More on Silicone Brake Fluid

[Mike Wattam <MikeWattam@domain.elided>]

Hi Nick

Thanks very much for your comments regarding Silicone brake fluid.

If it is any help, I have had Silicone Fluid in my Stag for 12 years now,
used hard (including brakes) every year and no problem.  When I first put
it in, I used the recommendation of the supplier and changed all seals so I
had a completely fresh start.  I understand this procedure is not
mandatory, but it may well explain why some people have problems with
Silicone fluid, it is very likely ester-based brake fluid is still lurking
in their slave cylinders.

I think your problem with the master cylinder may be that you are using a
'reconditioned' master cylinder.  It is customary with these, to hone out
the bores to remove scoring, rust and ridges.  However this is usually done
with a highly inaccurate honing head of the D-I-Y variety, with the result
that the bore may have an abrasive finish, be several thou' oversize thus
reducing seal lip pressure drastically, 'barrelling' or 'bell-mouthing'
occurs and this causes the seals to rapidly fail.  It is usually the rear
seal (nearest servo) which fails and this simply leaks into the servo or
out over the brake pedal area.  Silicone fluid acts as a first-class
lubricant, so it may be that the seals are sliding along the undulations
and allowing fluid through, rather than being forced against the cylinder
wall as they should.

I used Silicone fluid in a Dolomite Sprint for many years, again without
any problem whatsoever, although this car had single-circuit brakes.  I
understand the car is still in use.

I also have it in my Rover Vitesse Sport which gets used very hard in
Europe - up to 150mph for the past 3 years, an MG Maestro 2 litre using
Silicone fluid for 10 years and 140,000 miles.  The other MG Maestro in our
family I have never bothered with and so far this has had 3 sets of rear
brake cylinders in 62,000 miles and the dashbord lights are already
indicating further problems - I didn't bother with Silicone fluid in this
one because it was bought to fulfill a short term need and I really wanted
to be rid of it.

Mike Wattam
Chairman - Triumph Stag Register