Fuel Sending Unit Noise from Contacting Tank Wall

[martincom]

The fuel sending unit in my '71 D100 clangs against the tank wall with fuel slosh. I've removed it and bent the arm once already to what I thought would be a centered position. It helped, but it still clangs against the tank wall.

Am I fighting a loosing battle or can I actually get to the point it doesn't clang against the tank wall? Yeah, I'm one of those, rattles and noises drive me crazy.

[PwrWgnDrvr]

Can't u rotate it to be more centered between the walls? Never had that issue in the 40+ yrs of driving these trucks.

[Wildergarten]

Can't u rotate it to be more centered between the walls? Never had that issue in the 40+ yrs of driving these trucks.

I have. Lots, particularly when it's full. But then 90% of my driving is on dirt.

[martincom]

No, it can't be rotated. The tank bung and the sending unit top plate are keyed.

[Wildergarten]

The fuel sending unit in my '71 D100 clangs against the tank wall with fuel slosh. I've removed it and bent the arm once already to what I thought would be a centered position. It helped, but it still clangs against the tank wall.

If I recall correctly, the float is supended on a rod that wraps around it like a C-clip. Is there a difference beween acceleration and braking? If so, you might just bend the float supending rod a little or slide the float forward or aft in the wrap around it.

[martincom]

The float is a brass barrel shape and the rod has a near 360 degree loop that wraps around it. So moving the float on the rod is not an option.

The float will clang against the tank wall whenever the fuel is sloshing for and aft, such as from braking.

The float rod is rather long, probably near 18" and I'm thinking it might just be the rod flexing as the float is caught by the "waves" of the fuel sloshing in the tank.

Before I spent too much time on it, I thought I would check with the group to see if it was even possible to prevent it or if I'd just be chasing my tail.

[martincom]

I pulled the sending unit again and gave the float rod another tweak. It is easy to remove. By aggressively rocking the truck fore/aft, I was able to duplicate the clanging before I altered the rod. I could not afterwards. So we'll see what happens on my next drive.

The first time I had the sending unit out to adjust the rod, I noticed the float would rest on the fuel pickup tube. That seemed odd, as overtime, it would wear a hole through the float when the vehicle was operated or towed with low fuel. So at the same time, I adjusted that so it would not occur.

The second time I adjusted the rod, I also changed it so the gauge would read full with a full tank of fuel.

My bride is becoming jealous of the D100. Since I acquired it in May, she states I spend more time with it than her. There maybe some truth to that....

[Wildergarten]

The float is a brass barrel shape and the rod has a near 360 degree loop that wraps around it.

That's how I recalled it.

So moving the float on the rod is not an option.

I would think one could slide the barrel along its length in the loop.

The float will clang against the tank wall whenever the fuel is sloshing for and aft, such as from braking.

The float rod is rather long, probably near 18" and I'm thinking it might just be the rod flexing as the float is caught by the "waves" of the fuel sloshing in the tank.

There is also slop in the hinge.

[PwrWgnDrvr]

Pretty sure I remember a groove in the brass float that the rod clips into. You could change it to a non metallic float that doesn't "clang" when it hits the tank. Ford used something like that which is a direct fit on the Dodge senders.

[Wildergarten]

Pretty sure I remember a groove in the brass float that the rod clips into. You could change it to a non metallic float that doesn't "clang" when it hits the tank. Ford used something like that which is a direct fit on the Dodge senders.

It shouldn't be too hard to plop down some solder blobs to effectively make a new groove, but with the length of swing in that float arm, I'd bet more could be gained by rotating the assembly using the slop in the notches that align it at the top or simply bending the arm sideways.

[martincom]

I apologize for neglecting to mention that I did explore your suggestion about moving the float position on the arm. The fuel tank sending unit bung opening is toward the front side of the tank. So I would conclude the float was clanging on the front wall of the tank. The float barrel was already positioned as far rearward, on the rod, as possible.

I don't think much would be gained by attempting to twist the sending unit top plate, in the tank bung opening, to one direction or the other, to position the float to avoid clanging on the tank wall. First, there is not much slop there. More importantly, when tightening the lock mechanism, by tapping it with a punch/hammer, the friction between the lock and top plate will move it against the key way stop.

I haven't had the D100 out for a drive since I last adjusted the float arm. So I have nothing to report as of yet.

Thank you for your council and suggestions.

[Red383]

QUOTE: "The second time I adjusted the rod, I also changed it so the gauge would read full with a full tank of fuel."

How did you adjust this? My gauge reads 3/4 tank when I fill it up, I would like to fix this.

Thanks,
Aaron

[Wildergarten]

Thank you for your council and suggestions.

Sorry I couldn't be more certain, it's been 25 years since I've been into that tank.

[martincom]

QUOTE: "The second time I adjusted the rod, I also changed it so the gauge would read full with a full tank of fuel."

How did you adjust this? My gauge reads 3/4 tank when I fill it up, I would like to fix this.

Thanks,
Aaron

1, With a full tank of fuel, disconnect the wring from the sending unit and measured the resistance, with an ohm meter, and record.

2. Remove the sending unit.

3. Lay the sending out on a flat surface, connect the ohm meter and move the float arm for exactly the same resistance reading in step 1. This is the float position with a full tank of fuel.

4. The next step requires a bit of dead reckoning, Measure the distance from a line extended from the same plane of the sending unit top plate to the float.

5. Move the float arm against the "full stop".

6. With the float arm against the full stop, verify the resistance is zero or very near zero. If is is something significantly different, there is an issue with the float rheostat. This is very uncommon.

7. Again with the float arm against the full stop, adjust the arm so the float is in the same position as 3, utilizing the measurement made in step 4 as a reference.

8. Re-install and test.

[Red383]

Thanks for the info. I will give it a try.

Aaron

[martincom]

Well, I didn't totally eliminate the clanging, but I greatly reduced it. I think I have it at the optimum position. I'll only notice it when stopping with a full tank of fuel.

[martincom]

Aaron,

I didn't think of this until yesterday. You may want to check the instrument voltage regulator. If it is running low, all your gauges excluding the amp meter will read low. It is easy to check. Just unplug either the fuel or temp sending unit and meausre the voltage, with the ignition on or accy. It should be 5 volts. At least everything I've had has been 5 volts. If I get a chance, I'll confirm that on my D100.

On my D100, the instrument voltage regulator is integral with the fuel gauge. It has a an output terminal that feeds regulated voltage to the temp gauge and the optional oil pressure gauge.

If it is low, you could look at utilizing an a solid state regulator---IC chip. I did this on my 70 Charger R/T many years ago.

[martincom]

I measured the instrument regulator voltage, on my '71 D100, at the fuel sending lead (with it disconnected from the sending unit), this morning. I forgot they were a low frequency regulator. As such, the voltage will pulse up & down making it impossible to interpret with a digital voltmeter. Using an analog meter, the voltage swung from a about 2.3 volts to 3.7 volts, with the average being about 3.0 vdc ( volts DC).

[Wildergarten]

I measured the instrument regulator voltage, on my '71 D100, at the fuel sending lead (with it disconnected from the sending unit), this morning. I forgot they were a low frequency regulator. As such, the voltage will pulse up & down making it impossible to interpret with a digital voltmeter. Using an analog meter, the voltage swung from a about 2.3 volts to 3.7 volts, with the average being about 3.0 vdc ( volts DC).

Yup, the thermal mass of the bimetal in these gauges functions as an integrator.

[sweatybetty]

My float used to clang also. Reduced it by 90% covering the float with a piece of bicycle inner tube held on with zip ties.