bodger
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| posted on 14/3/07 at 01:58 PM |
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Silicon brake fluid
Why is it that AP racing don't recommend silicon fluid for their brake components. Wilwood's fluid is also hygroscopic. There is obviously
some issue with silicon as far as these manufacturers go. Any ideas?
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iank
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| posted on 14/3/07 at 02:11 PM |
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Silicone  fluid has some disadvantages, the biggest being a slightly spongier pedal.
http://www.superchevy.com/technical/chassis/brakes/0509sc_fluid/
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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JAG
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| posted on 14/3/07 at 02:44 PM |
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The other issue is with water ingress.
Rather than absorbing the water (like ordinary brake fluid does) the water forms into bubbles within the brake fluid.
Fine until the brakes get hot; then the brake fluid is fine but the water turns into steam and you lose all your brakes 
This all happens at about 100 Celsius (boiling point of water).
With ordinary brake fluids the absorbed water acts to lower the boiling point of the brake fluid - but it usually remains above 200 Celsius (although
it does depend upon the quantity of water absorbed).
So with ordinary brake fluids total brake loss doesn't occur until much higher fluid temperatures have been reached.
Justin
Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!
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Mr Clive
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| posted on 14/3/07 at 02:58 PM |
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As already mentioned, silicone fluid will not absorb water like normal hydraulic fluid. Consequently "bubbles" of water form which not
only boil easily but also compress more than the fluid leading to a spongey pedal.
Also these water pockets are far more corrosive to metal brake componants than normal hydraulic fluid contaminated with the same amount of water. Not
really a hugh problem for race cars which will be rebuilt often but a valid concern for road cars.
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speedyxjs
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| posted on 14/3/07 at 03:59 PM |
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Silicon? Just dont let it get anywhere near your petrol tank. 
How long can i resist the temptation to drop a V8 in?
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02GF74
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| posted on 14/3/07 at 04:24 PM |
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funnily enough was reading bout silicon fluid the other day, can't recall whre though.
downshot was don't use it for reasons stated above; water sinks to lowest part of braking system making it dangerous should the brake temps
exceed the boiling point (plus allow some for the pressure).
dot4/5 is plenty good enough unless you are F1.
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Ivan
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| posted on 14/3/07 at 04:31 PM |
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Used it for a few years on my cobra - the rubber flexible hoses eventually swelled shut switching off the front brakes  Never again.
Also told it absorbs air instead of water which also boils off giving low pedal.
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MikeRJ
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| posted on 14/3/07 at 04:51 PM |
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quote:
Originally posted by Ivan
Also told it absorbs air instead of water which also boils off giving low pedal.
It tends to keep minute bubbles of air trapped much more than mineral fluid does, which gives the spongy pedal. It's disadvantages greatly
outweigh any advantages IMO.
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RazMan
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| posted on 14/3/07 at 06:00 PM |
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I think I read somewhere that you should only use silicone (if you really really must use it at all) when you assemble a new system - you can't
change the fluid from conventional fluid as all the parts will be contaminated. Thats probably why Ivan had problems.
I wouldn't use it as modern fluids are perfectly adequate for normal use - Dot 5.1 is the best imo.
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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britishtrident
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| posted on 14/3/07 at 06:36 PM |
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Best to stick with conventional fluids, also avoid racing fluids unless you want to change the fluid every 3 to 6 months.
The higher the boiling point of a conventional fluid the more hydroscopic it is, for this reason after 6 months a racing fluid will have a lower
boiling point than DOT 4. The same applies to a lesser extend to DOT5.1 fluids after 18 months in a damp climate the boiling point will be lower than
a DOT 4 fluid of the same age.
Silicone fluid has its place on vehicles that are stored for very long periods.
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designer
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| posted on 14/3/07 at 07:30 PM |
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All brake fluid is hygroscopic. That's why you should only buy the small tins and never leave it open.
Silicon brake fluid is compressable.
Don't use it!
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iank
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| posted on 14/3/07 at 08:21 PM |
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quote:
Originally posted by RazMan
I think I read somewhere that you should only use silicone (if you really really must use it at all) when you assemble a new system - you can't
change the fluid from conventional fluid as all the parts will be contaminated.
...
Yes they are incompatible. If you change to silicone you need to change all the rubber seals in the system else they swell up. Not sure how
you'd flush the pipes without using loads of new fluid.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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