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'55 gas gauge/sending unit

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  • '55 gas gauge/sending unit

    New gas tank sending unit from SI installed. NOS gas gauge installed.
    Have had 5-10 gallons of gas in the tank the last year with no reading at all. Added 5 gallons today and the needle finally popped off the below E mark to just at E, maybe slightly above. Ran an external ground from the sending unit all the way to the battery terminal so ground not a problem. I get current at the sending unit connection at the tank. Can remove the sending unit from the tank and manually move the arm up and down and the gauge responds nominally. The sending unit float is indeed touching the gas. I'm thinking something must be wrong with the arm length when installed? Any ideas?

    '55 Commander
    '55 President
    \'55 Commander
    \'55 President

  • #2
    what happens if you (briefly) touch the red wire to ground?

    What happens if you ground (briefly) the red wire at the back of the gauge?

    Is your gauge panel well grounded?

    nate

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    55 Commander Starlight
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    • #3
      Red wire at the sending unit to ground does not peg to Full as expected, but the gauge just went to 1/2 setting.
      Grounding the same red wire at the back of the gauge oddly takes the needle over to 3/4 only, on two tests.
      I put an additional ground wire from the gauge cluster mounting bracket to a good ground during the second test.



      '55 Commander
      '55 President
      \'55 Commander
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      • #4
        Additional test:

        Red wire off sending unit to VOM and the black tester wire from the VOM to a chassis bolt reads 6.23-6.25 Volts.

        However, red wire off the sending unit with the black wire from the VOM routed to any of the 5 or 6 sending unit installation screws and all I get is 2.68-3.23 volts.

        This would seem to indicate poor ground, but the sending unit is installed in the standard manner of the screws through cork gasket into the tank. The threads were NOT painted but cleaned before installation of the sending unit. Painted tank should not have any effect here since I'm essentially making these connections on the sending unit itself by using the installtion screws.

        '55 Commander
        '55 President
        \'55 Commander
        \'55 President

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        • #5
          based on your second test, I would suspect a bad gauge, but your third post indicates that you also may need a better ground at the tank... lots of fun!

          I wish I had the specs on resistance to ground at various arm positions for a '55 sending unit, but I don't. I didn't have to do a thing to the one in my car, so I'll be little help.

          nate

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          • #6
            Tank itself may not be grounded. I ran a ground from the sender on mine. You could run a hot and ground to gauge from battery(make sure connections are tight) and ground sender wire at gauge and check for movement. If not full would suspect gauge. If functions properly
            you could have a voltage drop into the gauge. You could check voltage on switch side of gauge and check again with sender wire grounded.

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            • #7
              I think I have another gauge of uncertain reliability, but I will try to find it and run a test with that gauge off the car.

              '55 Commander
              '55 President
              \'55 Commander
              \'55 President

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              • #8
                Well, I went back into my notes over the last 18 months or so and had written down that two other fuel gauges I had both reacted very slowly and both would stick on Full and not return. I then installed a NOS gauge but could not get an output reading on it, so it was returned and another one installed and confirmed 6V at the red wire terminal of the gauge. My notes indicated the temp. gauge was also not reading and I installed a NOS one of those as well. Longest drive so far in the car was this past Monday about 5 miles and I noted the temperature gauge barely came off the lowest mark and the gas gauge did nothing. It is very odd that I cannot get a test light to illuminate but the VOM shows 6 volts both at the gauge terminal and at the sending unit. But no gauge readings. Since I previously had the problems with other gauges and now two NOS will not read, there has to be something happening I just cannot find. When I installed the NOS gauges, I substituted thick cork for where the back of the gauge cluster had the thin cardboard isolators as the carboard was just in too bad shape. Ammeter works fine and of course the oil gauge is mechanical.

                '55 Commander
                '55 President
                \'55 Commander
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                • #9
                  I am not sure if I understand your situation correctly, or even how these things work, but I was under the impression that the dash unit is isolated NOT grounded (hence the isolators), the sender is sending varying ohms of resistance (GROUND) to the gauge depending on float position to move the dash gauge needle.

                  Therefore, you should have 0 Volts at the sender end of the wire! And various OHM readings at the gauge end of the tank wire depending on where you move the float to.

                  When you revert to harness and frame power rather than jumpered power, you will want to be sure you have the correct large gauge braided Positive ground cable from the Batt. to the water manifold and engine to frame, also a very heavy gauge (6V) Negative cable to the solenoid.

                  StudeRich
                  Studebakers Northwest
                  Ferndale, WA
                  StudeRich
                  Second Generation Stude Driver,
                  Proud '54 Starliner Owner

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                  • #10
                    If I remember correctly there are two basic types of fuel gauges generally used. One uses a bimetal strip & the other uses coils.(I think, AC and S-W respectively are examples). They both work by varying the current through them with the float resistance unit. If you read the resistance on a SW sender(for SW GAUGE) should read near 0 Ohms when arm is down, around 240 when up. AC will read lowest with arm up(0 ohms?) and largest with arm down(90 ohms?) I believe the bi-metal type will work without a ground, but the coil type need the gauge grounded to function. To simplify one coil pulls to E (grounded in gauge) the other to F (grounded in sender). You should have voltage in and out of both gauges but the voltage(especially out) would vary by float position with lowest at lowest float resistance.(sender disconnected should have full voltage in and out) Always ground a gauge as most people don't know what type they have and it's needed for the light. I think Stude gauges are coil type(SW)

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                    • #11
                      Not to mislead anyone SW float is 240-33 ohms for to 12 volts. 6 volt gauge may or may not be the same. I may also have reversed position of low and high readings. AC also seems to have made both types. There are several variations of both types by different manufactures.

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                      • #12
                        I installed an NOS gauge unit in my 52, nothing worked, sent both gauge and sending unit to John Wolfe & Co. in Ohio. They repaired both units, gauge works great. They told me there was a broken wire on the gauge even though it was an NOS unit. (but 50 years old)

                        Jim
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                        • #13
                          OK, we got back on the gas gauge problem today and determined that the new unit is faulty. I still had the old unit off the car, checked the float and it floated so I installed it (with external ground) and the gas gauge works perfectly. By external ground I just mean I ran a ground wire from one of 5 the installation screws to a known ground ground. What is wrong with the new unit I don't know. It works off the car via a manual raising and lowering of the arm, but did only go to about 7/8 instead of a full reading. Back on the car it does nothing. Float does reach the gas since tank 3/4 full. Arm, while different from the original unit on the car, seems to track the same path. We thought it might just not be raising up, but we checked the float off the car and it floats. Just cannot determine what the problem with it is, but with all things being equal the old unit works and the new doesn't. Since I've had the unit for a year or so I doubt the vendor will take it back even though the car only took it's first trek last Monday in several decades.

                          '55 Commander
                          '55 President
                          \'55 Commander
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