[Walt Fricke]

Stophos

You could try that. It should tell you if the reservoir vent has somehow become plugged. It won't quite test the whole system from inside the MC to the outside air.

It might be simpler - just take the reservoir off and check that everything which should be open is.

Or, if the MC is in place, blow (fairly gently - 10 to 20 psi should be enough) through an opened bleed valve on a caliper. Fluid (if the system hasn't been drained) should emerge from wherever this model has its overflow from the reservoir. In the SCs it is in front of the left front wheel.

I can't imagine that at least one pad on each caliper is sticking. Of course, I am taking his word that this is the case. Same with pistons sticking. But on rereading the post, I see that he has replaced the rubber hoses, and rebuilt all calipers (or at least checked their action), which makes the flap theory and the sticking piston theory moot. Plus he had the car, in its brakes stuck on condition, up on a lift and confirmed that all four wheels wouldn't rotate (or at least did so reluctantly).

The piston orientation on the single piston per side calipers is important, but only to pad wear. The cut-out part is intended to have the piston exert less pressure on the leading edge of the pad. Since this is where the friction/heat is greatest, reducing pressure there helps keep the pad wear even. Otherwise you get taper wear, and find that the leading edge is rather thinner than the trailing edge. Not sure this hurts braking, but it hurts the pocket book as you have to replace pads sooner. Besides, this is a 930 we are talking about, and it has 4 piston calipers. The leading edge piston is smaller in diameter than the trailing edge one to produce this differential pad pressure.

Mind you, I have no experience with the vent being blocked, and we have to assume that your new MC is good. Removing the actuating rod between the booster and the MC (if that is what was done) pretty much guarantees that the booster (with no relief of the unwanted residual pressure) is unlikely to have anything to do with this problem.