Tach Conversion - Mechanical to Electric
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From: Lenoir City Tennessee
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St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15
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.
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.
Former Vendor
Joined: Aug 2006
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
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
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
Last edited by Willcox Corvette; Jun 3, 2009 at 11:00 PM.
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From: Forked River NJ
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.
Burning Brakes
Joined: Aug 2007
Posts: 1,173
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From: Liberty Missouri
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 obtain 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
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 obtain 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 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.
Pro
Joined: Mar 2007
Posts: 738
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From: Fallbrook CA
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
Melting Slicks
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From: Lubbock Texas
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From: Paducah KY
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St. Jude Donor '03
I sent mine to Roger at Corvette Instruments for conversion. He also refaced my speedometer for me. Does nice work.
Dave
Dave
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Thread Starter
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Joined: Feb 1999
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From: Lenoir City Tennessee
Ci 6, 8 & 10 Veteran
St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15
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. 
Thread Starter
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Joined: Feb 1999
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From: Lenoir City Tennessee
Ci 6, 8 & 10 Veteran
St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15
Thread Starter
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From: Lenoir City Tennessee
Ci 6, 8 & 10 Veteran
St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15
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.
Mechanical
Electric
Just for kicks, here is the date code or whatever on the rear of the 70 face.
Electric coming apart.
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.
Mechanical
Electric
Just for kicks, here is the date code or whatever on the rear of the 70 face.
Electric coming apart.
Last edited by Eddie 70; Apr 14, 2009 at 08:12 PM.
Thread Starter
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From: Lenoir City Tennessee
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St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15
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.
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.
Here is the circuit board.
Going back together
And all back together minus needle.
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.
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.
Here is the circuit board.
Going back together
And all back together minus needle.
Thread Starter
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Joined: Feb 1999
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From: Lenoir City Tennessee
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St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15
Former Vendor
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
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.
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.
Thread Starter
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From: Lenoir City Tennessee
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St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15
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.
Thread Starter
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From: Lenoir City Tennessee
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St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15
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.
ITS ALIVE!!
I am well pleased with how it has went. Now to get it all back in the dash and working.