For some reason, I have recently had a spate of queries about this stuff. So I thought I'd do a quick tech thing on it, seeing as most of the little available information is seemingly misleading.

'Into the valley of death, rode the six hundred.........' No, this isn't about silicone microchips, or anything about computers at all. Having just done that stuff on disc brakes, it prompted me into thinking about the braking systems as a whole, one thing lead to another, and, well, and brake fluid. More exactly, silicone based brake fluid. For some reason, I have recently had a spate of queries about this stuff. So I thought I'd do a quick tech thing on it, seeing as most of the little available information is seemingly misleading. Silicone based brake fluid has been heralded by some as being the last word in brake fluid, yet also brings a look of horror onto the faces of some. Strange, eh? The classic car folk swear by it, particularly for vehicles that are not used much where brake seal failure car be experienced, and because it does not affect paintwork. A number of racers go pale at the thought of using it. So what's the score?

Basically it goes like this...................... A majority of the problems suffered relate to three main areas - long or spongy pedal feel, sudden loss of brakes (ulp!), and brakes 'hanging on'. S A E publications have ratified these symptoms by identifying certain properties prevalent in silicone brake fluids. These have been named as high ambient viscosity, high air absorption, high compressibility, low lubricity, and immiscibility with water (failure to mix with water). It would seem that there are definite relationships between these properties and symptoms, and they go like this: LONG/SPONGY PEDAL - the compressibility of the silicone-based fluid is up to three times that of the more common glycol based types, so needs more pedal travel to actuate. Its viscosity is twice that of the glycol-based fluid - meaning it is thicker. This equates to slow fill rates that can trap air, and results in bleeding difficulties. SUDDEN LOSS OF BRAKES - Entrapped air stays suffers gasification at relatively low temperatures, causing a vapour lock effect. It's immiscibility causes any free water caught in the system to boil at relatively low temperatures - producing a vapour lock. Glycol based fluids absorb water (the water dissolves into the fluid), and although this will reduce the boiling point, it is unlikely to cause severe vapour lock at low temperatures. HANGING ON - In disc brake systems, the sole mechanism for returning the pads to their normal 'not in use' position away from the disc is the tendency of the seals to recover to their at rest attitude once the pedal is released. The low lubricity of the silicone based fluid works against this recovery; it's high viscosity amplifying this effect. So, just because silicone brake fluid costs loads of dosh in comparison to its glycol based counterpart, it does not mean that a higher performance will be achieved. And just to underline this, neither of the major brake specialist companies in England produces silicone based brake fluid. In fact they are most emphatic in their condemnation of it. Think on.

Importation rules regarding vehicles are very specific: Only those over 25 years in age may be brought in to the USA without compilance to Federal Motor Vehicle Safety Standards (FMVSS).