Joerg wrote:
:On 2018-06-11 08:39, David Scheidt wrote:
: Joerg wrote:
:
: :Water in DOT boils out. That's what happens in the open systems on motor
: :vehicles. Unfortunately bikes don't have those but if you were truly
:
: What motor vehicle has a brake system open to atmosphere? It ain't
: the fifties, man. They're sealed systems. Have been for decades.
:


:What do you think that little hole is for?

What do you think the diaphragm is for?

:https://i.stack.imgur.com/lFHT8.jpg

That's a cap for a clutch master cylinder, but the principal is the
same. the rubber diaphragm is in contact with the fluid, kepeing the
system sealed. the hole in
the cap lets the air in and out of the air space between the air tight
rubber gasket and the cap. That lets the fluid level flucuate with
temperature or air pressure changes, etc, while still keepoing a
sealed system. Brake systems open to the atmoshpere went out with the
60s.

Bikes, by the way, use the same system:
https://www.parktool.com/assets/img/...gure_11-12.jpg


: Brake fluid
: in motor vehicle systems is not recirculated much, and the the fluid
: that's in the calipers tends to stay in the calipers. It is not at
: all unusual to discover a caliper is full of water, while the fluid at
: the master cylinder is normal.
:

:That would be a vehicle in a very harsh state of neglect. Probably sat
:in a yard for a couple of decades. Water is supposed to mix with the
:brake fluid which is why that's DOT and not oil. This lowers the boiling

Brake fluid only carries a small amount of water, when that is
exceeded, you have water and water-logged brake fluid. Because there is
very little actual movement of fluid in conventional juice brakes, if
the fluid in the caliper is overwhelmed, it seperates out, even if the
amount of water involved is low enough the fluid volume of the whole
system would carry it. It requires neglect or abuse, but I've seen it
on working trucks.


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