Speedometer records speed but doesn’t drop back

[Tipidave]

All has been well with the herald save for a sudden onset change to the operation of the Speedo. It seems to rise correctly but then does not drop back unless tapped on the glass with some force. So in effect is is just recording maximum speed achieved. Now, being a 1200 speeding is never really going to be an issue… but I have no idea where to start… new cable about 18months ago. Not used much over winter but out and about for around 400miles so far this year. Sudden onset.  Any ideas???? 
 

[Colin Lindsay]

That's possibly the return spring on the needle sticking, so it needs the gentle tap to free it up. The cable will make the needle move up, but won't affect it not dropping back, so you can discount that. You'll need to dismantle the speedo, remove the glass by twisting to line up the small lugs on the rear, but then you'll also have to undo the screws on the rear to access the spring mechanism which is behind the dial. A gentle clean with something like Servisol should free things up, or you may be able to spot something stuck in the mechanism. Gentle is the word, the mechanism is quite small and very easily damaged.

[Pete Lewis]

yes remove the rim and glass 

undo the two screws holding the mechanism 

add a small dot of oil to the needle spindles 

do not remove the needle thta would cause complete decalibration 

do check the fine hair spring is intact thats the return method 

if its failed you cant do much DIY 

Pete

[PeteH]

Grease, or Oil has likely got into the "works"?, tends to make the more delicate instument parts Sticky with the result you describe.

Pete

[Tipidave]

Thanks for the prompt replies… one slightly alarming aspect to the drop back to zero is the ‘loose and floppy’ fall back. Did wonder if a return spring had failed. It will have to wait a week or two as I am away but I will then proceed with caution as advised 😀😀👍👍🧐