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Brake cylinder crystals

Bill Young

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Healey Friends

How about the chemical experts in our group. We have been changing out brake cylinders at our recent shop meets and find significant corrosion with a build up of some sort of green “growth”crystals. We ask where this comes from and if there is any prevention? Take a look at this picture. Thoughts?
 

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Healey Nut

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I’m no metallurgist or chemical expert but take a look at battery terminals that are not protected , combine that with leaking brake fluid and voila ....greasy green goo .
 

Madflyer

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I would have said salted roads but where you live unless sea air or driving on the beach. Try a spray coat of clear lacquer. And on the side a grounding problem cause Electracies. Madflyer
 
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Good question. Can you correlate with type of BF used; i.e. DoT3 or 4? I had the LMH DoT4 in our BN2 turn to a (greenish) gel after it sat for several years. I replaced it with Pentosin brand--recommended for BMWs and other German cars--and a couple cylinders leaked. Tom Monaco told me to only use Castrol DoT4, so I'll try that next.

DoT3 is mostly ethylene glycol, DoT4 also contains borate esters; boron is a semi-crystalline element that produces a green flame when heated by a torch. If this problem only occurs with DoT4 and not DoT3 I'd strongly suspect the borate esters. Of course, DoT3 was originally spec'd for cars of that era, but DoT4 has a higher boiling point. Note DoT3 is often spec'd for ABS systems, supposedly because it is less likely to aerate/foam as ABS systems can cycle rapidly.

For all the horror stories about DoT5 (silicone) BF, I've been running it in my BJ8 for at least 20 years and never had an issue I can attribute to the fluid. Of course, silicone is made from sand, and crystallization wouldn't be surprising, but I've never seen or heard of it happening.
 

BigGreen

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GregW

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Silicone itself is made up of carbon, hydrogen, oxygen and silicon. Note that the ingredient contained within silicone is spelt differently. The ingredient silicon comes from silica which is derived from sand. ... It's then mixed with the other chemicals to create silicone.
That sounds a lot like Subway's description of their sandwich bread several years ago.
 
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Silicone itself is made up of carbon, hydrogen, oxygen and silicon. Note that the ingredient contained within silicone is spelt differently. The ingredient silicon comes from silica which is derived from sand. ... It's then mixed with the other chemicals to create silicone.

See; https://silicone.co.uk/news/where-does-silicone-rubber-come-from/


I know the difference. It was a bit of a stretch, but because silicone is a compound containing silicon, I speculated that it could crystallize--"crystallization wouldn't be surprising"--though I've not seen it happen. Silicone is great stuff, I use a 'dry silicone' lubricant where a light lubricant is required--e.g. speedometer cables and starter worm gears--as it doesn't seem to attract dirt and gunk-up as much as petroleum-based lubricants and, of course, it has certain, er, 'cosmetic' applications.

I mentioned that I had DoT 4 gel in my BN2, and I'm replacing a wheel cylinder that appears to be crusted with the same sort of substance shown in OP's photo, but dried out. It appears this may be a common problem, and I'd like to figure it out. If the owners all used DoT 4, then the borate esters--I also know the difference between boron* and borate--could be the culprit, since DoT 3 doesn't contain borate esters (presumably, DoT 3 was originally spec'd for our 50s-era cars, but there was a DoT 2). DoT 3 would be sufficient for our street-driven cars, though racers might prefer DoT 4, 5 or 5.1.

* Incidentally, there's a town--actually, a 'census-designated place'--called Boron in California, home to a large open-pit boron mine. You wouldn't want to live there.
 

Healey Nut

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That sounds a lot like Subway's description of their sandwich bread several years ago.

Im thinking with all that silicone it has to parts of Dolly Parton and Kim Kardashians anatomy .
 

Madflyer

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I have been to Boron CA several times there is a great Mexican Food place. It is a little town not to far from California City it is not on the main interstate. A TR 6 friend told me about it so we pulled off. It is a desert town about 20 from no where. As for Boron it self it is a chemical that has a used to clean up Radiation. It was on hand when I worked at a NUK power plant in Sacramento CA.( I do not Glow in the dark ) Madflyer
 

John Turney

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Since it's on the outside of the cylinder, what you are seeing is probably dirt, brake lining dust, bearing grease (front) or oil (rear) and a bit of brake fluid. Old DOT 3/4 fluid does seem to crystallize and attract dirt & dust. Green may be from copper which may be part of the cylinder alloy.

When I rebuilt my brake system 20 years ago, I went to DOT 5 and have never looked back. A couple of years ago, I replaced the "rubber" pieces when I had to replace the pads. My thought was that since the non-brake rubber parts were cracking, I should replace the brake "rubber" parts too. The inside of the cylinders were pristine. "Rubber" is in quotes because it's probably EPDM elastomer.

Switching to DOT 5 requires complete rebuild/replacement of the brake system because it's not compatible with DOT 3, 4, or 5.1.
 
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Bill Young

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Thank you all for your comments..

Cheers
 
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