Silicone DOT 5 fluie was Re: [alfa] Clutch Master Cylinder Rebuild Questions- 69 Spider

[Bernie Bennett <bennetts77833@xxxxxxxxxxxxx>]

All:

'hygroscopic' AFAI Remember from a DOT 5 silicone brake fluid sales 
pitch I once attended one of its properties was it was not hygroscopic 
as all other DOT versions of brake fluid were.

The pitch went on further to state that 'ordinary' brake fluids were 
agressive absorbers of water, even through the brake hoses. This water 
lowered the boiling point of the fluid causing poor braking performance 
at high temperatures. The advantage of  DOT 5 silicone was it would not 
absorb the water and if put in a totally clean system (new hoses too 
that had no water absorbtion) and in systems scrupulously cleaned of 
other grades of brake fluid,  would keep the systems in which it was 
installed water free.

Further, the sales pitch said, that the US Govt. used it DOT 5 silicone 
in their vehicles esp. for low temp applications where any moisture in 
brake fluid would freeze. Dot 5 silicone kept the system operating.

What I remember/know.

Bernie Bennett
Brenham, TX

> I believe even a closed system like brakes has to have a breather to 
> the atmosphere. Every time you apply and release the brakes a tiny 
> amount of air needs to enter and leave the MC reservoir. To add to 
> that, brake pad wear must be allowed for by air entering the MC 
> reservoir. Humidity in the air is drawn into the brake fluid. I change 
> the brake fluid in my cars at least every four years and often every 
> two years, even though I live in a dry climate. Never had any 
> corrosion in the brake system, anywhere.
>
> Michael Smith
> White 1991 164L
> Original owner
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Keith Walker wrote:

>>>It appears that you are geting severe corrosion in the clutch master
>>>      
>>>
>cylinder that is destroying the internal seals. Do you live near the
>ocean? What are you using for fluid in the MC? If corrosion is indeed
>the problem, I would suggest switching to DOT 5 silicone fluid and end
>this corrosion once and for all. I always change to silicone fluid
>whenever I do brake work on any of my vehicles.<<
>
>As I understand it one of the problems with DOT 5 fluid is that it
>does NOT absorb water and so is prone to allowing water
>to collect in corners of the hydraulic system which causes
>corrosion. Furthermore as the water isn't absorbed it makes
>it more difficult to bleed the system to remove the water.
>
>All the best
>
>Keith
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