[Healeys] Speedometer gearing

[Bob Spidell]

I've been able to dial mine in by moving the needle, even going from a 3.91 to a 3.54 rearend (since the change was a 
constant 11% or so over the entire range of the speedo).    If you look closely, there is a little white dot below the 
needle peg (where you would register -5mph if you could).  This is where the needle should be set for a std--in this 
case 3.9--rearend.  I just moved the needle up a tad and calibrated against a GPS and a gear/speed plotter I found on 
the 'net.

My understanding is that the drive magnet can be 'recharged' if necessary, but it's news to me that you can de/gauss 
aluminum.  Come to think of it, I don't believe Al is magnetic so I'm not sure the drag cup is made of Al.  Again, not 
sure about this--anyone know?

Bob


On 5/15/2011 5:05 PM, WILLIAM B LAWRENCE wrote:
> Actually calibration is accomplished by a special device that uses
> electromagnetism to gauss or degaussing the aluminum disc in the speedometer
> head to provide more or less magnetic flux acting against iron rotor. I
> learned this when I went in to bug Margaret Lucas about why she had my speedo
> so long. For that reason they can calibrate any speedo to run with about any
> gear ratio/tire diameter combination.
>
> I doubt very much if the drive gears on the transmission output shaft are
> different, although I think Triumph was into such foolishness. I think you
> could determine the truth by comparing the part numbers between the various
> models.
>
> Actually Per, the 3.545 gears are not as rare as they used to be. Contact Mike
> Lempert as he is producing runs of these batches of these gears. I have a set
> in my BN1 and it's like a magic carpet...
>
>
> Bill Lawrence
> BN1 #554
>
>


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Bob Spidell           San Jose, CA            bspidell at comcast.net

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