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Re: Brake fluid compatibility

To: JordanMWJr@aol.com
Subject: Re: Brake fluid compatibility
From: Bschwartz@encad.com (Barry Schwartz)
Date: Tue, 10 Dec 1996 09:00:19 -0800
Cc: triumphs@autox.team.net

> Claiming full ignorance, I must have been asleep in class the day this
> information was covered, and I will admit to not finding the stern warnings
> you reference in any of the service manuals I have on the Triumph (Haynes,
> Standard Triumph Service Instruction Manual, Autobook).


> Last night after reading your post, I evacuated the M/C reservoir, and pumped
> about 2 pints of new DOT 4 through out the entire systems, brake and clutch.
> The condition of the fluid I removed looked good, fairly clear, no black
> grunge I have read on some of the threads lately.


M. W. Jordan, Jr,
Sorry if I alarmed you, the manuals only say to use only DOT4,  No stern
warnings against anything else, but there is a reason, and not just because
girling makes DOT4 brake fluid.  They also make DOT3, and if it was
acceptable the manufacturers would allow it's use.  I can't tell you how
many people used DOT3 in their AMC's that used girling clutch cylinders and
destroyed their seals.  It's hard to say how long it takes.  When we were
running compatibility test on various compounds for our own purposes, some
fluids swelled the seals in a matter of hours, others took several days or
even weeks.  Chances are, the contact didn't harm what you have as long as
you didn't use the system (or even if used but very little).  If used in a
static seal the fluid may be compatible.  Some fluid/seal combinations are
OK for static applications but unacceptable for dynamic (sliding).  Flushing
the system and replacing with the correct fluid will probably restore the
seals to their original design specification.  Just check around the usual
leakage points in a few weeks to see if any fluid is leaking past the seals.
If not, then I wouldnt worry.
    About the black gunk, my master cylinders have had this gunk in them for
as long as I've had the car,  I usually change the fluid about every one two
years (because of various rebuilds/mod's not brake related) and the gunk
returns within a few weeks.  In fact if you carefully examine the master
cylinder reservoirs ( not the early ones using a can type ) there is a
cavity that is lower than the fluid entrance hole.  This is to allow the
'gunk' to collect but not be drawn into the acting part of the cylinder.
Even the brake master cylinders with dual plastic reservoirs have the hole
elevated above the rest of the cavity.  I've only had to rebuild the brake
master cylinder once in the 20 some years I've had the car, and I've never
even touched the front calipers (allthough it would probably be a good idea
- but if it aint broke-).

Barry Schwartz
Bschwartz@encad.com (work)
Bschwart@pacbell.net (home)
(San Diego)
70' Spitfire (under-going major surgery) ,  72'-V6 Spitfire (daily driver)
70'GT6+    


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