Re: Silicone Brake Fluid

[Michael Burdick <mburdick@domain.elided>]

On Tue, 1 Sep 1998, Glenn Merrell wrote:

> I would think that in application, a Stag in normal road conditions
> would still benefit from a higher temp based fluid, and, if a fluiod
> does not attract fluid readily, possibly would help maintain the system
> if the cap is left in place.

Hi Glenn and everyone,

Four or five years ago, I wrote the following bit to the british-cars
email group.  FWIW, I use DOT5 (silicone) in my daily driver Spitfire (for
7 years now), and DOT4 in the Stag.  If/when the Stag needs a brake
rebuild, I will probably go to DOT5 in that too.  Incidentally, DOT5 means
silicone and vice versa.  DOT 5.1 is NOT silicone however, nor is silicone
DOT 5.1 - clear as muddy water, right?!

Take care,
Mike Burdick
Omaha NE
'72 Stag

----- 
A while back when this topic came up, I posted excerpts from a
Skinned Knuckles article on silicone brake fluid.  They made the best
attempt I've seen so far to actually address this issue with hard data
instead of anecdotes.  The data they used came from military tests in
jungle conditions and tests from the original producer of DOT5 fluid
(DuPont? I can't remember...).  Even so, they were not able to come up
with many conclusions about DOT5 fluid. In a nutshell, the conclusions
were:

1. DOT5 does not absorb (i.e. mix with) water and may be useful where
   water absorption is a problem.

2. DOT5 does NOT mix with DOT3 or DOT4. They also maintain that all
   reported problems with DOT5 are probably due to some degree of mixing
   with other fluid types. They said the proper way to convert to DOT5 is to
   totally rebuild the hydraulic system.

3. Reports of DOT5 causing premature failure of rubber brake parts were
   more common with early DOT5 formulations.  This is thought to be due to
   improper addition of swelling agents and has been fixed in recent
   formulations.

4. DOT5 is compatible with all rubber formulations.

5. DOT5 doesn't eat paint.

They also made some general recommendations based on this data and
personal experiences. These, along with recommendataions of list members
included:

1. If it works for you, use it. You won't hurt anything if you do the
   conversion correctly. (See, #2 above)

2. Careful bleeding is required to get all of the air out of the system.
   Small bubbles can form in the fluid that will form large bubbles over
   time. It may be necessary to do a series of bleeds.

3. DOT5 is probably not the thing to use in your race car although it is
   rated to stand up to the heat generated during racing conditions. The
   reason for this recommendation is the difficult bleeding mentioned above.

4. DOT5 is a good choice for the weekend driver/show car. It doesn't
   absorb water and it doesn't eat paint. One caveat is that because it
   doesn't absorb water, water that gets in the system will tend to
   collect at low points. In this scenario, it would actually be promoting
   corrosion!  Annual flushing might be a good idea.