[DeTomaso] Speed error and how the mechanical speedometer works

[michael@michaelshortt.com]

Thanks for the primer.

Michael




On Mon, Mar 9, 2009 at 3:55 PM, Dagny Kristine Bakken <dagny-kr at online.no>wrote:

> In a mechanical speedometer, a rotating cable is attached to a set of gears
> in the automobile's transmission or one wheel. This cable is directly
> attached to a permanent magnet in the speedometer assembly, which spins at
> a
> rate proportional to the speed of the vehicle. As the magnet rotates, it
> manipulates an aluminum ring, pulling it in the same direction as the
> revolving magnetic field; the ring's movement, however, is counteracted by
> a
> spiral spring. Attached to the aluminum ring is the pointer, which
> indicates
> the speed of the vehicle by marking the balance between these two forces.
> As
> the vehicle slows, the magnetic force on the aluminum ring lessens, and the
> spring pulls the speedometer's pointer back to zero.A correction can be
> done
> by repositioning the needle to the pin its often mounted to.A thing often
> performed by shops specialiced in instrument restoration/calibration.Hope
> this helps :)
>
> Øyvind Bakken
>
> -----Opprinnelig melding-----
> Fra: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com] På
> vegne av JDeRyke at aol.com
> Sendt: 9. mars 2009 06:47
> Til: michaelsavga at gmail.com; detomaso at realbig.com
> Emne: Re: [DeTomaso] Speed error
>
> The speedo head drives a separate geartrain inside the speedometer case to
> turn the odometer dials. Thus there's a chance one function will be
> accurate
> and
> the other off at some, or all, speeds.   In running T & D rallies years
> ago,
>
> I found the stock odometer, with 26-1/2" OD rear tires, to be very
> accurate-
> at least at the speeds rallies were run (always a legal speed). During this
> time the speedo was always optimistic. You're probably better off using a
> calibrate-able electronic unit, but even then, one function may be more
> accurate than the other- dunno how the mechanism inside works. Good luck- J
> Deryke
>
>
>
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-- 







Michael L. Shortt
Savannah, Georgia
www.michaelshortt.com
michael at michaelshortt.com
912-232-9390


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