Tachometer calibration

[chewychevy67]

This is why I got a 4k diesel mechanical tach and had member tbone1964 recalibrate it to 5k and he also rescreened the face to a 5k as well. He did a great job. Also had to get a distributor with the tach drive as well. I have not used this yet as my truck isn't complete but I'm hoping it will be more accurate than the electronic tach.

[custom10nut]

To hear the frustration some go through with the factory tachs.
I’ve not had any issues with either one of mine.
For many years I had a used one from a 72 Blazer, and never had an issue with it, even when I put a Mallory Electronic Conversion kit in the Distributor, to replace the points, until one day the Diode in it “Gave up the Ghost”.
I replaced it with a new factory model, and it works great.
Gauging it against my Digital Multi-Meter Tach it’s within 20 RPM, so I’m not messing with something that works.
I must be fortunate, because I don’t have any of the mentioned isssue.
Good luck on figuring out the problem.
And about your adjust me t question.
Yes the screw on the back IS the adjustment screw for “Fine Tuning” the Tach.
It helps to have someone helping you, because you have to be laying on your floorboard while you adjust the screw. Good Luck

[425HP409]

I found a previous thread that addresses calibrating it with an adjusting screw that is at the top rear of the tach that is covered by tape.

[leftybass209]

I can add that, I have a tach that was reading low, also HEI. I assumed the board was bad and replaced it, using a new board from Cajun Tach shop. It still reads exactly the same, and has a hangup where it will freeze.

I assume the issue is with the physical mechanism needing recalibration, not the electronics.

[425HP409]

I hooked up 3 tachs to a car with a digital timing light for a reference tach and 2 calibrated perfectly throughout the rpm range with the screw in the back. The 3rd would calibrate at idle, but read 2000 when it should have been 2500. I have 2 more to check tomorrow. ps: The test car had HEI and one of the tachs had previously been in my truck with point ignition. It read the same before calibration with both ignition sources. The tack reads ignition pulses, and doesn't care if it is HEI or Points.

[Already Gone]

Originally Posted by leftybass209

I can add that, I have a tach that was reading low, also HEI. I assumed the board was bad and replaced it, using a new board from Cajun Tach shop. It still reads exactly the same, and has a hangup where it will freeze.

I assume the issue is with the physical mechanism needing recalibration, not the electronics.

Oh goody. I have one of Cajun Tach Shops new Circuit Boards for my tach and was hoing was going to sure my not reading accuaratly problem . I am using a Petronix stock look distributor.