[Shotimes] Spedometer problems...

[George Fourchy]

On Mon, 22 Nov 2004 14:18:31 -0500, J.R. wrote:

> I noticed a
>high pitch noise coming from the instrument cluster area of the dash and
>took note that the speedometer was reading an insane speed well over what I
>thought it should, 

I can tell you what I think is happening, but I cannot tell you why (for sure).

Mechanical speedometers work by magnetic induction.  There is a U shaped magnetic
yoke that spins around a disc that the pointer is fastened to.  The cable is
attached to the base of the U shaped yoke, and it spins around the edge of the disc,
inducing it to move by magnetic force.  It moves more the faster the yoke moves.  I
suspect that for some reason, the yoke, or the base of it, one or the other or both,
is intermittently touching the disc.  When they touch, you hear the scraping, and
also the needle will bounce around, since it is being 'pushed' by the yoke or cable
end.  The odometer is not affected because it moves so slowly you can't tell; also,
it is directly geared to the cable below the yoke.

I don't know why this happens, but I suspect it can be remedied by stretching the
cable housing a bit, so that the top end of the cable does not push on the yoke
assembly when connected.  If one could hold both ends of the housing and pull just
slighly, the housing would be a tad bit longer, so that the cable itself would not
push out so far from each end.  I wouldn't pull it from the firewall side without
removing it from the speedo, due to not being able to tell how much tension you are
putting on it...you might break the back of the cluster (it is plastic, after all,
and these cars are WAY past their original lifespans).  On thinking further, one
might be able to just stretch it from where it goes into the firewall down to the
end.  I cannot tell you why the cable stretches.  It doesn't matter on the bottom,
where it connects to the short piece that goes to the SS, but it seems to on the top
end, where it pushes the part that it plugs into at the back of the speedo head. 
The black car that replaces the Lowrider had that problem after the new engine was
installed by Zach in my driveway (it didn't before, when it ran really loud with the
spun bearing).  When Mark Nunnally got it, he just swapped in a different gauge
cluster, and it quit.  It might have also quit with the original one, since the
cable was disturbed when he unplugged it.  I have to get the car back to explore
this more....I want the other speedo back in it, since its mileage is accurate.

More later......sometime....(when the black car is home)!!

George