A puzzling problem

[58Yeoman]

A year or so ago, I replaced the original fuel gauge sending unit in my 58 Chevy. Last summer/early fall, it died again. I bought another off ebay and installed it. What had happened to my first one was that the brass float developed 3 large cracks. I installed the new one in Sept. of last year, and now it's done the same thing. It literally blew a square hole in it.

I had soldered up the cracks in the first one and kept it in the drawer, as the unit still worked. I have since bought a modified float off ebay that is a brass end with a different float material for the other half. I have also sent pix to the ebay seller asking if he has had this problem before (it's warranted for 10 years).

I'm just totally perplexed what is causing this problem. I use premium non ethanol gas in both my old cars, with Stabil added and Instead O Lead in both also. Luckily, this cars' tank has a drain plug, and I've installed a petcock until I get this resolved. It takes longer to drain, but it's much less messy.

Any ideas from the great minds on GJ?

 

[The Cobbler]

I'm guessing the brass is too thin, stressed from the roll form and with expansion & contraction inside from heat/cooling, it stress cracks

 

[engineer2]

For something that old, I would buy a replacement float. Google gas tank floats. You can get brass or plastic.
Brass can work harden and it's not that thick to begin with. Does the float always fail in the same orientation? Is it hitting the top or bottom of an full or empty gas tank?
Brass can be affected by some chemicals, particularly anything containing ammonia or sulfur compounds (unlikely in a gas tank).

 

[58Yeoman]

Both floats were brand new when installed, as were the sending units. I never thought to save the original float that was still good, but the sending unit died. The tanks are always full. Last month, I looked at the gas gauge and thought that I had forgotten to fill the tank the last time I drove it. Went uptown to fill it and it took 3 gallons, but was showing MT. That's when I figured the new float wasn't floating any longer.

I may just install the "old" unit with the new float. I just want to hear from the seller first.

 

[HotrodHR]

My guess is you have a dissimilar metals corrosion problem, weakens the float leads to cracking and failure. Try adding a ground from the sending unit to the chassis. Or isolate the float from the steel rod maybe slide a piece of fuel hose or shrink (electrical) tubing onto the steel rod (not sure how the shrink tubing will perform in fuel), or just find a plastic float.

You would think that if the new units were built like the originals that you would not have these problems. The oddest things can cause crazy problems.

Case in point, a friend rebuilt the engine in a 1969 Pontiac reinstalled everything and his floor shifted automatic trans cable kept breaking. After the second snapped cable he asked a mechanic at the dealership for advice (this was in the early '70s). When he told the mechanic that he had just rebuilt the engine the mechanic knew exactly what theproblem was - he failed to install the small grounding strap from the engine to the body when he put everything back together. He went installed the new trans cable and the grounding strap problem solved.