Re: DOT 5

[Luis Marques <marques@raytheon.com>]

"Greg Herrmann" <airtech@isoc.net> wrote:
>
> I am considering changing over to DOT 5 brake fluid.  What do I need
> to do for the conversion?
> 
> Greg Herrmann
> 84 CGT
> 86 CGT
> 93 NSX


In a word, "don't".  DOT5 is not compatible with DOT4 and you will have
to completely flush all the system (if not completely rebuild it). 
These are mostly silicone-based fluids that don't absorb water, and are
intended for museum cars that don't get driven but maybe once a year. 
The fluid itself is more compressible than DOT4 (spongy pedal), and
since it doesn't absorb moisture, the little moisture that makes its way
into the system stays undiluted causing much more rapid and severe
localized corrosion.  Plus there have been tales of brakes staying
locked up like if you have the parking brake on...  in the middle of the
road after a light turns from red to green... not fun.

IMHO, there are lots of great DOT4 fluids out there that are much better
suited for high performance driving like ATE Super Blue ($10/qt.), or
the super high temp. Castrol SRF (sp?) (at $70/qt.), or even the Castrol
LMA ($5/qt.) For a track car (and if you have tons of money) it will be
very hard to find anything better that the Castrol SRF stuff (as used by
the indy cars an the like).  For the rest of us without six digit bank
accounts, ATE Super Blue (or the Type 2000 amber variant) is probably
more than adequate with high dry and wet boiling points and they have
low moisture absorption.  This is stuff you can put on your car and just
flush once every year or two.  The Castrol LMA still has decent wet and
dry boiling points with low moisture adsorption and it too can be
flushed every year or two.

Then there are other fluids out there that have very good dry boiling
points, but absorb moisture faster and their wet boiling points aren't
that great (like Motul and others).  These are fine if you track your
car a lot and flush it before every event.  One of these fluids that is
often overlooked is the "super heavy duty" DOT 3 or 4 fluid that are
sometimes spec'd for trucks.  They are very cheap, but you will have to
flush more often as they degrade faster and have relatively low wet
boiling points.  HTH

Luis Marques
'87 4kcsq