<VV> was synthetic oil, now silicone brake fluid

[CorvairEd at aol.com]

In a message dated 7/6/05 2:18:25 PM Pacific Daylight Time, 
Corvair at fnader.com writes:
Moisture can enter the system in lots of ways. First and foremost is in the 
air suspended in the fluid. Silicone fluids carry much more air than glycol 
fluids, so while the fluid doesn't actually attract moisture like glycol does, it 
already carries more when fresh.

Moisture can also enter through microscopic pores in soft brakes hoses and 
seals, cracks/leaks in the hoses or lines, air that is drwn into the resevoir as 
the pads or shoes wear, and each time you open the master to check the fluid 
level.

OK, if there is air suspended in the silicon fluid with moisture in it why 
does the moisture not settle out to the bottom of the DOT 5 bottle?  Remember 
water will not mix with silicon fluid.  If there are microscopic pores in soft 
brakes hoses the fluid would leak out when you press real hard on the brake 
pedal.  Also, air is not drawn into the reservoir as the pads or shoes wear 
because there is an accordion boot under the master cylinder cover that expands if 
the level drops and keeps air from being drawn in.  The amount of time that 
the cover is off of the master cylinder to check the fluid level is minuscule 
and is not long enough to allow moisture in, unless you check the fluid out in 
the rain.  Face it, how many times a year do you check the fluid level?  With 
silicone fluid in a sound brake system there is no loss from evaporation in the 
life of the system.  With disk brakes as the pads wear down the fluid level 
does drop slightly but you should not add fluid because when you replace the 
pads the fluid level will be pushed back to its original level and if you added 
fluid the master cylinder would be over filled and malfunction.

As far as there being a problem with hot brakes under hard use like racing, 
my son and I both autocross with silicon fluid and the brakes get so hot the 
smell and smoke with no problems.  NASCAR racers don't use silicon because their 
brakes actually get red hot for an extended time and that is another matter.  
They also don't use DOT 3 because of the extreme heat.

Ed Corson (CORSA member)
Inland Empire Corvair Club