From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: NO BRAKES !!!!
Date: Sun, 14 Sep 2008 21:52:33 -0400
Message-ID: <n4frc45q8vo15lcb44j77mv5gu139fjo6a@4ax.com>

On Sun, 14 Sep 2008 17:12:44 -0500, "Steve Barker DLT"
<railphotonut@always.hotmail.com> wrote:

>Bzzzzzzzzzzzzzzzztttt!  Wrong answer again.  Where do you suppose this
>alledged 'moisture' gets in?  If you never open the mc and don't mess with
>it all the dam time, there will be NO no moisture in the system.
>

Damn, it's embarrassing to be a smart ass AND be wrong...

The source of the moisture is via two routes.  The minor route is diffusion
through the rubber hose.  The more significant source of moisture - in exactly
the worst spot too - is diffusion through the rubber seal on the caliper
pistons.  There is probably also an element of introduction involved when a
very hot caliper is quenched by splashed water but I don't have any supporting
research on that aspect.  I DO have an SAE paper written by a team of OEM
engineers that verifies the above mentioned pathways.  The authors identify
several "enhancing" conditions including brake pads near the end of their
lives which causes the piston seal to rest on dirty and/or rusty cylinder
walls.

This is not a process that happens overnight, over a couple of years or, as I
heard one asshole service advisor tell a woman at a Volvo dealership, every
15,000 miles.  But moisture DOES build up over a half a decade or more.  I
experienced the effect in my Datsun Z when I took it to the track.  At that
point the brake fluid down at the calipers was probably >10 years old.

Sometime in the 90s, the industry adopted a modified brake hose structure that
includes a moisture barrier layer.  Yep, there's an SAE paper on that too.
That leaves only the piston seal route.  Still a potential problem but if one
doesn't wear the pads down to the metal, probably not a serious one.  I know
that my 94 Caprice still has the original fluid and has no brake problems on
track days even though the rotors will frequently billow smoke from
accumulated grease and street driving debris.

John