The Ford Barn

Veeder · 12-21-2021, 07:01 AM

I'm being a bit lazy hoping someone knows this off the top of their head otherwise I'll get under the dash.

Looking for the fixed resistance of a ford fuel gauge 1940's vintage

koates · 12-21-2021, 07:29 AM

Not sure what you mean here, do you mean the resistance value range empty to full. Are you trying to match up a modern sender unit to your original Ford gauge ? If that is your intention then that is not how these original Ford gauges work with a variable resistance sender unit. Please explain. Regards, Kevin.

Veeder · 12-21-2021, 07:42 AM

I think Kevin there is a current limiting resistor in the gauge itself. I'm aware (thanks to a few here on the barn ) how the gauge works it's basically a form of pulse width modulation.

To answer your question though I'm a tempting to simulate this on my bench without pulling the gauge out. I'm replacing the tank and have a new sending unit (purely resistive design) and want to see how it behaves as best I can.

And if course finding a new tank that will accommodate the old gauge is not quite as simple as one would hope. I can fit the old gauge into the new tank with an adapter plate but I don't believe the original float will fit.

Bob

19Fordy · 12-21-2021, 10:17 AM

Veeder Here's what the inside of the 1940 Ford gas gauge looks like. 41 is the same.: Gas tank sending unit also shown. Do a search on Gas Tank Sending Unit and tons of great info. appears that will help you. Please report back as to whether or not you are able to get your gas gauge to read accurately at E, 1/4.1/2 ,3/4 and F. Accuracy is the BIG problem as the OEM gauge and sending unit don't operate on the Ohms principle.

rotorwrench · 12-21-2021, 11:10 AM

King Seeley made automotive temperature, fluid quantity, and pressure gauge & indicating systems for a number of manufacturers back in the 6-volt and early 12-volt era. They have a heating coil and a bi-metallic breaker unit in the sender and just a heater & bi-metallic strip in the indicator unit. They work off deflection of the sender by either pressure or temperature methods. For pressure & quantity senders the bi-metallic has pressure acting on it through a diaphragm. For temperature, it only needs a rise or drop in temperature to affect a bi-metallic strip. The breaker sends a variable current to the indicator which reacts to the current sent for an indicator needle movement.

This system has less chance for wear and electrical open or short condition than a resistance type potentiometer movement so it makes it more reliable. Many of the senders just need the points to be cleaned to restore function.

Checking ohms only measures the value of the heating element if anything at all.

19Fordy · 12-21-2021, 12:27 PM

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THANK YOU "rotorwrench" for the clarification. Another thought:
It would be possible to enlarge the hole in the reproduction steel tank so as to acccomodate the stock sender. I did the same with a TANKS INC. plastic tank and was able to use the stock 1940 sending unit.

12-21-2021, 07:01 AM	#1
Veeder Senior Member Join Date: Dec 2012 Location: CT Posts: 394	41 fuel gauge (fixed resistance value) I'm being a bit lazy hoping someone knows this off the top of their head otherwise I'll get under the dash. Looking for the fixed resistance of a ford fuel gauge 1940's vintage

12-21-2021, 07:29 AM	#2
koates Senior Member Join Date: May 2010 Location: Melbourne Australia. Posts: 2,078	Re: 41 fuel gauge (fixed resistance value) Not sure what you mean here, do you mean the resistance value range empty to full. Are you trying to match up a modern sender unit to your original Ford gauge ? If that is your intention then that is not how these original Ford gauges work with a variable resistance sender unit. Please explain. Regards, Kevin.

12-21-2021, 07:42 AM	#3
Veeder Senior Member Join Date: Dec 2012 Location: CT Posts: 394	Re: 41 fuel gauge (fixed resistance value) I think Kevin there is a current limiting resistor in the gauge itself. I'm aware (thanks to a few here on the barn ) how the gauge works it's basically a form of pulse width modulation. To answer your question though I'm a tempting to simulate this on my bench without pulling the gauge out. I'm replacing the tank and have a new sending unit (purely resistive design) and want to see how it behaves as best I can. And if course finding a new tank that will accommodate the old gauge is not quite as simple as one would hope. I can fit the old gauge into the new tank with an adapter plate but I don't believe the original float will fit. Bob

12-21-2021, 11:10 AM	#5
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,422	Re: 41 fuel gauge (fixed resistance value) King Seeley made automotive temperature, fluid quantity, and pressure gauge & indicating systems for a number of manufacturers back in the 6-volt and early 12-volt era. They have a heating coil and a bi-metallic breaker unit in the sender and just a heater & bi-metallic strip in the indicator unit. They work off deflection of the sender by either pressure or temperature methods. For pressure & quantity senders the bi-metallic has pressure acting on it through a diaphragm. For temperature, it only needs a rise or drop in temperature to affect a bi-metallic strip. The breaker sends a variable current to the indicator which reacts to the current sent for an indicator needle movement. This system has less chance for wear and electrical open or short condition than a resistance type potentiometer movement so it makes it more reliable. Many of the senders just need the points to be cleaned to restore function. Checking ohms only measures the value of the heating element if anything at all.

12-21-2021, 12:27 PM	#6
19Fordy Senior Member Join Date: May 2010 Location: Coral Springs FL Posts: 10,923	Re: 41 fuel gauge (fixed resistance value) Sponsored Links (Register now to hide all advertisements) THANK YOU "rotorwrench" for the clarification. Another thought: It would be possible to enlarge the hole in the reproduction steel tank so as to acccomodate the stock sender. I did the same with a TANKS INC. plastic tank and was able to use the stock 1940 sending unit.