The Ford Barn

19Fordy · 09-02-2017, 01:02 PM

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

supereal · 09-02-2017, 01:21 PM

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.

Paul Bennett · 09-02-2017, 03:05 PM

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.

rotorwrench · 09-02-2017, 03:13 PM

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.

19Fordy · 09-03-2017, 09:45 AM

Thank you all for the info.

Juergen · 09-03-2017, 10:21 AM

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In your picture IMG 2451b you will find a toothed wheel. This is the adjusting part of the gauge. Turning it one way increases the tension on the bi metallic strip (taking more on time to break) and the other way to decrease the tension. If I remember right, the points should make/break about 60 times per minute. Measure the resistance of the sending unit from the input to ground without applying voltage. The points should be closed and the resistance low. If the resistance is high either the points are open or the points are corroded (or their is an open in the circuitry). If the points are not corroded, adjust the wheel to close the points. Now with the gauge installed and voltage applied, the points should open (break). If not turn the toothed wheel until it opens. Then adjust the wheel so the gauge reads empty when empty. It may not read full when full if the bi metal has lost some linearity. I adjust for empty because I know when I fill the tank that it is full.

19Fordy · 09-03-2017, 10:47 AM

Juergen, Thank you for that very helpful "HOW TO" on exactly what to do. I will now give it a try again.

09-02-2017, 01:21 PM	#2
supereal Senior Member Join Date: Jul 2014 Location: Iowa Posts: 1,634	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.

09-02-2017, 03:05 PM	#3
Paul Bennett Senior Member Join Date: Sep 2016 Posts: 628	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.

09-02-2017, 03:13 PM	#4
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,453	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
19Fordy Senior Member Join Date: May 2010 Location: Coral Springs FL Posts: 10,965	Re: Gas Tank Sending Unit Repair Thank you all for the info.

09-03-2017, 10:21 AM	#6
Juergen Senior Member Join Date: May 2010 Posts: 503	Re: Gas Tank Sending Unit Repair Sponsored Links (Register now to hide all advertisements) In your picture IMG 2451b you will find a toothed wheel. This is the adjusting part of the gauge. Turning it one way increases the tension on the bi metallic strip (taking more on time to break) and the other way to decrease the tension. If I remember right, the points should make/break about 60 times per minute. Measure the resistance of the sending unit from the input to ground without applying voltage. The points should be closed and the resistance low. If the resistance is high either the points are open or the points are corroded (or their is an open in the circuitry). If the points are not corroded, adjust the wheel to close the points. Now with the gauge installed and voltage applied, the points should open (break). If not turn the toothed wheel until it opens. Then adjust the wheel so the gauge reads empty when empty. It may not read full when full if the bi metal has lost some linearity. I adjust for empty because I know when I fill the tank that it is full.

09-03-2017, 10:47 AM	#7
19Fordy Senior Member Join Date: May 2010 Location: Coral Springs FL Posts: 10,965	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.