[Supras] Non-linear speedometer

[berniek at technicaldevelop.com]

The indicating needle is balanced, usually with a very small counterweigh
that is micro-spot welded or glued on.  Fundamentally, the speedometer is
comprised of a magnet rotating within a "drag cup", an aluminum cup which
tends to rotate with the magnet due to eddy current induction.  However it
is restrained by a hairspring, so the equilibrium position of the drag cup
and the small shaft which drives the needle are linear with respect to
speed.  So if the needle is out of balance, that may be the source of
error.  There are small pullers meant for removing pointers from pressure
gauges for recalibration, or you might be able to pull the needle off with
needle nose pliers on the shank, with a small piece of wood as a fulcrum
at one of the faceplate supports.  Either use the old needle, or rebalance
the new one by allowing it to seek its heavy spot by supporting it on thin
wire, and adding a few fibers of wood or things like #2 lockwashers on the
rear of the pointer.


If your odometer behaves the same way, the problem is elsewhere, perhaps
in sizing and skipping of the driven gear in the transmission.

Hope this helps.

BernieK