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Old 09-22-2018, 01:27 AM   #1
Mike_The_Grad
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Science and stuff...

I just replaced the 5 year old LMC fuel sending unit in my 1972 c10 with tank behind seat in cab. The LMC unit's pivot rivet holding the float arm to the electrical pickup broke. So in went a new unit from Brothers truck parts. It worked fine for about a week then the fuel gauge has stopped working again. Verified everything is fine except the float. It seems like it's got a leak. Emailed Brothers and just received a new float. But before I install it I'm gonna submerge it in boiling water to check for leaks. All this seems standard procedure for an aftermarket unit with a bad float.

Now to my "Science theory". This new brothers unit seems to be chromed rather than stainless steel like the LMC unit I had installed about 5 years ago. I will verify this with a simple magnet test. Yes some stainless is magnetic but not usually thinner forms like tubing and sheet metal. Dependent upon its chromium content. Anyways, the float is brass, the tank is galvanized steel and the sending unit is either stainless or chromed steel. The sending unit is sealed with a rubber o-ring. The sending unit has a copper strap that is connecting the 3/8" fuel supply line to the 1/4 fuel return line. My LMC unit did not have this copper strap. Now, I may be wrong here but isnt the electroplating process achieved by placing 2 slightly dissimilar metals into a sort of briny solution with a low voltage charge applied to the dissimilar metals to enable electron dispositioning? Like in "Chroming" bumpers, and the like.
What I'm getting at is, is it possible that because of the nonferrous brass float soldered with nonferrous "leaded or low-lead" solder submerged in gasoline attached to a "chromed" or Stainless Steel float arm and supplied with a lower than 12Volt electrical charge that the Electroplating process is occurring and the "Sacrificial annode"(the floats solder joint material in this case) is merely doing its job based upon its environment and condition?

If my theory is true, then that would explain all of the "bad aftermarket sending unit floats". They just need more solder applied (which may only delay the inevitable) or the electrical charge needs to be eliminated (we know this cant happen). Kind of seems like theres no solution other than a plastic float substitute. But why is that the only viable way around this problem if GM produced these trucks this way with no issues?

And yes, hindsight being 20/20 I regret not saving the float from the LMC sending unit that was fine. But even that unit showed signs of chemical degradation. The black band that coats the pick up signal wire was eaten away and soft like oil soaked rubber gloves.

Thoughts, opinions, or am I overthinking and just not recognizing that QC on overseas items is a term that is used subjectively?
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Old 09-22-2018, 01:49 AM   #2
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Re: Science and stuff...

This is from Wikipedia regarding the electroplating process. I haven't found any mention to if gasoline can be utilized as a solution for the process though.
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Old 09-22-2018, 11:04 AM   #3
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Re: Science and stuff...

Gasoline is such a poor conductor of electricity that I doubt galvanic corrosion is going to be an issue. The original float in my truck sprung a leak, but I happened to have a float out of my '68 Skylark that was plastic, and I used that.
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Old 09-22-2018, 11:33 AM   #4
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Re: Science and stuff...

I'm thinking the problem may be just not enough solder is used to seal the float, and it will probably last for years if soldered better. If you want yours to last forever you could probably solder it and then give it a coat of POR15 paint, which would be quite permanent and seal it against any chemical reaction. If you haven't used POR15 before, I recommend getting a $20 POR15 starter kit and play with it. It is the weirdest paint-like substance I have seen. Don't get it on your hands or on anything you don't want painted.
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Old 09-22-2018, 01:52 PM   #5
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Re: Science and stuff...

You know djmlambert, that is exactly what I had in mind. I bought one of those Por-15 $20 kits about 10 years ago to coat my battery tray. Well I never got around to it and it sat there unopened. I restored the heater box in my 72 c10 and all of the metal parts inside the box had heavy rust set in so I figured it was the perfect chance to try out the por-15 kit. Even after all those years sitting in the garage unopened the product was unaffected. And that little kit goes a LONG way. I was able to cover everything in the heater box, the battery tray in my dads 64 c10, a portion of the inner fender under the battery tray, my bench vise,a bunch of small metal brackets, and I still had some left over! You are correct about getting that stuff on yourself or anything else you dont want it on. It's on there so accept it. Lol.

