When I pulled the sender out of the tank, it looked terrible: so full of
crud and corrosion and rust that it was stuck solid at the half way point.
It looked like it was dead, but with a lot of penetrating oil, careful
scraping and wire brushing, it actually moved again! The cork float is
attached to an arm which is hinged from a support extending down from the
sending unit. As the float moves up and down, it rotates a small gear which
is meshed with a second small gear which in turn rotates a rod which goes
straight up into the sending unit. This rotating rod changes the resistance
in the sending unit, which controls the movement of the needle on the gauge
face.
Anyway, now I had a moving sending unit. I hooked it up to the gauge and
connected 12 volts to the system. When the float was at the bottom, the
gauge read 1/4 full, and when the float got near the top, the needle pegged
past the point of being full. No problem I thought, that's what I get for
running a 6 volt gauge system on 12 volts. I rigged up a 6 volt source, but
got the same basic dial movement on the gauge. Rats, no good at all. As I
contemplated bending the float arm or buying all new stuff, my eyes fell on
those little gears again. As I watched them turning while I moved the float
up and down, I suddenly realized I could use them to calibrate the gauge.
Still using 6 volts, I let the float all the way down and the gauge showed
1/4 full again. I carefully spread the little gear teeth and moved the gear
attached to the rotating rod back one tooth. The gauge now read 1/8 full.
I did it again and the gauge read empty. I then moved the float all the way
up and the gauge read full. Perfect! I don't know if this will work in all
cases, but it may be worth a try.
Mike Bennett 1944 DUKW
Fresno, California
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