Attachment 48179390
Just for kicks, here is the date code or whatever on the rear of the 70 face.
Attachment 48179391

Electric coming apart.

Attachment 48179392
http://img.photobucket.com/albums/v3...n/DSC01842.jpg

Okay, it was not nearly as hard as I thought it was going to be. I took some more measurements and got my center punch out and drill out and went to work.

I center punched the electric movement in the corners just inside the factory holes. Drilled the holes with my smallest bit. I then stepped up to the next bigger size bit until I could fit the screws to mount the face in them.
Attachment 48179393
Attachment 48179394
Attachment 48179395

Once I had the holes lined up it was just put it all back together. Woo Hoo! I guess tomorrow night I will try to power it up so I can put the needle back on it correctly.
Attachment 48179396

Here is the circuit board.
http://img.photobucket.com/albums/v3...1852Medium.jpg
Going back together
Attachment 48179397
Attachment 48179398

And all back together minus needle.
http://img.photobucket.com/albums/v3...1857Medium.jpg

nice Eddie!

Thanks, I just hope it works for me.
Attachment 48179403

Eddie,

Just don't forget to zero out the tach needle. Easy to do: Just sit the needle on the tach without pushing downward. Apply 12 volts and a ground only! The tach will go to zero.

With the needle just sitting on the spindle you can gently tap it toward zero and watch where it settles. If it is on zero push it on, if it is not tap it again and let it settle. As long as the tach is missing signal it will come to a rest at zero. It may take you a few tries but once you have it you are ready to go.

Willcox.

Thank you Willcox. I was thinking this might be the way to get it to zero since it is basically the same motor that drives all the other gauges. Back to the basement and gonna set it needle to zero. :thumbs:

Just came up from connecting the LS tach output to the tach. Hit the key and the car started. The tach jumped up like I wanted to see.

ITS ALIVE!!

I am well pleased with how it has went. Now to get it all back in the dash and working.