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I thought it would be a straight forward swap kph speedometer to mph. Oh no, as I
drove the Spider up the road I'm thinking, seems a bit fast for 40 mph! It was, actually it was 57 mph
which I found out by downloading a speed app onto my smart phone and then retry to proved
it.
I racked my brain thinking, if a full sweep of the clock is 320 kph and 200 mph and halfway (top of the gauge)
is 160 kph and is 100 mph, then why is it under reading by so much?
No one I asked could tell me what was going on. I knew it wasn't a faulty speedo because it was
the second speedo I'd had. The first one was under reading, as was the second speedo. But
the first had a short pointer - stop or pin and the pointer went below the pin and didn't
register any speed at all. I did flick it over the stop which made it work, but it would revert back to
below the stop.
There is only one sender so it can't be that. My car was originally a Swiss car and it turns out they
have slightly different gearing to "Rest of the World" which led me to think the difference had to
be in the speedometer heads. Eventually I realised the number of impulses per equivalent mile / kilometer
was different and if I change the KPH motor onto the MPH speedo it should work.
While taking them apart I realised I would need to change the odometer drive if that was to work
accurately.
As I drove up the road checking the speed with my phone GPS speedo, my smile went from ear to ear, it was
spot on as was the odometer. I'm keeping the KPH speedo so it can stay with the car. After nearly a
year another job finally well done!
