The following is a post that Roger Parker made to the MG BBS
back in early August ... the OEM's warning/recommendation
certainly merits consideration.
Safety Fast! ... larry.g.unger@lmco.com
'61 MGA 1600 MkII
> Subject to comments before but a recent problem on this BBS and
> a couple of others outside to me recently have brought it back
> into the fore. I have the current Lockheed brake parts books
> and there is a page of information specifically on Silicone
> brake fluids. I reproduce it below for those who do not have
> access and anyone else with interest...
>
> "Silicone Brake Fluids - Beware
>
> Our technical service department is receiving an alarming number
> of calls from motorists reporting problems with silicone fluids.
>
> AP LOCKHEED NEITHER MARKETS SUCH FLUIDS NOR RECOMENDS THEIR USE
> WITH OUR OWN OR ANY OTHER BRAKING SYSTEM.
>
> Virtually all the problems relate to:-
>
> long and spongy pedal
> sudden loss of brakes
> hanging on of brakes
>
> They reflect certain properties of silicone fluids identified
> 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 problems
> reported and the properties identified amy be expressed as
> follows:-
>
> Long/spongy 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 fill 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, Imiscibility (failure to mix) with water. Whilst the
> pressence 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 degrees Celcius or thereabouts)
>
> Hanging on of brakes
> a, low lubricity. In disc brake systems the sole mechanism for
> normalisation if system pressure upon release of the pedal
> pressure is a designed in tendency to recover their 'at
> rest' attitude. Low lubricity works against this tendancy.
> b, High viscosity, exacerbating the effect of (a) above.
>
> It should not be assumed, therefore, that the high price of
> silicon 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 Supreme DOT
> 5.1, which exceeds the performance criteria of DOT 5, is
> suitable for all conditions likely to be encountered in modern
> driving conditions."
>
> That is straight form AP. I have experienced soem of the
> problems described above with cars using silicone fluid and I
> have seen these problems dissapear when the system has been re-
> sealed and re-filled with glycol based DOT 4 fluid.
>
> There will be those who will claim many advantages but my
> experience and contact with so many owners reporting similar
> problems sets a trend that 'points the finger'. When it comes
> to brakes it's not worth taking any chances.
>
> For those wishing to argue the above please direct your
> comments direct to AP Lockheed, PO Box 12, Tachbrook Road,
> Leamington Spa, Warwickshire, England. CV31 3RL.
|