You need to make sure that your brake pedal is returning fully, and not being obstructed in some way, e.g. by a stiff pivot, or badly adjusted brake light switch (only one type was adjustable, the other mechanical type was not, and early ones were hydraulic), or even the carpet. The master cylinder push rod must be slack when your foot is off the pedal, otherwise at least one reservoir port will not be uncovered, and one of the circuits will not bleed, and will also have brakes that sieze on as they get hot, because it can't vent pressure back to the reservoir. Swollen master cyliner seals can also cause the same problem, if so you must overhaul ALL the hydraulics as the cause is usually due to oil in the system, and the slightest trace will make it happen again.
As you seem to have a servo, consider the implications. I have described what happens if the pedal is not returning fully, however your servo is between pedal and master cylinder so it adds another thing that can result in the same situation. If the servo has an internal fault, maybe a vacuum leak, and instead of being fully retracted by the large internal spring, it is trying to push the master cylinder slightly, you will see that the same thing will happen.
The other possibility is degradation and internal blockage of the front hoses.
I would first try the Eesibleed with the master cylinder loosened from its mounting so that there is no possibility of the piston being pressed. If fluid bleeds through the system ok, the cause is established as pedal or servo.
If not, then loosen the master cylinder outlets, one at a time, to check if fluid is coming through. If not, it is an internal master cylinder fault. Strip, check for swollen seals, and if so, renew every rubber seal and hose in the system, flush the rigid pipes with compressed air until dry, (or fit new Kunifer pipes), fill with fresh fluid, and bleed. With a fluid change every 18 months, it will last for a while....
Edit: lrostoke may be correct, and if so, throw the valve away and get a new one. However, it is "supposed" to only be able to block the rear brakes under hard braking, based on the pressure in the front circuit, which passes straight through.
Edited by tiger99, 16 May 2013 - 08:57 PM.
