FWIW.. from the "Big" Healey list....... Hope it helps
Peter C
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A comment by Brian Smart, Service Technical, AP Lockheed
We are often asked by members of classic car clubs similar to the TR
Register, what are the benefits of Silicone brake fluid?
AP Lockheed neither markets such fluids nor recommends use with our own
or any other braking system, unless specifically designed to use such fluid.
Virtually all problems relate to :
-Long/spongy pedal
-Sudden loss of brakes
-Hanging of brakes
They reflect certain properties of silocone fluids (advocated) by us over
many years and recently ratified in SAE publications, namely:
-high ambient viscosity
-high air absorption
-high compressibility
-low lubricity
-immiscibility with water
Research has shown that the relationships between problemes reported and
properties identified may be expressed as follows:-
Long/sponge pedal
a) Compressibility up to three times that of
glycol based fluids
b)High viscosity, twice that of Glycol based fluids, leading to slow rates
of and retention of free air entrapped during filling and hence bleeding
difficulties.
Sudden loss of brakes
a) air absorption. Gasification of absorbed air at relatively low
temperature produces vapour lock effect.
b) Immiscibility (failure to mix) with water. Whilst the presence of
dissolved water will reduce the boiling point of glycol based
fluids any free water entrapped in silicone filled systems will boil and
produce vapour lock at much lower temperatures (100*C or thereabouts).
Hanging on of brakes
a) Low lubricity. In disc brake system [in] the sole mechanism for
normalization of system pressure upon release of pedal
pressure is a designed -in tendency of (the) seals to recover to their "at
rest" attitude. Low lubricity works against this tendency.
b) High viscosity, exacerbating the effect of a) above
It should not be assumed, therefore, that the high price of silicone
fluids implies higher performance in hard driving or even normal road use.
AP Lockheed glycol based fluids do not contain the adverse properties
described above. The recently introduced
SupremeDOT5.1 which exceeds the performance criteria of DOT 5 is siutable
for all conditions likely to be encountered in modern driving conditions.
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