How to fix 66 Cuda Tach?

[Kevin74]

I’m working on a 66 Cuda, where the tach sending unit is remote, behind the drivers kick panel.
I started my debug adventure with a new RTE sending unit. The sending unit works great, it’s output voltage increases with engine RPM, but the tach is still dead.
So now I removed the tach from the dash, and tried applying a 1.5V battery across the two tach terminals, but still no needle movement.
Just wondering if anyone has experience with opening the guts of the tach? I see that Classic Industries has new tachs for $250, but it would be nice to fix the old one

 

[4spdragtop]

Mrheaterbox.com can upgrade the internals on it or you can buy a new board from them and install yourself

 

[Kevin74]

Mrheaterbox.com can upgrade the internals on it or you can buy a new board from them and install yourself

That’s a great website that I’m glad to have learned about. I sent them an email, and I’ll report back with their reply.
Thanks!

 

[67Dart273]

I’m working on a 66 Cuda, where the tach sending unit is remote, behind the drivers kick panel.
I started my debug adventure with a new RTE sending unit. The sending unit works great, it’s output voltage increases with engine RPM, but the tach is still dead.
So now I removed the tach from the dash, and tried applying a 1.5V battery across the two tach terminals, but still no needle movement.
Just wondering if anyone has experience with opening the guts of the tach? I see that Classic Industries has new tachs for $250, but it would be nice to fix the old one

Never do this, but now that you have, sounds like the tach meter is dead. For fun you might try your ohmeter across the two same terminals. It's possible you burned out the meter, or that it was already open or otherwise "problem"

 

[67fish383S]

Mrheaterbox.com can upgrade the internals on it or you can buy a new board from them and install yourself

They rebuilt/restored a couple of '67 speedometers for me and did really nice work. It is a bit of a pain shipping-wise because they are in Canada, but very affordable otherwise.

 

[4spdragtop]

They are only a couple hours east of me. I believe they are in Harrow.

That’s a great website that I’m glad to have learned about. I sent them an email, and I’ll report back with their reply.
Thanks!

They rebuilt/restored a couple of '67 speedometers for me and did really nice work. It is a bit of a pain shipping-wise because they are in Canada, but very affordable otherwise.

 

[Kevin74]

They are only a couple hours east of me. I believe they are in Harrow.

Here is an email reply from them with some juicy technical details. I can’t wait to open the tach to see what I discover:


Hi Kevin

What you can do is at least take the tach apart to determine what is wrong. The heart of the mechanism the meter coil hoop attached to part that moves with the pointer. the meter coil gets it connection through the clock springs front and back of the movement. You can measure the resistance of the meter coil with a multimeter on ohms at the two tabs where the internal wires attach to the clock spring adjusters. You should see something around 160 ohms give or take about 20 ohms. (it varies from tach to tach) If you are getting a resistance reading of something much lower or higher than that target of 160 ohms the meter coil is likely defective and you will have to send me the tach to have the internals replaced from another tach.

the only other parts of the inside of the tach between the meter coil and the terminals on the back is just some old fashioned resistors and diodes and wires joining the them from the front to the back. the resistors and diodes can be bypassed to test the tach as they are not really necessary with the new sending unit. run new wires front to back keeping the path the same orientation as polarity is important for which wire gets power (yellow) and which terminal is ground (black).

If that doesn't work than tach internals have to be replaced. which I would have to do, If you want to do that please send me the sending unit too so I can calibrate it as a complete system.

Brian Ball
4126 Henderson Rd.
Harrowsmith, ON
K0H 1V0
613-532-2587