Speedo Cal

[William2]

Having just checked my speedo for accuracy against a satnav it appears to over read by about 6/7mph. The car has a 3.77 diff and the correct green coloured speedo drive gear. It is an S4 but has the 1000tpk earlier type of speedo. I was wondering, is it possible to try and tweak the speedo yourself to improve the accuracy or is the only option to send it off to Speedy Cables or a similar company?

[ericbushby]

If it is a constant error throughout the range, it can be adjusted by moving the zero setting.
At rest the pointer should be at the tiny white dot below zero.
You have to gently work the pointer over the wire spring zero stop to check this.
The pointer can be pulled off and replaced a few MPH lower if you think it will help.
Small levers and dial protection are needed.
if the error is erratic, then I think it is a job for the specialist.
Hope this helps
Eric in Burnley
1967 S3SE ( will be at Tatton Park on Saturday if fine )

[john.p.clegg]

Tyre pressure,Tyre sizes?

John in Manchester
1969 Plus2 ( will be at Tatton Park on Sunday no matter what the weather is like)

[elansprint]

When comparing with a sat nav this has to be on a perfectly level road as any form of gradient you will have travelled further than the sat nav thinks. Personally I would leave it alone at that
Ian

[AHM]

satnav works in 3 dimensions so speed should be reasonably accurate as should height above mean sea level.

Speedos, depending on the type are calibrated by adjusting the proximity of the magnetic plates. The zero setting should be unchanged if it is correct.

It is possible to do it yourself but you have to take it apart to make the adjustment. And you will need to know the inaccuracy at the indicated speed of your electric drill.