Hi Jim,
Old mechanical speedos like on our Healeys use spinning magnets driven
by the cable to "torque" a metallic disc to which the indicator needle
is attached. Resistance is provided by a spiral spring (think old watch
movements), which gets progressively wound up as the speed increases
(so, if anything, you'd think the speedo would indicate low instead of
high at higher speeds, but that doesn't seem to be the case usually).
As far as I can tell--I've had my speedo apart several times in the last
couple months--there is no adjustment to damp or assist the spring. You
can "calibrate" the speedo in a fashion by repositioning the indicator
on the dial, but you'll change the indication across-the-board (i.e. you
might read correct at 65 but read low at 45mph).
I suspect the characteristics of the movement spring change with age.
If anybody knows of an adjustment to damp or undamp the driven disk I'd
appreciate hearing about it.
bs
James Shope wrote:
> i regularly check my speedo with one of those "slow down" signs that register
> your speed. the max it will register is 45 and my speedo is normally right on
> or close at 45 but at 65 on the autobahn it is registering about 75 or so.
> is this common to healeys or am i looking at the second rebuild.
> healeymanjim
> _______________________________________________
>
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Bob Spidell San Jose, CA bspidell@comcast.net
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