Originally Posted by kenjisan

Conventional brake bleeding is entertainment.

Originally Posted by kenjisan

I have found that on cars with ferrous alloy calipers and aluminium pistons that corrosion is a problem if the cars are not driven often. This is cause from the water in contact with the dissimilar metals and causing a galvanic reaction. Many of the cars today have aluminium calipers and pistons so this problem is greatly reduced, not because of bleeding. Boiling is still the risk and many drivers dont work the brakes hard enough to reach the boiling temperatures . Anyone driving on the race track should avoid this risk.

There are a number of principles at work here. The hygroscopic ( attraction ) and colloidal ( suspension ). Both of these account for the water presents but they dont explain any kinematics (motion ).

Over time the water in the brake fluid will migrate to the lowest point. If you use a bottle to catch the old fluid from the caliper bleed screw and allow it to set on the bench long enough you can see this effect. I think that over the years to many people who bleed brakes dont look for this condition and feel they have solved the problem. If bleeding is done "frequently" the contaminated fluid " above " the bleed screw will have very little water to settle out. That doesnt reflect the fluid below the screw.

If you put some dirt in a water bottle and shake it up there will be a homogeneous suspension for a brief period and the heaviest particle will settle to the bottom. There will be some colloidal suspension of the lighter particals for a longer period. If a hole is made in the side of the bottle, above the heaviest particles, they will not run out with those above the hole.

Any steps to reduce the water in the space below the bleed screw is helpful but any water that remains will still be able to boil.

Conventional brake bleeding is entertainment.