My '71 factory tach reads high (I have 4.56 gears using the gearing calculators!). I've read here there is an adjusting screw on the back of the tach. Can I adjust this with the car running and comparing it to a Fluke meter readout or is it for a 'bench' calibration only? TIA.

 

Mike, Before I sent my tic-toc-tach to John at Redline Gauge and Clock Repair for a tachometer calibration and clock repair, he made me peal back the foil sticker on the backside of the tach housing and calibrate it to my tach / dwell meter while it was hooked-up in the car.

So....the short answer is yes, you can calibrate your tach in the car.

 

Thanks Lance, I'll try that!

 

Well, today I pulled the tach and compared to a digital induction meter and sure enough it was off by about 800 rpms above 2000 rpms. I peeled the foil back and adjusted the phillips screw with it running (BOY is it sensitive!) and it worked perfectly. Thanks for the help again Lance!

 

John at Redline Gauge and Clock Repair stated that the deteration of the yellow paint on the needle hand (pointer) will cause the tachometer to loose its calibration. So...the adjustment and the needle are both VERY sensitive.

 

So just the loss of paint mass from the needle will affect it!? Wow that IS sensitive!

 

Yes, John stated that the needle (hand) is very long and "Z" shaped, therefore and loss of weight at the tip will greatly affect its calibration.