1957 Gas Gauge won't move past empty

[calbears]

With the ignition on, the gas gauge only slightly moves from pegged on the empty end to about the empty mark. The gauge needle moves about 1/8". There is about 1/2 tank of gas in the gas tank. I checked the gauge by grounding the wire that goes to the sending unit in the tank. The gauge goes immediately to full, so I have read the gas gauge is not the issue. I took the sending unit out of the tank and grounded the unit while still plugged to the wire to the unit. I could manually move the float arm and get an empty reading on the gas gauge at the empty position of the sending unit and about 7/8 full at the full position. I reinstalled the sending unit and again, the gauge just moved from pegged to empty. I then taped the sending unit arm in the full position. I reinstalled it and the gauge shows about 7/8 full. So, the sending unit is grounded okay but it appears the float will not move to register the gas level. I then checked to see if the float would actually float. I put it in a bucket of water and the arm moves as the float floats. As the sending unit did not seem to work properly, I took it apart to see if there was some internal adjustments. Yes and no, but either way, I put it back together and it doesn't really work anymore.

I then bought another sending unit hoping that this would solve the problem. Pretty much the same as above as the gas gauge only slightly moves when the unit is installed. The only difference from the first sending unit is that I have the new unit out of the tank and manually move the float arm to the full position, it will only read about half full. I have read bending the float arm may help but I have not tried that yet as there is no use bending the arm if the gauge will not register with the sending unit installed.

My only thought is to completely fill the gas tank and see what, if anything, happens. It seems futile as there is certainly a fair amount of gas in the tank. Any other suggestions?

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[sre]

You have pretty much covered it all. The only thing I can think of is checking the ground and wire from sending unit to gauge. I would run a new wire from the sending directly to the gauge. Then I would run a ground wire from one of the hold down screws of the sending unit to the back of the gauge.

 

[Ward 57]

I'm sure there are documents on how to bench test your gauge. The biggest problem can you do it while in the dash or have to pull it.

 

[doug7740]

Here is the document that Ward 57 is referring to.

doug7740
1955 Thunderbird Blue

 

[radar]

That’s great advice.
However, I too had the same problem and I found it was a twofold...
1) the replacement sending units are suspect, and Casio was nice enough to replace them no questions asked. 2) the float arm on these replacement is almost twice as long as the original float arm resulting in a longer swing arc. After several head scratches, I cut about half the arm off and it works better-still not perfect. This should be an easy experiment for you since you already have 2 in hand. Please let the forum know if you try this and whether it worked for you. Thanks

 

[Jimpilch]

With the ignition on, the gas gauge only slightly moves from pegged on the empty end to about the empty mark. The gauge needle moves about 1/8". There is about 1/2 tank of gas in the gas tank. I checked the gauge by grounding the wire that goes to the sending unit in the tank. The gauge goes immediately to full, so I have read the gas gauge is not the issue. I took the sending unit out of the tank and grounded the unit while still plugged to the wire to the unit. I could manually move the float arm and get an empty reading on the gas gauge at the empty position of the sending unit and about 7/8 full at the full position. I reinstalled the sending unit and again, the gauge just moved from pegged to empty. I then taped the sending unit arm in the full position. I reinstalled it and the gauge shows about 7/8 full. So, the sending unit is grounded okay but it appears the float will not move to register the gas level. I then checked to see if the float would actually float. I put it in a bucket of water and the arm moves as the float floats. As the sending unit did not seem to work properly, I took it apart to see if there was some internal adjustments. Yes and no, but either way, I put it back together and it doesn't really work anymore.

I then bought another sending unit hoping that this would solve the problem. Pretty much the same as above as the gas gauge only slightly moves when the unit is installed. The only difference from the first sending unit is that I have the new unit out of the tank and manually move the float arm to the full position, it will only read about half full. I have read bending the float arm may help but I have not tried that yet as there is no use bending the arm if the gauge will not register with the sending unit installed.

My only thought is to completely fill the gas tank and see what, if anything, happens. It seems futile as there is certainly a fair amount of gas in the tank. Any other suggestions?

It could be that the variable resistor on the original sender had either a broken wire in the resistor or had a high resistance in the lower part of the contact area. Not all senders have the same resistance, depending on manufacturer, sounds like your new one has a higher resistance than the original.

