More fuel tank sending units

Fuel and Air Systems

  1. steve from staten island

    steve from staten island FBBO Gold Member FBBO Gold Member

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    Ive read the posts recently in the GF and one here the other day. This is a problem im determined to figure out.
    Considering all the wiring is new, the cluster restored and gauges checked and also grounding out unit and fuel gage pegged the only logical explanation was the sending unit. I have two and I also have a original Mopar. No matter the gauge wont register, with 6 gallons it barely comes up to the empty mark, with ten just about to 1/4 tank.
    What I discovered was with the sending unit being held in my hand having jumper wires as I moved the float the gauge worked good. Two floats were brass, one plastic, the float arms all worked freely.
    I can only think the float is not moving properly in the tank.
    I was wondering could I check float operation in a large container of water or would disel fuel be a better option....Or am I incorrect .....Thanks for any and all help/advise
     
  2. BLK 68 R/T

    BLK 68 R/T Well-Known Member

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    I know the biggest problem with the reproduction sending units is the resistor spring inside. Original ones are a tapered spring, smaller on one end and bigger on the other. The repro ones are the same size through the full length. So right there is the main issue, even 1/2 tank won’t register right since the resistance at the halfway point of the spring is different vs an original one.
     
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    • miller

      miller Well-Known Member

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      If your trying to use one of the 'repos', probably a waste of time. Won't say you might get lucky, and get one that reads right. But, as BLK 68 R/T says, the windings in the repos are not like the OEM units.

      Don't know if your that far into it, but on mine, before I installed the fill tube in my tank, I used a wooden rod to check the float arm swing inside the tank. Yes, use one of the brass floats!
      While I 'studied' up on things, it was noted...the sending unit arm/float should not make contact, up or down, with the tank itself.
       
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      • hunt2elk

        hunt2elk FBBO Gold Member FBBO Gold Member

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        And that is the whole problem. Old ones were non linear, and all the new ones are linear. A guy can usually get the full and empty readings kind of close by bending things, but everywhere else in the scale is wacky. Still can't believe nobody has reproduced a quality resister spring.
         
        Last edited: Nov 7, 2019
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        • 69L48Z27

          69L48Z27 FBBO Gold Member FBBO Gold Member

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          I too was determined to get a repop one to work. Tweaking the arm was the only way to get it close. It does seem like an open market for someone to make a quality reproduction.
           
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          • JimKueneman

            JimKueneman FBBO Gold Member FBBO Gold Member

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            The other thing I noticed on my A-Bodies is the length of the arm is MUCH shorter on the replacement which would make it much more sensitive and difficult to get right. Long arm = little move moment on the spring compared to the same amount of fuel change with the short arm.
             
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            • steve from staten island

              steve from staten island FBBO Gold Member FBBO Gold Member

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              My question would be about testing it.....I dont want to fool around with gas in the tank...Id like to have the tank down and run jumper wires, then I could bend the arm if needed. Remove the unit and try another. I would rather not have gas in the tank. Could I use diesel ?
               
            • 66plysat

              66plysat Well-Known Member

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              After reading numerous posts about bad aftermarket sending units a thought came into my head. Obviously cars being manufactured today have working sending units and gauges, could a sending unit and gauge from a 2019 vehicle be modified to fit into our old cars?
              If you took a sending unit from a gas tank of a newer Dodge, Chevy or Ford and put it in a custom made gas tank to fit our old Mopars as well as swapping out a new gas gauge for an old gauge, would it work?
              If that would work, great! If it won't work, why not. My knowledge of car electrical and fuel systems is very limited. I'm sure Mopar owners who want a completely original car would not consider swapping out the fuel system but for those of us who have done modifications to our cars maybe changing a new car system for old might be an answer to the aftermarket sending unit problem.....thoughts?
               
            • furyus

              furyus Well-Known Member

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              There is a product called "Meter Match" it is put in line with the sending unit wire. Plus power, and ground. It lets you set 4 points on the gauge. So I set Empty, 1/4, 3/4, and full. Works way better than just the repop sending unit. Spent a couple years trying to find a stock A body sending unit. So I ended up going with the meter match. Also, try a different instrument voltage regulator. I had a bad one that pegged the gauges.
               
            • steve from staten island

              steve from staten island FBBO Gold Member FBBO Gold Member

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              Meter match as far as I know is for mismatched sending units and gauges. Where Ohm requirements dont match.
              The sending unit I had in the tank, I used jumper wires and while holding it in my hand, moved the arm. It worked very well. So now why doesn't it work in the tank? Seeing that the tank is 18 gallons with 6 gallons in it, the gauge should at least read above empty.
              All I can think of at this point is a bad ground
               
            • furyus

              furyus Well-Known Member

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              There's supposed to be a ground strap that goes from the sending unit to the fuel line. If it's missing, for testing you can make a ground wire from the sending unit to any good ground.
               
            • miller

              miller Well-Known Member

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              Is the sending unit 'repo'??

              The whole system needs to be working, and working right. Yes, a good ground in the system is needed. System means...the sending unit, gauge, and the wiring.

              I had bought one of the repo units for my 64. After testing it, opening the windings to find out why the weird readings, and a damn good laugh...it got shoved back into the box. It's still there.
              I could get full/empty readings on it...but anywhere in between...all over the place. The windings are nothing like the OEM windings. Reading ohms, through the entire range, 'should' be a slow steady sweep, from full to empty.

              As I've said before (maybe I got lucky), I had three OEM sending units. Picked the best parts of each, since each one had some kind of problem. Put together one good unit, correct ohms readings.

              Wiring to the gauge needs to be in good shape. Yes, a good ground from sending unit to the steel fuel line. On my, from looking at my original rusted/bent fuel line, there was a bare steel clamp, the fastened to the body (ground) above the sending unit. It went back on. Makes positive ground from the fuel line to the body/frame.

              Already knew my gauge was good, after testing it. I get complete readings on my gauge...
               
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              • steve from staten island

                steve from staten island FBBO Gold Member FBBO Gold Member

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                Im putting a ground soldered to sending unit, to the body. One of the aftermarket units I have seems to read the best so I'm going to try that one.
                Thanks for all the help
                 
              • steve from staten island

                steve from staten island FBBO Gold Member FBBO Gold Member

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                Hilltop advertises a NOS sending unit for $300. Picture shows unit and it appears to be a exact Chrysler part.
                Brad NOS advertises one and in the picture its shown next to the original box but the unit has a plastic float and a wire that goes from connection to rheostat. He wants $400 !!! 3 to 4 hundred for a 5/16 sending unit really is a lot of money.
                 
              • Daves69

                Daves69 Well-Known Member

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