Tach reading too high

[doubleyellow]

My original Rallye gauge tach is reading about 2 times too high. Set the idle RPM to about 850 (using 30 year old Sun meter) and the dash tach is showing about 1400.

Any suggestions would be appreciated.

 

[Chryco Psycho]

Convert it to modern electronics , the company that makes the kit eludes me right now

 

[Challenger RTA]

Convert it to modern electronics , the company that makes the kit eludes me right now

MOPAR Products

Real Time Engineering

Tachometer Repair Restoration for Chrysler Classic Cars

E-body Rallye Instrument Panel Restoration Service Dash

www.performancecargraphics.com

 

[moparleo]

Also requires calibration after the conversion.

 

[6PKRTSE]

My tach reads high also. At 45 MPH it reads about 3600. It should be around 2400.

 

[doubleyellow]

Thanks Guys, I could convert to new electronics, but concerned I would mess up my original Tach face. I’m just cruising with it so I’ll just live with it. Guess its better it reads too high than too low !!

 

[Shaker71]

The tach is just reading a square wave from your ignition. And converting it to voltage to drive your tach needle.
Hook it up to a signal generator you can test the tach. The other side of the equation would be to hook an oscilloscope to the negative terminal of your coil and see the pattern and frequency. That would be the same as your Sun meter reading it, except with the Sun meter you don’t see the pattern. Since your Sun meter is reading correctly there’s a component issue in your tach. An older capacitor that’s leaking voltage?
Here’s a circuit diagram.
If you had a complete failure if, let’s say, the leads were reversed would blow the 1N914 Diode. I’d guess your C1 or C2 capacitor is going out on you. Maybe your R1 resistor has gone of spec. Capacitors are usually the culprit.

 

[Rons340]

I rebuilt mine myself but did have to recalibrate it. I am including a link below provided by the vendor for the entire process. The calibration instructions start on page 3 of the information. Since yours is working that should be all it needs.

New Exact Reproduction OEM-Style Mopar Tach Board Installation Instructions:
https://premiumdashdecals.com/wp-content/uploads/2016/06/instructions_exact_reproduction_TB-OEM.pdf