Dave,
You mentioned that you checked your DOT5 fluid and found it clear, with
no water. I too installed DOT5 in my TD in 1974 and thought it was
forever and ever without maintenance. As you have done, I have checked
the fluid from time to time, and thought that that was confirming the
mainteance-free nature of DOT5 until I learned that that test may not be
sufficient.
Recently I replaced a rear wheel cylinder that had been sleeved by
WhitePost at the time of DOT5 installation. It was pitted, from water I
suppose, and there were droplets of water in the fluid I drained from
this, and then all the other cylinders.
What I have learned is that, although DOT5 silicone does not absorb
water from the atmosphere, condensation can form in the system and become
little water droplets. These settle out at low points in the system.
I still like the DOT5, but now I believe that it's not the forever
maintenance-free product that it was said to be when introduced. I
believe that bleeding off some fluid every year or two will remove the
water droplets that are likely to occur in our systems that lack a
diaphram in the MC to separate atmosphere from the surface of the brake
fluid.
Bob
On Tue, 26 Nov 2002 15:07:43 -0800 Dave & Liz DuBois
<ddubois@sinclair.net> writes:
> If the switch to silicone is made in a system that has had DOT 3 or
> DOT 4, it must be flushed completely and all the seals replaced. It
> seems that, while silicone and DOT 3 & 4 are not incompatible, if one
is
> put in a system in which the other type has resided and been absorbed
by
> the seals, there is a problem of desorbtion of the one and absorbtion
of
> the other, leading to the seals swelling. If the system is well
flushed
> and new seals installed, there is no problem. I have been using
> silicone in my TD for the past 20 years and have never changed it at
all during
> that time. Not only have I had no problems, but when I checked the
fluid >
> recently, it was still as crystal clear as the day I put it in.
> With no moisture absorbtion, there is no corrosion in the system.
>
> Good luck,
> Dave
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