Speedo Calibration - fixed (nearly)

[rdl001]

The speedo of my 1996 Chim has always read over 20% too fast through the whole speed range. After reading many threads around speedo calibration it seems that about 10% is acceptable to most people.

This is what I found,
When measuring the gap between the sensor read head and the 'teeth' of the diff I had variation in the gaps between 0.2mm to 1.4mm. I found that one of the 'teeth' was bent up and three of the 'teeth' were bent down which gave the variation. The sensor is an inductive proximity switch which picks up the leading edge of each 'tooth' for an 'on' pulse and the lagging edge of each 'tooth' for an 'off' pulse producing a square wave. Most inductive proximity's have a slight hysteresis between the 'on' and the 'off' trigger distance so the consistency of height and width of very 'tooth' is very important.
I spent many hours bending a filing my 'teeth' until the gap with a feeler gauge was exactly the same on EVERY 'tooth'.

The accuracy of my speedo instantly improved to 8% through the whole range. Also, I increased my sensor gap from 0.3mm to 1mm and still get 8%.
Now I am happy, this may help other with a similar problem.

Regards,

[rdl001]

Unfortunately my speedo does not have any trim adjustment on the back

[rdl001]

Tried it, this item does not work well with a 2 wire proximity device