Originally Posted by
dedwards0323
[SIZE="2"]So you're hypothesis is that the brake fluid within the brake lines expands enough when heated that "free play" back to the pedal exists to prevent brake caliper closure & excessive pad/rotor wear due to dragging. Like James, I'm not sure I agree with this hypothesis as any thermal expansion of brake fluid from increased heat should be handled within the MC reservoir which has room for fluid expansion when filled to proper level. Is the brake system a closed system? In theory it is, but if there is a weak link it would be the MC cap which may or may not be an absolute seal. Are there check valves to prevent back flow to the master cylinder? Probably - To keep the brake lines full & minimize pedal travel when braking is required. There must be a pressure relief valve in the system to allow the pressure in the brake lines to reduce to a "steady-state" condition once the pedal is released, allowing the calipers to retract and excess brake fluid flows back to MC reservoir. And if this is the design, I can't see any force being applied to the MC actuator due to fluid thermal expansion. Gotta look at the brake system PFD to confirm. However, the viscosity should be impacted and that could contribute to a need for increased pedal travel to develop braking force pressure. Gotta think about that some more.
But I do agree with your second hypothesis. Increasing the size of the MC would have an adverse impact on required pedal travel to generate sufficient braking force.
Just thinking out loud.
There are one way valves in the MC, you prime the MC when you fit a new one and if the valves were not there the fluid would simply drain out of th MC making the priming a waste of time. Fluid gets past these valves to make up losses but cannot get back into the MC or the reservoir.