I have looked at a bunch of websites with no luck. But someone here is sure to know. All the mechanical tachs I am familiar with work the same, with an eddy current disc and a spinning magnet. I figured this out when I fixed a speedometer in a VW Bug way back in 1980. But I have seen several antique race cars with tachs that don't seem to work this way because the needle moves in a jerky fashion. It will swing fast to a position and then stop. The rpm will then audibly change and there will be a time lag before the needle quickly swings to another position and stops dead. It's as if the needle can only move in discrete steps. I can't figure out why this is, if it's done on purpose, or if it's desirable. I have seen this type of action on several different makes of race cars. So, who here knows about this? If you want to see this in action search Youtube for the TV show "Victory By Design". If you like cars at all, and race cars in particular, and have never seen any of these shows then by all means look it up. A retired race car driver, Alain de Cadenet, does a wonderful job driving and showing off the cars. His obvious joy driving the cars and his obvious skill driving the cars makes for a really enternaining show. He talks about brakes, engines, suspensions, frames, superchargers, carbs, etc. But he never says anything about the tachs. Eric
- posted
7 years ago