RE: [Chrysler300] fuel tank sending unit

["Rich Barber" <c300@xxxxxxx>]

I've spent some time on the fuel gauge system in my 1955 and learned a few
things, not necessarily in order of importance:
I made a variable resistor set from Radio Shack components and determined
the following resistances at the connecting wire in the trunk were required
to drive the gage as indicated:  Empty-75 Ohms, 1/2-35 Ohms, Full-10 Ohms.
I use these values to calibrate and adjust the wire on the float.  I also
connect my Ohm meter to the output connection of the sender and its frame
while manually operating the float.  This enables me to evaluate the
continuity of the float's variable resistor system.
The wire from the sending unit is routed under metal tabs in the floor of
the trunk.  I wrapped that old wire with black tape to make sure it was
insulated from the ground.
I sent my sending unit to a guy for rebuilding.  The variable resistor and
contact wiper were different from the original and only sorta work, with a
lot of spastic motion of the needle and uncertain full and empty points.
I did add a ground connection from the top of the sending unit to a good
ground in the trunk and that helped.
Always empty indicates an open circuit, or the float has sunk.  Possibly a
leaky brass float or a saturated cork? 
The fuel gauge has one connection to the switched side of the ignition, so
the gauge will not work unless the ignition is switched on.
(Non-electrical) Sealing the sending unit to the tank is a challenge--I'll
try the motorcycle oil filter seal recommended by a member.
No matter what I do, the fuel drops like a rock in a well when I open up all
eight barrels! But, it's worth it.

Let us know what you find and the year of your Brute.

C-300'ly,
Rich Barber
Brentwood, CA
1955 Chrysler C-300



-----Original Message-----
From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx] On
Behalf Of David Zakarian
Sent: Friday, June 29, 2007 1:49 PM
To: chrysler club
Subject: [Chrysler300] fuel tank sending unit

I know I'm doing something stupid, I just don't seem to figure out what, so
I'll ask and give y'all a good laugh to start the week-end.

The problem is the send unit will not send the message to the gas gauge on
the instrument panel that the tank is full.  It reads empty regardless of
the amount of gas in the tank.

This is what I know:

The tank sending unit works.  I've run a jumper from the line to the tank to
the sending unit and as I manually move the float up and down(while
grounded) the gas gauge goes up and down.  This also tells me that the gas
gauge works.

With the tank unit installed in the tank I have run jumpers from the tank to
the frame and from the flange that holds the unit in the tank to the frame.
So I think I've grounded everything.  the tank unit still reads empty on the
gas gauge.  Works the same with or without the jumpers on the tank and the
keeper flange or the sending unit.

What am I missing, that is besides my sanity?  Yes there is gas in the tank.

Thanks for your help and your welcome for the laugh

Zak

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