1959 Cadillac - Fuel Gauge Not Reading Full?

[Dan Eckstein]

Hello friends,

I am reassembling a 59 Cadillac, and noticed an issue during testing the fuel sending unit that my fuel gauge does not read full.  I moved the fuel sending unit arm all the way up and it still only reads 3/4 tank full.  I even bent the metal stop tab out of the way on the fuel sending unit, but still the fuel gauge only reads 3/4 tank full.  The fuel sending unit is new.  Is that normal? 

Also does the fuel gauge system require a voltage regular?  Any help is appreciated.

[Dave Shepherd]

Dan, by design you bend the arm down some so the float goes higher, then it may read full, you could measure the depth of the tank, approximate the height of a full tank, use that measurement to see if the float arm moves thru that measured arc, if so the resistance may not match the dash gage.

[Matt Innocenzi]

Dan, take the lead wire for the fuel gage and connect it to ground.  When it is shorted to ground, it should read full and open circuit should read empty.  This will tell you if you are getting some resistance in your wires between the sending unit and the dash.

There is no voltage regulator - I believe there are some windings in the fuel gage to act as ballast and keep the needle from bouncing every time the fuel sloshes.

Matt

[Dan Eckstein]

Matt,

To clarify, which wire are you considering the lead wire?  Are you talking about the wire from the fuel gauge, going to the sending unit?


Thanks.

[Matt Innocenzi]

Dan,

Yes, I believe it is a brown wire.  It is the one that attaches to the stem of the sending unit.

Matt

[Dan Eckstein]

At the back of the car, I connected wire from the fuel gauge (which goes to the sending unit) and connected it to ground.  When I do this the fuel gauge reads empty.  When disconnect, the fuel gauge goes full.  So that works.

Solution:
The issue was that tube at the bottom of the sending unit was bent horizontal.   When it needed to be down at an angle to give the float arm more travel.  So I bent it down and now I can get more travel and the gauge read full.  

Oh happy days!!   THANKS EVERYONE!!!!