I pulled the sending unit lastnight and sure enough the float was full of gas. I filled a bowl with 155 water and submerged the new float in the water for about five minutes, no bubbles and I couldn't hear any water swishing around in it so I went ahead and installed it. Gas Gauge works as it should now. Time will tell how long that'll be.
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Old 09-22-2018, 07:54 PM   #6
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Re: Science and stuff...

Its not the chrome in stainless that is magnetic, it is the ferritic component of the alloy that is magnetic.

I bought a tank and sender for my 72 replaced the crap float with a plastic on from (rock auto) a jeep. threw away the old one, paid shipping(more than the float itself) on the new one, paid for the new one. all that to ensure it worked, sold the truck befor it was all done but no need to test and trouble shoot, just replace it and forget it.

fuel only needs to conduct electricity not efficiently to initiate the process. Thats the reason why everything in site in grounded when refueling aircraft. fuel conducts electricity. some senders measure the resistance to conducting electricity between two probes to read fuel levels. So fuel does conduct electricity.
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Old 09-22-2018, 08:56 PM   #7
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Re: Science and stuff...

Don't waste time with the brass float. Replace it with this and never worry about it again...

http://67-72chevytrucks.com/vboard/s...d.php?t=666161

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Old 09-22-2018, 09:42 PM   #8
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Re: Science and stuff...

Mike16, what you say is true regarding the chromium in stainless steel. It is not the chromium that is magnetic. But the amount of chromium and whether or not Nickel is added is what makes stainless steel magnetic. Ferritic Stainless steel has a high chromium content but maintains its magnetism, whereas austenitic stainless steel is not magnetic and usually contains Nickel. I learned all about metallurgy while completing the Welding Technology Program at Ventura Community College. I'm glad to see someone understand where I'm coming from and actually reads someone's post before replying.

71meangreenc10,
That is awesome and I wish I had known about that beforehand. If this one fails on me I'm ordering that plastic one. Thanks. That's going into my bookmarks for future reference.
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Old 09-22-2018, 10:34 PM   #9
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Re: Science and stuff...

No need to get over complicated with science. Those floats are pure crap and the best way to fix them is with a trash can. Smitty already gave the solution.
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Old 09-22-2018, 11:05 PM   #10
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Re: Science and stuff...

300 series stainless has a high chromium content, which renders the magnetic moment small enough as to be negligible. 400 series stainless has less chromium and as a result is more attracted to a magnet, and will in fact corrode. 300 series stainless does not corrode beyond a boundary layer at the surface of the alloy because of the face-centered cubic structure carrying a layer of oxidized material which does not allow oxygen to penetrate further into the crystalline structure. That's why bumpers are chrome plated.

Nickel is a ferromagnetic metal, and as such is attracted to a magnet just like iron is. Don't take a nickel coin out of your pocket and try a magnet on it, because it is an alloy of copper and nickel, so it's just as much non-magnetic as 300 series stainless. Pure nickel metal is attracted to a magnet just like iron.

If fuel conducted electricity, there wouldn't have to be grounds installed all over the place. The fact that hydrocarbons in general are non-conductors is what drives the requirement for ground straps everywhere, not that it conducts. That's just nonsense. The flow of hydrocarbons generates static electricity precisely because it is a non-conductor. Else why would we be told to ground a container when we fill it at the gas station?
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Old 09-23-2018, 04:00 PM   #11
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Re: Science and stuff...

credit goes to smitty. he was the one who advised me to do the floate switch too.

I love science, it raises the bar for all. except the one at the bar.....
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Old 09-25-2018, 09:40 AM   #12
Mike_The_Grad
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Re: Science and stuff...

I appreciate all who have replied and I'm happy to see that there are people who are not afraid to show their intelligence. Hanging around this website for as long as I have, I knew this thread was apt to go in any direction. And while yes Smitty has what seems to be the end all solution to this rather annoying problem, others have read my post and decided to entertain my theory and provided their input. Just as I stated above, I appreciate all who have replied. It's why I love this website.
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