The speedo is driven electronically with a square wave signal generated
from the gearbox. The converter chip reduces the frequency by the ratio
of Kilometers to miles. There are dozens of these converters (Chips) on
the market and most are unreliable and will break down eventually due
to inadequate spike protection. There are some good ones available but
you need to know the difference. Be aware that a failing converter can
cause other error signal problems which may not be immediately apparent.
Fitting the converter is a simple matter of cutting the 2 signal wires and
routing these through the converter and then adding a power supply to
drive the electronics. The power supply is best obtained from the radio
supply which becomes live with the ignition on. You also need to paint
out the speedo face "K" ie: Km/h = m/h.
Other than reliability, the only problem is you have a speedo which reads
0 - 180 Mph which is more difficult to read at exactly 30 Mph and many
owners are more comfortable with a speedo which reads 0 - 120 Mph and
is certainly more realistic.
Fitting a new faceplate involves removing the speedo needle, replacing
the faceplate and then refitting the needle. The problem is finding the
exact position when replacing the needle. If you replace the needle with
it resting against the stop it will be reading approximately 5 Mph too
fast because there is a small amount of tension when the needle is against
the stop. To calibrate it accurately requires some patience.
If you have, or can borrow a portable sat-nav then you can calibrate the
speedo to an accuracy of 0.1 Mph, or more realistically 1.0 Mph, at a
constant road speed of say 50 Mph.
Fitting a new faceplate will not change the odometer and they will both still
read in kilometers, however, most owners do not find this a problem and
even an advantage if you often drive in metric countries.
Personally, I much prefer a new MPH dial and would not fit a converter
"Chip" and I never venture "Abroad", however, the choice is yours.
