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Thread Tools | Display Modes |
09-02-2017, 01:02 PM | #1 |
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Join Date: May 2010
Location: Coral Springs FL
Posts: 11,011
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Gas Tank Sending Unit Repair
I have spent the last few days trying to discover why my 40 Ford gas tank sending unit is not working correctly. I have a gauge and the sending unit wired together on the work bench along with the written material on how the fuel gauge and the sending unit work together using the heated bi--metallic strip operating principles. I am using a 6V dry cell as the power source. I can get the gauge needle to register full when the float is all the way down but, that is incorrect. Gauge should register empty. When I raise the float all the way up, gauge still reads full. The little calibrating resistor inside the unit registers 51 ohms when the leads are touching it's surface and 0 ohms when touching the ends of the resistor. I am thinking there must be a way to repair or modify these sending units so they work. Has any Ford barner given it a try? It would be a giant step forward for mankind if a "fix" could be found. I am not an electrical wizard. I have attached photos. Thanks, JIM
Last edited by 19Fordy; 09-02-2017 at 01:35 PM. |
09-02-2017, 01:21 PM | #2 |
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Join Date: Jul 2014
Location: Iowa
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Re: Gas Tank Sending Unit Repair
From the pictures, it seems you have an original "King Seely" sender. They operated by sending pulses to the gauge in proportion to the float level position. To my knowledge, they are difficult or impossible to repair. While the replacement senders use a variable resistor, when properly installed with a carefully calibrated float arm, they are acceptable.
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09-02-2017, 03:05 PM | #3 |
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Join Date: Sep 2016
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Re: Gas Tank Sending Unit Repair
I can't tell from the photos wheter the resistance wire which is wrapped around the bimetalic strip is connected to anything as it looks not to be. Clarify pls. If not, you can spot weld it to the proper post and voila. Spot weld needs only 20-30v and moderate pressure.
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09-02-2017, 03:13 PM | #4 |
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Join Date: Jun 2010
Location: San Antonio, Texas
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Re: Gas Tank Sending Unit Repair
If it registers full scale with little or no pressure on the sender heater arm(bi-metallic), you might check and see if the points are stuck together in the sender between the ground contact and the bi-metallic arm. This will cause the arm to heat up excessively and go to full deflection bend since it can't open the circuit. The gauge just mirrors what ever the arm in the sender does. When the sender float arm is at the empty location it won't deflect the heater arm very much before the points open up. When the float arm is at full, the eccentric action deflects the ground arm to it's full extent which requires a lot more heat to make the bi-metallic arm bend enough more to open the points. If the points are fused, it's just going to deflect to the full extent of it's capability and the gauge will do the same. The bad thing is, that this situation makes the little heater elements work all the time which can burn the coils eventually. Once the coil is bad in a unit, you might as well pitch it. It's that or a person would have to get the correct wire and fabricate a new heating element coil and set of points. A bad bi-metallic arm might do the same if it won't return to its low position when the electrical circuit is disconnected from the battery.
If the circuit is open, it shouldn't work at all. Insure the circuit is connected and properly insulated from shorting to ground. If it is shorted to ground somewhere the the gauge might go to full hot which could give a full indication depending on where the short is in the system. Last edited by rotorwrench; 09-02-2017 at 03:18 PM. |
09-03-2017, 09:45 AM | #5 |
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Join Date: May 2010
Location: Coral Springs FL
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Re: Gas Tank Sending Unit Repair
Thank you all for the info.
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09-03-2017, 10:21 AM | #6 |
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Re: Gas Tank Sending Unit Repair
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09-03-2017, 10:47 AM | #7 |
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Join Date: May 2010
Location: Coral Springs FL
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Re: Gas Tank Sending Unit Repair
Juergen, Thank you for that very helpful "HOW TO" on exactly what to do. I will now give it a try again.
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