 

[calbears]

Thank you all. A few thoughts:

1. Checking the gas gauge - I already did the test where I ran a ground wire from the sending unit wire to the car body and the gauge goes to full as it should. This reportedly confirms the gauge works. Additionally, the gauge moves when I manually move the float arm.
2. Running a new temporary wire and a temporary ground wire from the sending unit to the gauge seems like a worthwhile try. I will try that today. In testing the voltage from the gauge to the sending unit, should the wire show 12V at the sending unit? I will have to recheck this but I checked it several days ago and I remember it only showed about 5V. Maybe there is not enough voltage to move the float arm. I’m no electrician so does that even make sense?
3. Both the variable resistance and lack of unit quality theories both sound good. However, two different sending units pretty much acted the same way making these theories still possible but seemingly not as probable. I already told the manager at the parts store how the first sending unit reacted. If I tell him the one I just bought from him acted the same way there is not much chance he will swap it for another new one.

Any further thoughts are appreciated, especially any thoughts about whether there should be 12V to the sending unit.

 

[calbears]

Additionally, if the sending units I have have a higher resistance than the original, what can be done to fix that problem?

 

[fasteddy]

You have checked everything and ensure a good ground. There is a resistor mounted above the speedometer in the dash. It reduces the voltage from 12 bolts to 8 volts. When operating it provides a stable voltage to all gauges. When operating, you will notice the gas gauge needle will pulse when reading the fuel level.
This corrected my problem after completing all the steps you have described. Good luck.

 

[sre]

That little rectangular part is the constant voltage regulator. It should have a good ground. It is connected to the fuel gauge and the temperature gauge. If both of those gauges read low that could be your problem. According to the Ford manual voltage should read between 0-10 volts. If you have a Ford Manual there is good information on tests to run on the gauge circuit.

 

[calbears]

You have checked everything and ensure a good ground. There is a resistor mounted above the speedometer in the dash. It reduces the voltage from 12 bolts to 8 volts. When operating it provides a stable voltage to all gauges. When operating, you will notice the gas gauge needle will pulse when reading the fuel level.
This corrected my problem after completing all the steps you have described. Good luck.

Just to clarify, the voltage at the sending unit should be 8V? I rechecked the voltage to the sending unit. The meter needle continuously jumps back and forth between zero and 25V. That sure doesn’t sound right. Do you think if I replaced this resistor it might stabilize the voltage and hopefully the 8V would move the float arm? If so, how difficult is it to replace the resistor? Thank you for the information.

 

[calbears]

That little rectangular part is the constant voltage regulator. It should have a good ground. It is connected to the fuel gauge and the temperature gauge. If both of those gauges read low that could be your problem. According to the Ford manual voltage should read between 0-10 volts. If you have a Ford Manual there is good information on tests to run on the gauge circuit.

When you refer to the “little rectangular part,” is that the resistor fasteddy spoke of in his post?

 

[sre]

Yes that is the constant voltage regulator. I'm 6'4" 300lb I had to remove the seat to get under the dash. It is not the easist thing to change.

 

[calbears]

Online they call this an instrument voltage regulator. Is this the part? At 5’11”, 165, hopefully I can get in there. Ha-ha!

 

[sre]

Yes that's it. 1st thing disconnect neg. terminal of battery. I made a ground wire that I installed at the time I installed the part. The one you remove (if it's original) will have 2 screws holding it on. Good luck.

 

[Ward 57]

Yes that's it. 1st thing disconnect neg. terminal of battery. I made a ground wire that I installed at the time I installed the part. The one you remove (if it's original) will have 2 screws holding it on. Good luck.

Are reproduction original style gauge regulators even available? Relays and circuit breakers, yes. Just checked the major suppliers and couldn't find it.

 

[sre]

I don't think the original design is available. The better new ones are solid state. I recently had to put one in my 68 Mustang, it is the same one. I don't think it would be economical to make all applications.

 

[fasteddy]

View attachment 25913
Online they call this an instrument voltage regulator. Is this the part? At 5’11”, 165, hopefully I can get in there. Ha-

Are reproduction original style gauge regulators even available? Relays and circuit breakers, yes. Just checked the major suppliers and couldn't find it.

Call Birds Nest in Oregon (971)233-9000
Great technical support and no sales tax!!!

 

[Ward 57]

Call Birds Nest in Oregon (971)233-9000
Great technical support and no sales tax!!!

I thought they catered to the bigger birds but if the system was still in effect Quite relevant.

 

[fasteddy]

I thought they catered to the bigger birds but if the system was still in effect Quite relevant.

Got our sending unit & stabilizer from them for a 62 bird. Give them a call.