Brake bleeding problems - silicone fluid

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mgcjag
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#41 Re: Brake bleeding problems - silicone fluid

Post by mgcjag » Thu Apr 19, 2018 4:48 pm

I dont see any argument with one side trying to prove the other wrong.....its simply a matter of choice.....but to make an informed decision you need as many facts as possible....thats what the forum is about.....all the posts here will hopefully still be available long after most of us have gone.........Steve
Steve
1969 S2 2+2 & Building a C type replica

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Hugo
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#42 Re: Brake bleeding problems - silicone fluid

Post by Hugo » Thu Apr 19, 2018 5:07 pm

Well, so you say - but when I described the situation I had experienced with a hydraulic throttle on a bus - that it started leaking when I switched to silicone fluid & then gradually stopped again when I topped it up with the old stuff - Angus replied that this was "utter rubbish". I invited him to expand on that claim, but he never did.
Then Peter Crespin averred that what I had done was both dangerous and illegal. If I had been playing with the horizontal stabilizer on a 747 maybe, but this was the throttle on an old bus. I was fully intending to replace the seals, but once it stopped leaking I could see little point.
Neither of these contributions, in my view, added much to the sum of human knowledge.
I have read the attached article, and while it is very thorough, is rather defensive in my view. The author doesn't say much in favor of silicone fluid, except that you can drink it. Ok, it doesn't absorb water, but it can absorb air, which is not much of an improvement if you ask me.
Of particular concern is the question of whether, since it is made from sand, it reverts to that state when sucked into an internal combustion engine. The author makes the quite reasonable point that it would be difficult for an E Type, due to the labyrinthine plumbing of its brake system, to ingest its brake fluid.
But cars do drink their brake fluid from time to time. I remember an Aston pouring out smoke and smelling as though it were running on Castrol R when this happened.
I am still unclear what would happen if a car engine ingested silicone fluid, and frankly I don't want to find out the hard way.
One thing I did learn from the article was the origin of the 'E-Type' designation, which I found interesting.
Hugo Miller - rebuilding an imported Series II OTS & converting to RHD

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johnetype
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#43 Re: Brake bleeding problems - silicone fluid

Post by johnetype » Thu Apr 19, 2018 11:31 pm

What I take from reading as much as I can on the topic and many years of personal experience is that if you take a brand new clean brake system throughout and use DOT 5 silicone fluid it will work fine and you will reap the benefit of a fluid that doesn't absorb water whenever it can and won't ruin your paintwork. For those reasons people who use DOT 5 silicone find it satisfactory and swear by it.

If you have a mixed system of old and new brake components or an old system where you've tried to flush out DOT 3 or DOT 4 fluid before transferring to DOT 5 silicone you may encounter problems. The challenge here is that you may have encountered problems whichever fluid you used as there's no double blind isolation so it's very difficult to know if DOT 5 silicone was the problem or not.

Personally, the despair that results from damaged paintwork from a leak you failed to wash off in time or the inconvenience of replacing a brake cylinder that's rusted solid on a little used car is enough for me to try using the (more expensive) DOT 5 silicone fluid whenever one of my cars has a completely new braking system.

For whatever reason it does appear to be a particularly polarised debate and therefore I don't put much credence into scare stories such as "if silicone fluid gets ingested into our engines it turns to sand" because (a) is it true? (b) our engines eat a whole range of chemicals over their lifetime including sand and cope and finally (c) how likely is that to ever happen? Ask anyone who's engine has a rubber toothed camshaft belt and you know the meaning of Russian roulette at the ends of the risk envelope.

Ultimately, each of us has to weigh the facts as we perceive them and make our own choice; debate doesn't really help here.
John

1969 Series 2 FHC

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#44 Re: Brake bleeding problems - silicone fluid

Post by Hugo » Fri Apr 20, 2018 1:24 am

Engines ingesting brake fluid does happen occasionally. I've seen it happen a few times. As for the 'sand' theory, I have no idea, and as I said, I don't intend to find out.
I'm not sure that traditional brake fluid does damage modern 2k paints. I had a feeling it doesn't, but I'm not sure about it.
And as for the business of lining brake hoses to prevent water ingress (as mentioned in the previously attached article), they seem to have solved one non-problem only to create a very real problem in exchange. Flexible hoses block up all the time these days, in a way that used to be unheard of. I am rebuilding a Corvette here in Florida. I bought it as an abandoned restoration project - stripped it right down to the chassis & now putting it all back together. The brake hoses had all been replaced by the previous owner. When I went to re-fit the rear brake hose I instinctively blew through it without thinking, and found it to be completely blocked. The damn thing's never even been on the road!
That's progress, I guess.
Hugo Miller - rebuilding an imported Series II OTS & converting to RHD

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#45 Re: Brake bleeding problems - silicone fluid

Post by chrisfell » Fri Apr 20, 2018 8:10 am

A mention of engines consuming brake fluid reminds me of a dodge used by friends who were into stock car racing in the 1970s. Back then the go to car for performance was the MG Magnette. Built like an out house (especially after the doors were ‘reinforced’ with concrete), twin carbs for acceleration. Older engines were refreshed by a liquid decoke. Used brake fluid was sprayed into the carbs while the engine was reved hard. Lots of blue smoke, but a crisper engine afterwards. No DOT 5.1 in those days, no DOT of any kind. Brake fluid was just brake fluid. It got tired after two years, it ate paint, and if you spilled it on a hot exhaust you could wave goodbye to your car. And your eyebrows.
Chris '67 S1 2+2

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