[Healeys] Silicone DOT5 brakefluid for the 100

Oudesluys coudesluijs at chello.nl
Mon Nov 9 07:40:23 MST 2009


Although DOT5 has its advantages in:

-not stripping paint like DOT3/4 (I do not know if this also true for 
DOT5.1)
-less detoriation being not or less hygroscopic
-higher dry and wet boiling point
-long life

 there are also some negative sides to it:

-little or no water absorpsion
-slightly spongy brake pedal, hence the recommendation to use Teflon 
SS-braided brake hoses.

You will always get some condensation in the brake fluid reservoir and 
the fluid will also absorb water from the air, even right through the 
seals. With DOT5 this is to a far lesser degree and eventually water can 
end up as droplets in the lower regions of the brake system, often in 
the callipers or brake cilinders, causing havoc. Because of the 
durability of DOT5 most people tend not to change the fluid regularly, 
thus the water will not be expelled from the system and this will be the 
cause of corrosion  in the end.
 
DOT3, DOT4 or DOT5.1 is less compressible than DOT5 and will absorb the 
moisture thus preventing corrosion to a certain point but also the 
boiling point will be getting to low. That is the reason it should be 
replaced every 1-3 years, depending on conditions.
You can mix DOT4 and 5.1 with DOT3, but you should never top up DOT4 
with DOT3 or DOT5.1 with DOT4/DOT3.
You cannot mix DOT5 with DOT3/4/5.1.

There is also DOT6 but that is for militairy applications only.

I know of a lot of people preferring DOT5. I prefer DOT 4 or 5.1 because 
of its incompressability and water absoption as I am living in a country 
with often a high humidity. I change the brake fluid in all my cars 
every 2 years.

Kees Oudesluijs
NL

> Since I can only recommend to use DOT5. Its the best I have ever done as
> brakes are concerned. No mess with leaking and paint eating brake fluid
> anymore.
>
> Josef Eckert
> Konigswinter/Germany
>   
Betreff: [Healeys] Silicone DOT5 brakefluid for the 100
> Some years ago there was a discussion whether to use DOT 5 brake fluid in the
> 100 or not. As far as I understand you should make some modifications to the
> brake master cylinder when using DOT 5 fluid. Can anybody tell me precisely
> what these modifications were?.
>
> Thomas Willig


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