<VV> brake help

[Hugo Miller]

I decided to see if I could find the basis for some of the claims 
against silicone brake fluid. This site had an interesting article, 
including some pics of what happens when you mix silicone & non-silicone 
fluid; The (purple) silicone fluid sits on top of the DoT4. But shake it 
up & let it settle & the colors are reversed! This is allegedly due to 
the DoT4 absorbing the purple dye from the silicone fluid.

http://www.buckeyetriumphs.org/technical/Brakes/Fluid/Fluid.htm

This site also mentions compressibility in some detail. It blithely 
states that silicone fluid is more compressible than DoT4, ignoring the 
well-known fact that liquids are not supposed to be compressible! (nor 
is rubber, of course).

    "Compressibility: The one real problem found with the silicone fluid 
is that it is more compressible than glycol fluid, especially at 
elevated temperature.  G W Holbrook of Dow Corning Corporation reported 
on Alpine testing of Silicone Brake fluids at a SAE meeting in 1981 
(another report Hugh Fader gave me).  Alpine descents are used in Europe 
to study brakes.  Similar tests are run in the US.  The long hills 
provide a good test bed to apply brakes repeatedly to get the 
temperature high enough to make the brakes fail."

The short answer is that yes, silicone fluids do give a softer pedal, 
but not really enough to notice.

Another thing I learned is that rubber brake hoses can not only absorb 
moisture, but also salt, which is a rather scary thought. That probably 
accounts for another recent phenomenon, of hoses becoming blocked or 
acting as one-way valves, because they now have a membrane to prevent 
moisture ingress which, in typical fashion, seems to cause more problems 
than it cures.

My (British) Morris Minor brake system is pressurized to 2 or 3 psi, 
which keeps the seal lips expanded and stops all the nasty stuff getting 
in through the hoses.



On 2019-01-23 21:25, Frank DuVal via VirtualVairs wrote:
> I can tell you from almost 40 years of DOT 5 use that this internet
> warning is a bunch of hokum, like most unsubstantiated things one
> reads on the Internet, HA!
>
> I give real world experience I have with the product.
>
> Not being hygroscopic is the benefit of DOT 5, not a problem to be
> reckoned with. If it was, I would have line failure from the inside 
> on
> my cars sometime during the last almost 40 years. Always rust from 
> the
> outside in is the cause.
>
> I will say I never used DOT 5 in a system using DOT 3 without
> rebuilding the system. Why would I? I’m trying to make a brake system
> that lasts for years, not pour expensive fluid in with who knows 
> what,
> including all that d#$& white corrosion that DOT 3 brake systems have
> after a few years.
>
> Frank DuVal
>
>> On Jan 23, 2019, at 7:15 PM, Hugo Miller via VirtualVairs 
>> <virtualvairs at corvair.org> wrote:
>>
>> I presume the significance of your living near the ocean is that 
>> there is more moisture in the air? I have heard that since silicone 
>> fluid isn't hygroscopic, any moisture in the system will 'pool' at the 
>> lowest points & just sit there causing corrosion, rather than mixing 
>> with the fluid (where it can be flushed out every time you change 
>> brake fluid).
>> I have no idea whether that is correct, but to me it is just another 
>> reason to be wary of silicone fluid, since its major advantage might 
>> in fact be a disadvantage.
>>
>>
>>
>>> On 2019-01-23 16:10, Steve Gangi via VirtualVairs wrote:
>>> I'd like to add my two cents as a rubber chemist.  1. When a new
>>> rubber seal is exposed to a fluid for the first time it becomes
>>> conditioned to that fluid (swells) and takes a set. When that fluid 
>>> is
>>> removed, the rubber slowly recovers (shrinks). DOT 3 brake fluid 
>>> and
>>> Silicone are very different. They do not mix and cause different
>>> swelling. Once a brake part has been swelled once in DOT 3 it will 
>>> not
>>> re-swell to the same dimensions in silicone and probably leak. 2. 
>>> If
>>> you are putting silicone into a system previously containing DOT 3 
>>> you
>>> should at least clean the system with alcohol and dry out 
>>> completely
>>> by blowing compressed air through the lines. Then take apart the
>>> cylinders and wipe all the rubber cups off with alcohol. If you are
>>> going to go through all that, you might as well put in new rubber 
>>> cups
>>> or new wheel cylinders. I have had similar experiences as many of 
>>> you;
>>> great results with new parts and mixed results taking short cuts. I
>>> live near the ocean and silicone is a necessity for old cars. Steve
>>> GangiBranford, CT6 Corvairs
>>> ___
>
>  _______________________________________________
> This message was sent by the VirtualVairs mailing list, all
> copyrights are the property
> of the writer, please attribute properly. For help,
> mailto:vv-help at corvair.org
> This list sponsored by the Corvair Society of America,
> http://www.corvair.org/
> Post messages to: VirtualVairs at corvair.org
> Change your options: 
> http://www.vv.corvair.org/mailman/options/virtualvairs
> Archives: http://www.vv.corvair.org/archive.htm
>  _______________________________________________