My '84 breadvan has a working speedo, but it is way too positive. I don't know whether these cars had a standard deviation like modern cars, but at 100 kp/h (GPS) the speedo is reading 115 kp/h. What could be the cause? just a worn cable?

The accuracy of the speedo has to be within 10% at 30mph (48kph) for UK rules and I would imagine it's quite a universal requirement so I would say yours is well within tollerance, I'm assuming you are running with the oem sized tyres ? as that will affect the accuracy 

most old cars are like this , new ones slightly more accurate but will never over read 

8 hours ago, nige8021 said:

The accuracy of the speedo has to be within 10% at 30mph (48kph) for UK rules and I would imagine it's quite a universal requirement so I would say yours is well within tollerance, I'm assuming you are running with the oem sized tyres ? as that will affect the accuracy 

Aha, I'll do that test. Tyres are from a '93 mk2f. 13 inch 165/65, don't know what the original for my car was but it can't be far off.