Speedos work by magnetic "drag" between a magnet spun by the cable and the
spring-loaded needle (what you see on the dial) via a metal plate. The faster
the magnet spins, the more force is exerted on the needle, the further the
spring is deflected and the more the needle rotates. Could be that a little bit
of crud or something blocked the needle's movement, and then worked itself loose
a few miles later.
Gary McCormick
San Jose, CA
SRL311-13291 whose speedometer functionality is a moot point at the present
time ;^)
"David R. Conrad" wrote:
> > List:
> >
> > This is *very* OT, and I apologize, but I'm puzzled, and perhaps
> > someone can answer this.
> >
> > My speedometer/odometer suddenly stopped working yesterday, and
> > just as suddenly, about 10 miles later started working normally
> > again.
> >
> > If it is, as I've always thought, a strictly mechanical matter, I
> > don't understand how that could happen.
> >
> > The speedometer has been noisy for the last two years or so. I
> > went so far as to buy some lubricant, but crawling under the
> > dash, couldn't figure out any way to get at the cable. Gave up
> > on that and just lived with the noise, figuring i'd take it to a
> > GM dealer for repair when it finally gave out.
> >
> > The car has "cruise control", and I thought that might use an
> > independent speed input than the speedometer. Apparently not,
> > because, during that period of outage, it wouldn't work either.
> > It now does, again
> >
> > The noise also seems to have gone away.
> >
> > Can anyone explain how this could happen. A broken cable
> > certainly can't repair itself.
> >
> > Dave
> > '68 1600
> > Kailua-Kona
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