Hi,

What's your problem now?

The speedo isn't working at all...

....or the speedo is just reading wrong?

In the first case make sure that the speedo drive in the box is turning, if
yes then make sure that the speedo cable is turning. If all those is true
and the speedo is not working, then it's defective. You can dismantle and
try to repair it.

In the second case, you need to make sure that the speedo drive ratio
matches your tyres, diff ratio and speedo.

It's not only changing the "output" gear, the "input" gear is also avaible
in - AFAIR - 3 different types (5,6 and 7 teeth??)

First you need to known how many turns your speedo will get per mile. On the
centre speedo, there's a number written below the odometer. On side mounted
speedos, this is somewhere at the back of the speedo, AFAIK.

Then calculate how many turns the gearbox will make when your wheel doesn
enough turns for one mile. The difference between those numbers is the ratio
for the speedo drive.

Sounds complicated, but there's a little program avaible on the internet,
which calculates that for you. You can find it in the download section of
www.minidevils.de Search for "Gearboxmanager"


Basically you can't make any changes in the speedo itself for adjustment.
Usually this is done via speedo drive ratio or some gears within the speedo
cable.

BUT - if you change the distance between the magnetic rotor and the needle
in the speedo, it'll read different. I guess, there's only one chance to
find that out: compare the odometer to the speedo needle. If they show
different readings, i.e. after driving 10min with 80mph or so than it
*might* be possible that your speedo is wrong. But this would be the last
possibility that I would think of.

....oh yes, another point: It *might* also be that the needle is misaligned
on it's axis. Usually there's a mark somewhere on the speedo where the
needle should rest at "idle"




HTH
Michael

Michael Heinzelmann wrote:
To give you an idea of value of the number you're looking for, one
common speedo in Australia has a calibration of 1425 turns per mile. A
metric speedo for the same car would obviously require a calibration of
about 890 turns per kilometer. (1425/890 = 1.6km/1km).

Obviously if you find a number of say 3000, that's too big to be a
speedo calibration, likewise anything less than about 500 would have to
be too small.

In fact adjusting the speed reading of the speedometer is relatively
straightforward (and cheap) for an instrument specialist, but the
odometer is geared and cannot be changed without putting different gears
in it.

I think they also increase or decrease the magnetisation to alter the
speedo response.

This provides a check that the speedo agrees with it's own odometer. If
it doesn't then you will never be able to get that speedo AND odometer
both to read correctly. Basically the idea is that if it takes 1425
turns to register a mile, then if you spin the cable at 1425 turns per
minute the speedo must read a mile a minute, or 60mph. If the speedo
reads 30MPH then any change you make (other than adjusting the speedo
mechanism as described above) which makes the speedo read 60mph will
also make the odometer read 2 miles for every true mile-on-the-ground.