Re: [AMC-List] 65 American speedo

[Tom Jennings <tomj@xxxxxxx>]

> On June 18, 2006 Gary L. Kirk wrote:
> 
> > Does anyone know anything much about the speedo on a 65 American
> convertible. It seems to be made by King Seeley. I can't figure out how 
> it is supposed to work and what causes it to work and or not work. Is
> it magnetic or?

They're wonderfully simple -- the cable from the trannie spins a bar
magnet inside an aluminum cup.

The speedo pointer is attached to the aluminum cup. There's a light
spring that returns the pointer to zero.

The spinning magnet induces electrical current in the aluminum cup;
since it's just a big short the current turns immediately into a
magnetic field. The faster the cable/bar magnet spins, the larger the
current in the cup. This attracts to the bar magnet, pulling the
cup/pointer up the scale. One of those breathtakingly simple, reliable,
accurate things that went unchanged for 60 - 80 years.

Pretty much nothing ever goes wrong with them. The cable wears out
though, and gets kinked from being attached to an old car. About 99.9%
of speedo problems are in the cable.

The speedo in my 70 Hornet has a little problem; the bar magnet is
scuffing ever so faintly inside; you can hear it in the dash cluster (a
faint ching ching ching...) at 20 - 40 mph. Probably I did this, when I
had the dash cluster apart on my bench for a few months while restyling
it.

You should never lube the dash unit. The pointer/cup pivot has no force
on it and barely moves, there's no need to touch it.

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