TACH HELP

[Nobody Cares]

I put a new tach filter on the 80 vette. No help , still not working. Question is , has anyone taken there tach out for the circuit board replacement?? What kind of project is it too replace the circuit board ?? Is there anything else i can check that might be causing the tach not to work. Fuses , wires ect ect . Thnx Dave

 

[KANE]

Well... could be a couple of things.

I'd look at these three things next:
1.) Harness from the HEI to the dash-
You'd want to rule out the signal from the HEI to the dash. This is the first step in the process of elimination.

2.) Printed circuit board on the back of the cluster-
Supposing the signal is okay, it may be in the transition from the harness to the tachometer. Check this next.

- approximately $100 to replace (image is from Eckler's)

3.) Green circuit board on the tach itself-
Assuming the first two are okay, then you may have a bad tach circuit board.

- approximately $60 to replace (image is from Eckler's)

Usually, it is one of the circuit boards that goes out. Most often, if the dash has power- it is the tach's circuit board. When the tach went out on my 1978- it was the tach circuit board.

 

[Nobody Cares]

Ok Thnx. I did check across the tach filter and it gave a reading of 15,000 ohm's. So tach filter is good. How much of a project is it too change out the tach curcuit board ?? Dave

 

[76okievette]

On my 76 its a dash removal which is not hard but you have to remove lots of stuff and the potential is there to mess up something else. Its also possible to break on of the dash pieces when removing them such as the dash pad, its a real tight fit getting it in and out. I am just saving up a few things like the clock conversion to quatz and the tack circuit board so I can get it all done with only one dash removal.

 

[Nobody Cares]

Thats sounds like a plan Okievette . Thnx Dave

 

[Art Jett]

As 760kievette said it's straightforward. Just be careful pulling your dash apart, it's old like me and breaks easily. I changed my tach circuit board and converted my clock to quartz and both work great. Art

 

[Nobody Cares]

Thnx Art Jett. I'll really be careful when gettin into the project. By the way , how much of a project is changing out the tach board. Time Wise. Do i need the biggest part of a day ?? Dave

 

[Art Jett]

Once you have the tach out it's not much of a job at all. If I remember correcly, after the board is installed you have to hook it up to 12 volts and then put the needle on at zero. I might be wrong, but I remember something like that.

 

[Nobody Cares]

Art jett Thnx. Should be ready to tackle the project soon. Thnx Again Dave

 

[Dave L.]

Are you using the stock ignition coil or a high voltage after market type?

 

[Nobody Cares]

Stock Ign. coil. Dave

 

[Dave L.]

The reason I asked was the high performance aftermarket coils cause voltage spikes and erratic tach readings.

 

[Art Jett]

I've got an MSD high voltage coil and so far it hasn't caused any problem with the tach. I'll wait and see. Hope not!