Thanks to all who jumped in here- since the entire system, including lines,
is being replaced in the restoration, I'll just switch to the silicone fluid
and be done with it.
Jon
'77 (mostly) 1500 "Ol' Yeller"
FM66043 7U
www.bigolbear.com/restoration.htm
-----Original Message-----
From: spitfires-owner@autox.team.net
[mailto:spitfires-owner@autox.team.net]On Behalf Of Terry Thompson
Sent: Monday, March 25, 2002 8:24 PM
To: spitfires@autox.team.net
Subject: RE: { NASS } Brake Master Cylinder
The only thing that is not compatible with british
rubber (which is usually a natural rubber derived from
extracts of rubber plants) is that it brakes down very
quickly when it comes into contact with petroleum
products. This is why you should use girling/castrol
LMA fluid; a mineral based fluid.
U.S. manufactured rubber is usually a petroleum based
item (Contains no natural ingrediants...Just like a
Hostess Twinkie!) and is safe to use with Dot3 brake
fluids. It will eat through paint like LMA/dot 4, but
it's not the same. Dot 3 (what we use in every
american vehicle) will eat british natural rubber so
that the seals will be useless within a year's time.
When I first bought my car, I topped off the brake and
I believe the clutch with Dot3...Big mistake. Since it
was only topped-off, it took about 3 years to
sufficiently do the damage, but when it did go, the
pedal went to the floor. Upon taking everything apart,
the seals looked like they'd been nibbled-on by voles.
The fluid will turn brackish/black from the disolved
rubbers.
The only reasons not to use silicone in your spit are:
-It's expensive (about $10 per quart compared to
$2.50/pint for LMA)
-It's got a squishier feel to the pedal. Some people
that like the pedal very stiff and responsive may
revert back after they've tried it.
-You have to replace or clean every part (master,
wheel cylinders, lines, PDWA, calipers) with denatured
alcohol before filling the system. It doesn't mix with
LMA.
-It's non-hydroscopic. <-it doesn't absorb water. LMA
fluid is VERY hydroscopic. This is good and bad. A
bottle of silicone can sit on your shelf for years and
you can use it to top off your car. LMA should be
opened, used once and then disgarded, as ambiant
humidity will find it's way into the container. Of
course, because silicone is non-hydroscopic, water
that DOES get into your system, will not be absorbed
into the brake fluid and will eventually rust any
metal parts it has settled against; brake lines,
cylinder bores etc.
-Finally, silicone has a higher boiling temperature,
but it's heat dissipation is worse than LMA. That is
to say, when silicone gets hot from repeated braking,
it stays hot and heats up to boiling much quicker than
LMA. For this reason, it's frowned upon by racers.
This not really an issue with a casual driver/cruiser.
-Terry
Yahoo! Movies - coverage of the 74th Academy Awards.
http://movies.yahoo.com/
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