Re: Speedometer error

[PGAHOWELLS <PGAHOWELLS@domain.elided>]

Hi
I wonder if your overdrive ia an "A" type. If so according to the catalogue,
there was a 18 and a 15 tooth drive gear. (I cannot for the life of me see
why. There seems only to have been one speedo head part number)
One takes 15 shaft turns to rotate the cable once, the other 18.
Admittedly the difference is 16.6% and not the 10% you allude to.
Try testing the mileage difference to the tenth of a mile with another car
with assumed correct speedo.
If the difference is 16.6% thats it. You have an "A" type with a 15 tooth
drive pinion instead  an 18.
Well that is one theory anyway.
If you have a "J" type this argument does not hold water. 
Peter Howells