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1940 Dodge D-14 Fuel Gauge help needed!


OJD 1972

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I have a question for the forum relating to the fuel gauge for my 40 Dodge D-14 Business Coupe. I have been on a mission to fix the non-working fuel gauge system. I've replaced the sending unit, new wires from front to back and a NOS gauge. The original gauge has this removable card like piece that had three holes that line up with the studs on the back of the gauge and has very small copper wires that wrap around the entire piece. The gauge will not function without it, but it is somewhat deteriorated. Does anyone know what this piece is called or part number? Can it be replaced?  

 

I've also followed the instructions in the shop manual to calibrate the new gauge, but the gauge will not read pass 1/2 tank even with the right arm moved all the way to its maximum point? could the above piece cause the gauge not to operate properly? 

 

The photos attached are the piece in question.

 

Thanks in advance for information related to my questions. 

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If you have a radio that part maybe needed. The piece in question is part of a Radio Fuel Gauge Filter Assembly. The important part of the piece is missing, the condensor or capacitor, depending on which one was used. Its to help suppress radio noise from the fuel gauge and is not doing anything anymore with most of the circuit missing. I would remove whats left of it.

 

My car did not come with a radio and have been trying to figure out what parts are needed to install the factory radio. I do not know what part number your filter is, but I have 3 part numbers for Chrysler Radio Filters: 938904, 1233691, & 1571839. They are not list separately in the parts books, just part of a kit.

 

The 1233691 has a capacitor and is the one pictured below. The number and pictures came from @Dodgeb4ya with many thanks! The 1233691's are for 1946-1948 vehicles. 

 

The number 1571839 has a capacitor is supposed to be for 1954-1956 6v vehicles, but '56 are 12v.

 

The 938904 has a condensor is listed in the parts list for the 802 model radio install kit.

 

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Edited by ccudahy
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I've tried removing it from the gauge and re-hooked it up but the gauge will not function without it. 

 

Any suggestions how to setup the gauge without it to work properly? All NOS gauges I've seen on eBay or other sites do not have or come with this piece.

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Check you wires, The top left stud (#1) should have a blue wire from the #1 terminal on the sending unit from the gas tank. The top right stud (#2) should have a black/yellow or brown/yellow tracer wire from the #2 terminal on the sending unit. The middle bottom terminal (SW) should be a wire from you ignition switch and other the wires that were connected to the gas gauge. From the diagaram looks like a red wire to the wiper switch. Make sure that the bottom stud is not spinning when tightening or damage to the gauge can occur. Following the radio suppression instructions in reverse.

 

After everthing is checked. Maybe, just a guess. The brass rivet, in the middle between terminals #1 and #2, on back of the gauge needs to be grounded. Now that the radio filter is gone.

 

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Edited by ccudahy
Added wire diagram and back of gauge.
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The D14 fuel gauge is of the heated filament type and not moving coil like the simpler GM type. Motors Auto Repair Manual describes the operation of this relatively complex fuel gauge movement in detail and how it relates to sending unit impedance based on fuel level.  They also have a calibration procedure for this unit. This is essential reading to understand how this un conventional gauge set up works. M

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Edited by Marcel Backs
Few pix
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Thank you all for your input and information that have provided to help me solve my issue. 

 

After hooking a ground lead to the brass rivet between the #1 and #2 lugs that did not make the gauge function. I placed the filter back on and and checked the brass rivet with a voltage meter. The meter read 3.5 volts, so I determined its not a ground but the actual hot side of the gauge. 

 

In the picture attached I took a piece of cooper wire and made a small jump wire from the SW lug into the brass rivet. This fix made the gauge function correctly when I bench tested it with a new sending unit and new wiring. I completed the above mentioned calibration procedure and it functioned perfectly. Put it back in the car and it read 1/2 tank when I turned on the ignition switch. The take had approximately half tank. Drove the car for about half an hour and the entire drive the gauge moved towards 1/4 tank. Parked the car turned off ignition and the gauge went to empty. Turned ignition back on and gauge went back to 1/2 tank. 

 

I'll continue my quest to make the gauge operate properly.   

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How long did you wait before you turned the car off again when it read 1/2 a tank? Remember these gauges need time to warm up. They don't read instantly like a modern gas gauge like @Marcel Backs stated above.

Edited by ccudahy
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It took a few minutes for it to cool off before it went all the back to empty. Once it was reading empty I turned the ignition back on where it went back to 1/2.

 

I'm wondering it the air circulating around under the dash could be causing it to read erratic? Because the calibration instructions says to perform the procedure either in a small room with no air circulation or warp something around the gauge to prevent air movement.  

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If it worked on the bench with jumpers, then when using the car’s wiring it malfunctions, this is indicative of a problem with the car’s stock wiring for that circuit. OR One side of the gauge has a bad heater circuit or dirty point contact. M

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