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Re: [T3] My Notch's Tranny


On 6 Nov 2002, at 19:08, Keith Park wrote:

> Interesting... but wouldnt the magnet lose strength with age and cause the
> needle to not raise far enough giving too low a reading??

No, magnets don't lose strength with age. While there ARE things that can 
demagnetize them, age is not one of them.

> I dont expect it to be perfect but wouldnt my raising the spring pressure
> bring it back closer?  my error isnt linear... its about 5 or 6MPH at 55..
> the gets  to near 10 by 80. 

The little spiral spring is made long so that it can be fairly linear. I don't know 
whether the eddy current drag that pulls the needle around produces a linear 
drag, but I've always assumed that it probably was, or that the non-linearity 
was compensated for by the way VDO painted on the scale.  

Of course it is always possible that your needle has gotten moved on the 
shaft, and that you need to put it back. Then you have to guess where it 
should go. I think that on Beetle speedos there is a tiny paint mark where 
the needle should rest if you lift it past the stop, but, unfortunately, ours do 
not have that feature.  

> I also notice that this speedo suddeny jumps off the pin as the car gets
> over 10MPH or so.... Crappy Speedo! 

I've seen some speedos where lube from the pivot got down to the needle 
rest and made it sticky. These will build up force and then jump off the rest. 
It is also possible that the pivot is dirty and needs a cleaning and some 
careful lubrication.  

Some of mine have let me get above 40 mph before they will pop loose on 
their own. Sometimes I have to tap the face to fix them.   

The fact that VW used them indicates that the VDO gear was fairly cheap, 
but the VDO stuff in Mercedes and BMW are the same, so I think the quality 
is generally pretty good.

-
*******************************
Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
*******************************

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