Silicone Brake Fluid

[Mike Wattam <MikeWattam@domain.elided>]

I wish I had never got involved in this!

I have talked direct to Lockheed and they categorically state that Silicone
brake fluid must almost never be used in automotive braking systems.  They
say it gives a spongy pedal, the brakes can lock 'on', and the fluid boils
at a very low temperature.  They say it can only be used for storage
purposes as it does not corrode brake components.  They also said
ester-based fluid does not absorb water and boil to result in the loss of
brakes.  They also do not make or distribute Silicone fluid.  They were
completely at a loss to explain why my own Stag has performed completely
reliably with silicone fluid for over 10 years.  They also said all brake
fluids should be changed completely every 18 months or less.

So I have also talked direct to Girling, their major UK competitor. 
Girling say 'swings and roundabouts'.  The only reason they would say
ester-based fluid has a technical 'edge' is in lubrication of the seals -
they can wear more quickly if Silicone fluid is used.  They say the boiling
point of silicone is much higher, it is non-corrosive and there is no
noticeably greater compressability of the fluid.  Thus it is a high
performance fluid and the only reason they say it is not widely used, is
that it is expensive.  They say either fluid should be changed every 2
years.  They sell Silicone-based fluid as their DOT 5 fluid although they
do not refer to it on the packaging as Silicone fluid.

These views by major UK brake manufacturers are in direct conflict.  

So, in desperation I spoke to Williams Racing as they not only run Formula
1 cars, but also run Renault Laguna saloons in some very fast saloon car
racing.  Surprise, surprise.  They only use Silicone fluid due to its high
temperature capabilities, and find no greater compressability.  They also
said they never use the fluid for very long because the drivers tend to
knock the wheels off regularly !!!  On F1 cars the brakes are often rebuilt
between races.  I guess they gotta get better drivers!

Now, it is up to you to make your own decision.  The only common factor
that comes out is to change the fluid regularly, bad news as this is a
horrid job.  So if we follow this advice, on cost grounds alone the
ester-based fluid will win, but the Silicone will win if you want fade
resistance, expect to get water in your braking system and don't want
corrosion problems.

As I said, next time I'll keep my mouth shut.

Mike Wattam
Triumph Stag Register