Doug,
Steve handled the electrolysis myth, but let me comment a little about my
experience with brake fluids, primarily silicone and Castrol DOT 4. I
think the property of brake fluids to absorb moisture should be viewed as a
virtue, not a drawback. Ideally, brake fluid should take up moisture and
prevent it from both corroding the brake system and lowering the boiling
point. No brake fluid is perfect, but this is the idea. Water, however is
immiscible in silicone oil, so any water that gets into your system just
collects in nooks and crannies and does its mischief, as you discovered
when you opened the reservoir. Many years ago I jumped on the silicone
brake fluid bandwagon because it seemed like such a good idea; doesn't ruin
your paint, has a high boiling point, and is pretty inert. Pretty soon
everyone that was doing any racing found out that silicone was a very bad
idea because of brake fade due (I presume) to boiling of moisture in the
system. If you only drive around town and especially if you are afraid of
getting it on your paint, by all means use it. But I would recommend
flushing the system periodically to remove moisture.
I've always wondered how moisture gets into a closed hydraulic system. The
most likely way is through the vent hole in the reservoir cap, so be
careful when washing the car, etc. You can get rubber moisture barriers
that fit in the reservoirs from Tiger Technologies which should help (all
modern cars have them). Maybe some moisture works its way past the slave
cylinder seals, etc., but you would think that if this can happen, then
brake fluid could leak the other way. Maybe just a little moisture adheres
to the cylinder walls and gets transferred that way. In any case, by hook
or by crook, you can count on moisture eventually getting into the
hydraulic system, so it is important that the hydraulic fluid scavenge the
moisture and minimize its effects. Even if you don't do any serious
racing, etc. its probably worth the approx. one hour it takes to once a
year completely flush the hydraulic systems in your car.
I seem to have a lot of trouble with my clutch hydraulics. I've replace
the slave cylinder every couple of years or so. Partly to blame is the
heavy duty clutch I'm running; probably stronger than needed. Next time
around I want to put in a Centerforce which is real easy to operate and is
very similar to stock 5.0 Mustang clutches. Another source of problem is
the heat it gets in proximity to the headers. A little shielding might
help this problem. What I'd really like to do is sleeve a slave cylinder
in stainless. A friend of mine swears by silicone fluid in this
application; says his problems went away when he switched. I'm giving it a
try, but am a little skeptical. Getting an empty system primed with
silicone seems a problem (too viscous?), so it's easier to start with
Girling/Castrol and then bleed through the silicone fluid.
My recommendation for the brake system is to stay away from silicone unless
you have a show car paint job and are paranoid about getting fluid on it.
It's your call about using silicone in the clutch system, just don't wait
another seven years before flushing it whichever you use.
I've gone way past my allotted bandwidth, so I'll sign off now.
At 09:35 PM 10/20/97 -0600, you wrote:
>When I last rebuilt my clutch hydraulics, I used NAPA DOT 5 silicone brake
>fluid to refill, all components being clean, dry and empty. granted that
>was about six or seven years ago, but when my clutch system developed a leak
>this week, and I refilled and bled it, I was surprised to find a layer of
>murky water at the bottom of the bleed jar. I thought silicone was not
>hygroscopic (moisture absorbing). Anyone have similar experiences?
>
> Also the reason I didn't use silicone in the brakes at that time was the
>rumor that the brake light switch in the tiger which allowed current to pass
>through the brake fluid, caused polymerization of the silicone, resulting in
>a gum forming inside the lines at that point. Is this a myth or fact?
>Never been able to confirm or deny it.
>
>Doug Huggins
>Colorado Springs
>
>
>
Bob Palmer
UCSD, AMES Dept.
rpalmer@ames.ucsd.edu
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