Typical brake fluids (DOT 3 and 4) are polyalkylene glycol ether, and
absorb water (up to about 3% max). That's why many systems have a
bellows-type seal so that no opening to the atmosphere is required.
Still, water will creep into the stuff eventually, past seals, etc. (In
humid climates, I understand that brake fluid can absorb its maximum
water content in as little as several months--keep your fluid fresh!)
These fluids also attack most auto finishes (dunno for sure which might
be resistant). "Wet" boiling points for DOT 3 and 4 are 284F and 311F
respectively, with "dry" boiling for these at 401F and 446F.
DOT 5 fluids contain silicone or silicium-based polymers, and have wet
and dry boiling points of 356F and 500F. These fluids are not
hygroscopic, so don't absorb water like standard brake fluids do. They
also don't attack paint finishes. However, they have not been preferred
in racing applications because of air-entrainment problems. They are a
good solution for show cars that aren't driven much.
I'm not familiar with the DOT 5.1 fluids, but my sense is that they are
chemically similar to standard brake fluids and have wet and dry boiling
points of 375F and 518F, and I believe these are often used in racing
applications. Anyone with more info, feel free to tune me up on these
or correct any errors. Thanks.
Benn
----- Original Message -----
From: "Doug Odom" <dlodom@charter.net>
Cc: "landspeed@autox.team.net" <land-speed@autox.team.net>
Sent: Thursday, September 07, 2006 9:10 AM
Subject: Re: ATF or Brake fluid?
> Ed, That is kind of what I'm asking. Is synthetic brake fluid really
> hydraulic fluid? Like I said, I had never even heard of this till the
> other night at the club meeting talking to Tim. Doug Odom in big
ditch
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