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Thread: Sending unit troubleshoot

  1. #1

    Sending unit troubleshoot

    1949 Willys Jeepster

    Hi All,
    Added to the list of small things make for interesting problems. Ever since I got this beauty the gas guage has always been pinned at E. I've read all the links from previous posts, have a mild understanding of variable resistors, etc.
    I took the gauge out, checked it over, found 1 of the tiny hair like wires was broken off the post. Soldered back. Applied current to it and it moved the needle on the bench test. Put it all back together, added 10 gallons of fuel and turned on the power. Nothing.
    Checked the continuity of the wire from sending unit stud to gauge. Worked. Needle moved. Checked ground on tank. Jumped the circuit and it moved the needle.
    I concluded an issue with the sending unit. Ran the gas down road testing, more fun than siphoning. Dropped the tank and tested the continuity again just to be sure wiring and gauge work. Bench tested the sending unit and sure enough no change in resistance.
    Knowing I can buy a new sending unit for $40 I got brave and drilled the arm unit out to inspect. Tested the windings on the innards and found variable readings from end to end , middle to end and barely apart. So I know the resistance does vary.
    Turns out under the mag glass the hair thin winding on the end is broken. Time for some micro soldering.

    . 20200303_170628.jpg

  2. #2
    Super Moderator bmorgil's Avatar
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    Maximum respect for fixing the original stuff! I admire your diligence in the trouble shooting. Never say die!

  3. #3
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    I have tried to fix fuel sending units and either had no luck or only worked for a short time. I wish you luck, sounds like you have the patience.

  4. #4
    Super Moderator LarrBeard's Avatar
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    Sending unit repair

    Quote Originally Posted by SeanDo40 View Post
    1949 Willys Jeepster


    Turns out under the mag glass the hair thin winding on the end is broken. Time for some micro soldering.

    . 20200303_170628.jpg
    Peel off a turn of wire to be sure you have enough slack to make the repair. Clean the wire well, you will probably have to use an aggressive solder flux; many of those wirewound units used an almost non solderable
    wire that was actually welded vs. soldered.

  5. #5
    I'm not sure so much effort and time was well spent on an item that will never see the light of day again, at least in my lifetime. But troubleshooting and figuring out the issue was well worth it.

  6. #6
    Super Moderator LarrBeard's Avatar
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    I assume the repair was successful?

    You don't have to explain why you did it around this group. We do a lot of seemingly unnecessary work on our Jeeps for the same reason that dogs do socially unacceptable things in the yard; We can, and it feels really good when we're done.

  7. #7
    It works but I did order a new one from KW just to have more fault tolerance. And also use the dissected one to teach my kids about variable resistors, sending units et al.
    Next is to get going on the sending unit on a 29'DeSoto and stop checking fuel levels with wooden dowels.

  8. #8
    Super Moderator LarrBeard's Avatar
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    If you get desperate, check out Bob's Speedometer; he does exotic fuel senders as well as speedometers

  9. #9
    Here is the "finished" product. In case future guy runs into this issue; I took a single strand of copper from a high gauge wire, soldered it onto the broken tail. Then I wound it around the end and curled and soldered it to the post on the resistor pack. Not too pretty but it gives me a smooth changr of resistance as the arm sweeps across simulating E to F.
    Had this happened in the middle of the resistor I dont think I would have the steady hand or patience to re-wind the whole thing.
    20200305_185342.jpg

  10. #10
    Super Moderator LarrBeard's Avatar
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    Wow! Another McGuyver Award Winner!

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