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If I look at the records the PO gave me it looks like the speedo has had
problems in the past and the two documented "fixes" were both "tightened
connection of cable to sending unit". It doesn't appear that the sheath
is too long for the cable, has anyone had that problem? I guess that
would keep the cable from going all the way in but my futzing with it
seems to indicate that it does stick in far enough.
I suspect your problem may be that the squared end of the drive cable is
slipping in its receipticle. I've solved that problem by either bending
the end of the cable's squared portion so that the fit is tighter in the
receipticle, or butting a dab of JB Weld epoxy rin the squared cable end
before inserting in the receipticle. This condition can occur at either
end of the speedo cable.