Silicone Brake Fluid

[TerryBeck]

Can anyone tell me if there are any disadvantages to using silicone brake fluid? It doesn't absorb water, it doesn't corrode paintwork, I believe it has a higher boiling point than conventional fluid, so why is it (apparently) never used as standard on any new production car that I know of? Obviously, it's more expensive, but is that the only reason?

Terry

[Martec]

Hi Terry,

I used it in my 61 MkII in the clutch and brake system. I had rebuilt the car from a wreck and it had all new seals, pipes and hoses and wanted the best that I could use. After a short while I found the hydraulics worked well, but the brakes would take 5 seconds to release after removing my foot (I timed it).

Ken Jenkins supplied the answer, the servo has lockheed rubber seals and my calipers had Girling seals (girling 3 pot at front and XJ6 at the rear), Lockheed seals don't like silicon fluid, expand and jamb in the servo.

I flushed the system out with DOT4 fluid and all has been fine since, but it is replaced every 2 years to remove the entrained water and stop corrosion.

Silicon does not absorb water but what does get in travels to the lowest point and corrodes there.

Brian

[TerryBeck]

Thanks Brian. I must say, I haven't experienced the problem you've encountered and I've been using silicone fluid for some years. It was just a conversation with a fellow enthusiast (who himself didn't know the answer) which caused me have doubts and to ask the question after I've just done a rebuild.

Terry

[PeteB]

I think the main difference in operating is that silicone doesn't have the same lubricational properties as mineral fluid. This doesn't tend to affect larger working parts like calipers & wheel cylinders, but something like a brake servo might be more prone to sticking.