Speedometer - Over-reading error

[John Larkin]

The speedometer on my 1974 P6B (E suffix) UK-market automatic is over-reading by 17.5%. The differential ratio is correct (3.08:1), the speedo drive was new about two years ago, the gearbox is the original unit as far as I know, the tyres are 185/80 14", and the speedo itself is original. Has anybody got any idea what the problem might be? I'm baffled.

 

[Veetee]

I can't help, but have also suffered strange speedo problems. My P6B speedo was accurate until it recently failed, it was replaced by another with the same calibration which is running slow (like by 5mph at 30 and reading 60 when I must be doing 80). If I do not pay attention I will lose my licence-all those digital cameras in Nottingham! Got a replacement today to try from the ever helpful Ian Wilson of Bawtry.

Van

 

[Pete The Editor]

Has the speedo ALWAYS read wrong since you got it or is it a new thing?

I only ask as I believe the speedo heads for the S and the auto in Series two have different gearing. I will see if I can find out.

Try to find someone with the same car and check all the little numbers / letters on the speedo to see if they are the same on both cars.