Re: Brake fluid FAQ development

["Christian Els" <tiAn@usiw.net>]

Not sure who the keeper/editor/assembler of all this is, but I'll add some
comments, below:

----- Original Message -----
From: "Brian McGarvey" <brianm@zbt62.eastnet.gatech.edu>
Cc: <scirocco-l@scirocco.org>
Sent: Monday, 12 March, 2001 07:29
Subject: Brake fluid FAQ development


> With all the bouncing around about brake fluid
> how about the experts make a FAQ adn put it up on the tech tips...
> My donation: I deleted all the old messages but hey.. we can start here
> and fix it.
>
> DOT 5 -- main advantage paint safe but requires different seals (Harley
> has been using it for years on thier leaky motorcycles)
> insert avg boiling temp here
>

DOT 5 is silicone-based and is not hygroscopic, meaning that it does not
absorb water from the atmosphere. It has a high boiling point (in the
neighborhood of 550 degrees, depending on whose you get), but has a
questionable impact on the performance life of seals in a system which does
not suffer questionable things well.

The other standards, DOT3, DOT 4 and DOT 5.1 are all alcohol-based compounds
and ARE hygroscopic which means any of them, from the CheapAss DOT3 special
to Ate Super Blue to Motul 600 all suck water out of the sky. This is the
reason for periodic flushing of brake systems - the added water results in
mushy brakes and increased fade at high temperatures.

There is some concern with DOT 5 use that because the water is not absorbed
into the fluid, it must remain on the surfaces of components within the
system causing increased corrosion. I will say from my experience this is
not true, based on working on US Army trucks (as a fleet these use DOT 5)
for ten years and using  DOT 5 in my motorcycles (not Harleys) for over 5
years.

Regardless of my experience, I do not suggest you switch to DOT 5 without
fully exploring the potential consequences and making an informed decision.

DOT 5 is very safe for painted surfaces and plastics.


> DOT 4 -- main advantage higher boiling point than DOT 3 std motorcycle
> brake fluid.. (does/ does not require seal changes???)
> insert avg boiling temp here
>

DOT 4 has a minimum spec boiling temperature of 400 degrees F. Better
quality fluid improves that point up north of 600 degrees.

> DOT 3 -- standard fluid cheap, stock in most cars.
> insert avg boiling pt here
>

DOT 3 is an ancient standard that is easily met by lost substance which are
liquid at normal atmospheric conditions. I don't recall the specifics of the
standard.


> Ford Heavy Duty -- used as Cheapass Ron(tm) racing solution very high
> boiling point doens requrie frequenct changes as doesnt absorb water.
>

This is a DOT 4 fluid.. It absorbs water at roughly the same rate as any
other DOT 3/4/ 5.1 fluid, but has a higher boiling point making it better
suited for applications requiring sustained hard use of brakes - racing,
towing, mountainous travel, etc.


> Blue ATE -- very high temp fluid has to be changed regularly (interval)
> for sustained braking power as it absorbs water
>

The Ate Gold has the same properties as the Blue, but is color coordinated
so you can tell when to stop flushing the old fluid (Ate suggests that you
alternate between Gold and Blue so you know how much fluid to expunge each
time by waiting for the color change at the bleeder nipple).

 Regards,

Christian
87 16V



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