Mechanical VDO Speedo reading low

[Grin-a-lot]

As above, my VDO mechanical speedo reads low by 10 mph consistently.  When stationary it does read zero though.

Any ideas on where would you start with fault finding?  My gut feeling is that a broken cable would give a sporadic reading so perhaps it's one of the ends of the cable.

Since the speedo reads zero when static I assume the dial is mounted on its shaft correctly and hasn't slipped so the speedo is ok.

The error is consistent and not proportional to speed so I think that rules out a calibration issue.

I've got a spare electronic speedo but no sender.  Is it worth just replacing with the elec speedo and buying a sender rather than attempting to diagnose the current one?

Any advice on wiring in an electronic speedo gauge?

[David H]

Might be that the needle has shifted by 10mph which is why it is constant. Calibration would be out by a ratio rather than a constant...?

[Daley Down Under]

Reading 10mph low consistently does sound like needle shift.  At rest, needle will be against the stop (it cant read -10)

[Grin-a-lot]

It does sit on the stops at rest so I'll have a stab at needle shift first off.  Hopefully google will be my friend!

[Hairy Santa]

Does it read anything up to 10MPH, or start to read from there

[Grin-a-lot]

Come to think of it I don't know.  I'll have a look when I get home at the weekend.  I guess if it only starts to climb from 10mph then needle shift is looking more and more likely.

I found a guide on Internet that suggests it's held in place by friction so some gentle clockwise turning might do the trick.

[YellaBelly]

I am watching this with intrest as my speedo is a mechanical VDO and I've no idea how it will match to my type 9 speedo drive ratio.....