SPEEDO ISSUE

[AshleyO]

OK
Smiths speedo
reading from a strobe on the propshaft
IVA man said it was the most accurate he'd ever seen. Feather in cap
BUT
Now it's fine, but if I go over around 60mph, then even when I slow down, it is over-reading, and won't re-set until I turn off the ignition and on again
Have tried Caerbont but no answers forthcoming
Anyone had such an experience or any ideas where to start??
I am stumped
Thanks

[greenwoo]

no idea.....
but is there a different set up option related to the positioning of the sensor...ie/ if its on the prop then it'll be spinning far more quickly than if its attached to something at the wheel end.
out of interest does it behave the same in all gears - ie/ does it invariably go wrong at 60 in 3rd/4th/5th? if so my logic isn't likely to be right....

[Fury1630]

Is it live axle?
If so the prop will move about in relation to the pick-up when the axle moves, is it moving out of range on the overrun & confusing the speedo?
Still sticking with the assumption it's live axle, is the pick-up at the front of the prop where it won't move so much?

How many magnets have you got, could it be that over 60 one magnet is "coming into view" before the last magnet has left? One less magnet & recalibrate?

On mine I got fed up with all the magnet business & fitted a Fiesta Mk IV (from memory) speedo sender to the type 9 & calibrated to that - no problems since.