Master cylinder location question 8

[dwaldron]

I installed disc brakes on a small machine...lack of space forced me to locate the MC below the calipers. I'm having a hell of a time getting the air bled out of the system. I understand that a fix would be to move the MC above the calipers...but I can't do that...so would a fix be to locate the MC reservoir remotely and above the calipers?

Dan

 

[MikeHalloran]

The problem with any fluid that doesn't absorb water, as has been noted, is that water accumulates in the low points of the system.

What may not be obvious from that statement is that the accumulated pools or tiny drops of water become corrosion cells, and eat pinholes right through otherwise perfectly good metal.

A single pinhole can quickly drain the entire trapped volume of fluid upon which the brake system depends, either in storage or upon first application.

In a hydraulic system, normal operating flows will sweep away small volumes of accumulated water, or at least move them around so they don't always eat the same piece of metal. In a brake system, the fluid moves only upon application, doesn't move very far, and upon retraction comes back to where it was before, so the water is always in the same place, eating the same metal.



Mike Halloran
Pembroke Pines, FL, USA

 

[swall]

The viscosity vs temperature relationship of mineral oil hydraulic fluids was considered unacceptable at the time when hydraulic brakes were first developed. Various combinations of caster oil, alcohol and other stuff was tried before the industry finally settled on the glycol base brake fluids. Mineral oil based hydraulic fluid did find its way into the brake system of one Citroen model, which had a central hydraulic system for other functions. Military aircraft use mineral oil in the brake systems whereas commercial aircraft use the phosphate ester fluids (Skydrol). I think that silicone brake fluids mainly came into being because a major U.S. maker of silicone was looking for potential markets for the stuff.