When you say a master cylinder is biased, are you saying you get different pressure out of one line VS another? Is that possible?
I don't think it is.
When a car is designed, the size of pistons front or back gives the manufacturer the calculated brake capabilities.
And that factory valve that most call a proportioning valve is not that at all. It is a shuttle valve that gives you the dual/failure mode braking if front or back leak/fail. This is not done in the master cylinder.
I've been wrong before, so I am correctable, eh?
I will post a pic of a typical pre abs combination valve. Im doing this from an iphone so may not work😀
Most cars built from say ‘72 and later had valves with these features. First, yes, a shuttle valve to lock off a circuit failure, and indicate to the driver that there is a failure (warning light)
Next, the rear proportioning accumulator section.
Also note the front circuit has a spring loaded restrictor. This feature assures the rear circuit starts to react first. Mostly to take up slack in the rear shoe adjustment without shifting the shuttle section of the valve.
It is termed a combination valve because it has 3 functions. To say it is not a proportioning valve at all is a stretch.
As for not believing that a master cylinder can output 2 different pressures, that’s fine with me😂
