Date: 20 Mar 1998 18:10:34 GMT From: "Porcupine" <porcupinenopsametmail.com> Subject: Some Answers
Joe I have investigated this issue, first I have to start with a confession apparently we don't sell silicone brake fluid. The reason being that it isn't accepted by any of the OEM's. Mainly because it suffers greatly from compressibilty and poor lubricity. The poor compressibilty could be overcome by OEM's redesigning the master cylinders and lubricity could be dealt with by the manufacturers of the basefluid (such as Dow Corning). Overall Silicone fluid has a lot of potential due to its boiling point of 260 ?C but isn't easily applied to current systems. One day it may become the defacto but unlikely in the near future. Seal Compatibility If the fluid claims to meet FMVSS 116 DOT 5, then SBR compatibility is required also SAE J1705 requires SBR, EPDM, Natural and polychloroprene compatibility. Backwards Compatibility Silicon fluid must be functionally compatible with SAE J1703 (conventional fluid) and systems designed for such fluid. Functionally compatible means that the brake system will perform with both types of fluid, and that the two can be mixed with no undesirable effects. Of course this doesn't mean "go head mix them", the two fluids are NOT miscible. This means that if you want to go back to glycol then it is possible, but as I mentioned ealier it isn't necessarily a good idea. Silicone is not a pleasant substance to work with and can require some serious flushing as it tends to coat everything it comes into contact with. Water Ingress & Lifespan Water ingress is a possibility through master cylinder vents etc, but the process will be slow and the volume will be minor. Water contamination is a possible problem as water will not mix with the silicone based fluid. Difficulties may arise if water accumulates in pockets (most critically in callipers). The water will boil at 100?C and freeze at 0?C causing system problems. It is worth remembering that Silicone fluids are hydrophobic and as such will not absorb moisture through hoses. Conventional fluid (DOT 3,4, 5.1) is hygroscopic and will draw moisture through hoses. If water contamination is avoided the Silicone fluid will last considerably longer than conventional fluid. I do not have any info on electrical contacts, altitude or combustion byproducts. We do have a lot of info on it but its burried very deep in the records, basically because we have no need to change our current product range. The conclusion is simply this, we are already producing plenty of high temperature fluids without the added complications attached to Silicone. So go get yourself some SRF. Alex
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