Anyone know how these old singer foot pedals work? There's not much
to this thing, but I can't for the life of me figure out how it's
supposed to work!

The one I have contains a long ceramic tube filled with a stack or
maybe 100 graphite disks. One end connects to the sewing machine
motor (I assume), and at the other end there's a contact that's
brought closer to and eventually touching the contact on the end of
the tube as the foot pedal is depressed.

The foot pedal was dropped and I'm trying to repair it, but so far I
can't get any variable speed out of it - I get either off (when the
contact isn't touching the end of the graphite-disc-tube) or ON-HIGH
when the contact touches the end of the graphite-disc-tube.

Sorry for the miserable description - it's been about a month since I
had the thing apart - just figured I'd post here to see if anyone had
any suggestions.

thanks!

-Pete