View Full Version : TR2/3/3A TR-3A Testing Tach and Speedometers

09-09-2006, 03:20 PM
Dragged out my guages this afternoon and wondering how to test them and see if they still work. How would I do that? By the way the original speedometer has 95,000+ miles on it!

Anyhow, Thanks for any thoughts

Geo Hahn
09-09-2006, 03:55 PM
You can rig up your electric drill to drive the heads on these. Best thing is a bit of old speedo cable as it has the correct end on it though I have also used a finishing nail with the pointy end filed/grindered to a square and the head smoothed away.

Look at the max RPMs on the drill to get an idea of what full on will produce. Tachs usually stay fairly accurate over time (in my experience) but speedos lead a harder life.

Roughly, the speedo indicates mph as RPM/50... e.g. 3000 RPMs will make it read about 60 mph.

Lots of good speedo/tach info here: