Silicone brake fluide in an '88 Carerra

[saurkraut]

A friend of mine (who will remain nameless) just put silicone brake fluid in his '88 Carerra.

He just bought it, and the calipers were sticky. It had blue brake fluid in it and I told him it was probably ATE Super Blue.

Anyway, I came back a week later and he had 4 new calipers on and bled with silicone brake fluid. He said he thought is was synthetic fluid originally in there because it was blue so he put in the silicone because it was blue too.

I dumped some fluid out of the sticky calipers into a cup, and added water. It absorbed completely.

I dumped some of his silicone brake fluid into another cup and added water. It beaded up and didn't absorb.

Is there any danger running silicone brake fluid? Will it attack the rubber in his new calipers and master cylinder? I heard it wasn't good as it expand allot when it gets hot and makes the brakes drag.

[cgarr]

I tried it years ago and never got a hard pedal with it so I went back to ate sb. I don't worry about water because it gets flushed each year anyhow.

[rob911]

my 84 had ATE super blue, better that the "regular stuff" in there now.

[HarryD]

I use ATE Gold/Blue.

Silicone brake fluid (DOT5) is used for folks who do not really care if the brakes are spongy. They are more concerned about the regular fluid absorbing water and corroding the system.

From Stoptech (http://www.stoptech.com/tech_info/wp_brakefluid_1a.shtml):

"what about the much touted Silicone based brake fluids? They are non hygroscopic and should take care of the reduced boiling point and corrosion problems. True! That’s the good news. That is why they are specified by the U.S. Military. Unfortunately the silicone based fluids are compressible themselves so they produce a soft pedal all by themselves. For the person who doesn’t care about a spongy pedal or precise modulation silicone fluids may well be the answer - but not for anyone reading this. In fact, low compressibility is a desired characteristic in a high performance brake system – lower compressibility results in more linear force output for driver input and improved driver feedback. "

[Steve@Rennsport]

One big problem with silicone brake fluids are incompatibility with glycol-based fluids.

If one switches to silicone fluid, one must properly & thoroughly flush the whole system with alcohol to get rid of all the glycol-based stuff otherwise you create a gummy mess and lose the non-hygroscopic qualities of the silicone version.

Due to its compressibility, its a very poor choice for any car that will be driven on the track, much less, raced. IMHO, its best suited for collector/museum cars that are rarely driven but must be preserved.

[James Brown]

Yes good point Steve, if you went with 5.0, flush and use 5.1 or good old 4 what Porsche and the master cylinder cap says.

[saurkraut]

I don't think he flushed it with alcohol before adding the silicon. So there is probably silly putty in the system now.

Will bleeding with standard brake fluid clear the mess?

[Green 912]

Big mess. the 5 will go after the brake light switches. part of the problem with 5 is it holds micro bubbles and it is the bubbles that give the soft feel not the pure fluid itself.
Best thing to do iIMO is rebuild the brakes from front to back MC, and all 4 corners. Flush the lines with low flash solvent and blow clear with clean dry compressed air. I cleaned a system of 5 and in the end the only way to get it all was to pop the pistons out and wash and blow everything clean.

[Steve@Rennsport]

Originally Posted by saurkraut

I don't think he flushed it with alcohol before adding the silicon. So there is probably silly putty in the system now.

Will bleeding with standard brake fluid clear the mess?

Nope,..the lines & MC must be flushed with alcohol and the calipers disassembled and cleaned with alcohol to deal with this properly. This is SOP before changing over to silicone fluid and back again.