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Does float arm length matter on the fuel sending unit?
Hello so a little background my 2002 7.3 short bed is sucking in air from what I think is a loose compression fitting on the sending unit (hutch mod is already done no pickup foot) but unfortunately on my sending unit one of the ground wires broke off and it looks like it can’t be fixed. So I went out and bought an oem sending unit off some guy on Facebook for 25 bucks and was gonna do the hutch mod to that one. But after getting it home I noticed the float level arm is noticeably longer than the original one. Perhaps the new one I got was in a bigger tank? The short one measures around 9.5 inches and the long one measures 12.5. Did both measurements from the float to that 90 degree bend on the arm. Does this difference in length matter at all? Will it cause a false reading? My theory was the float will only go as high as the fuel level is so it shouldn’t matter. Unless I’m wrong. Feedback will be greatly appreciated.
Pics for reference.
You'd have to do some trigonometry to calculate it out, but I Imagine the full and empty will be the same, the middle may vary slighty from factory, but longer arm may have more resolution. Assuming it fits...
The float arms can be swapped from one unit to the other provided they are the same diameter rod. Also it is possible to repair the broken wire on your original sender. There are 2-3 tabs holding the plastic body to the metal backing plate. You can gently pry those tabs with a small screwdriver to release the sensor. Once inside you'll see the factory wire was simply soldered to the board of the variable resistor. So it just needs to be resoldered to be good as new. Solder paste is your friend on that job.
Edit: To answer your question, yes the arm length does effect the accuracy of the sender measurement. A shorter arm will register full before the tank is actually full and the same for empty. The rod length is essentially the radius of what would be a circle. The shorter radius would reach the upper limit at a lower fluid level than the longer would.
The float arms can be swapped from one unit to the other provided they are the same diameter rod. Also it is possible to repair the broken wire on your original sender. There are 2-3 tabs holding the plastic body to the metal backing plate. You can gently pry those tabs with a small screwdriver to release the sensor. Once inside you'll see the factory wire was simply soldered to the board of the variable resistor. So it just needs to be resoldered to be good as new. Solder paste is your friend on that job.
Edit: To answer your question, yes the arm length does effect the accuracy of the sender measurement. A shorter arm will register full before the tank is actually full and the same for empty. The rod length is essentially the radius of what would be a circle. The shorter radius would reach the upper limit at a lower fluid level than the longer would.
okay thanks. I’ll go ahead and repair that wire then.
Hey I was wondering does anyone know where you can still get a 7.3 factory pickup sending unit because I have a 7.3 that has a bad float switch and always reads full
And does it matter if it is a factory switch because there is ones on Amazon that I'm seeing that I think could work and I'm just unsure
Last edited by 26camacho; Apr 30, 2025 at 01:13 AM.
Hey I was wondering does anyone know where you can still get a 7.3 factory pickup sending unit because I have a 7.3 that has a bad float switch and always reads full
And does it matter if it is a factory switch because there is ones on Amazon that I'm seeing that I think could work and I'm just unsure
1st, you did not give us enough information, to know what truck you have?
an Excursion like mine, with a 44 gallon tank?
or a pickup with an extended tank, or factory tank?
The float must be able to reach the top of the tank, so I would think the "arm length" would make a difference.
Likewise, it needs to be able to rest on the bottom of the tank, or nearly so.
I have a habit now, of planning my next fuel stop at half a tank, or 300 miles... back when my fuel gauge on a truck was kaput, I used the GPS Trip Meter to note how far I had gone, since the last fillup...
but , if you forget to reset that Trip Meter, well, gulp, you might run out of gas
Hey I was wondering does anyone know where you can still get a 7.3 factory pickup sending unit because I have a 7.3 that has a bad float switch and always reads full
And does it matter if it is a factory switch because there is ones on Amazon that I'm seeing that I think could work and I'm just unsure
Originally Posted by udsuth78
The float arms can be swapped from one unit to the other provided they are the same diameter rod. Also it is possible to repair the broken wire on your original sender. There are 2-3 tabs holding the plastic body to the metal backing plate. You can gently pry those tabs with a small screwdriver to release the sensor. Once inside you'll see the factory wire was simply soldered to the board of the variable resistor. So it just needs to be resoldered to be good as new. Solder paste is your friend on that job.
Edit: To answer your question, yes the arm length does effect the accuracy of the sender measurement. A shorter arm will register full before the tank is actually full and the same for empty. The rod length is essentially the radius of what would be a circle. The shorter radius would reach the upper limit at a lower fluid level than the longer would.
1st, you did not give us enough information, to know what truck you have?
an Excursion like mine, with a 44 gallon tank?
or a pickup with an extended tank, or factory tank?
The float must be able to reach the top of the tank, so I would think the "arm length" would make a difference.
Likewise, it needs to be able to rest on the bottom of the tank, or nearly so.
I have a habit now, of planning my next fuel stop at half a tank, or 300 miles... back when my fuel gauge on a truck was kaput, I used the GPS Trip Meter to note how far I had gone, since the last fillup...
but , if you forget to reset that Trip Meter, well, gulp, you might run out of gas
The truck used a 2001 Ford F-350 with a 7.3 diesel in it the fact I was wondering if the ECM is particular about having a factory float switch in it or does it not matter and you can go by an aftermarket one and if I remember correctly it's either a 60 gallon tank or a 65 gallon tank
The float is just a variable resistor, not unlike a potentiometer. The only thing that matters as far as the signal sent to the gauge cluster is the resistance value and orientation. If I'm remembering correctly it is 15--165 ohms with 15 being empty and 165 being full. Which is why it reads full when it loses connection. Last thing the wire can be broken anywhere in the circuit . It is more often at the sensor but not always. You might check everything outside the tank first just in case.
Before putting either unit in put an ohmmeter on it and see if it reads good and clean through the whole sweep. If the only difference is the arm just swap them. I popped mine off while doing the Hutch mod so it didn't get damaged.
New sending units are available from Rock Auto and Amazon. I believe on Rock they are listed as fuel hangers, don't ask me look it up.
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