Q – My 993 has a soft brake pedal. If I push it down and hold it, it slowly sinks half way down. The odd thing is that when I stored it in the fall, the brakes felt fine! I took it to a shop that diagnosed it as a failed master cylinder. I had them replace the master cylinder and now they are telling me that they think the ABS pump unit has an internal leak and that is why the pedal is soft. The part alone is $2,700! The master cylinder was not cheap and this “spring surprise” has really dampened my enthusiasm for the car. I have to wonder if they really know what they are doing. – Peter
A – A soft brake pedal can be caused by a failed master cylinder but before condemning it, a proper brake inspection should be done to be sure that no leaks or other sources of pressure drop could be causing the symptom. This inspection should include checking tightness of all the fittings in the system especially the fittings on the ABS pump. Usually Porsche tightens brake fittings very, very tight but once I found a loose fitting on the pump that caused a soft pedal.
Following the inspection, I would then pressure test the system caliper by caliper to verify the diagnosis. Expect to measure about 1,000 psi while pressing and holding the pedal down with moderate force. If you find a drop in the front or rear circuits, if it were my call, I would replace the master cylinder to eliminate that as a possibility and then see if pressure drop still occurred. Although this is a painful method of diagnosis, I know of no other way to eliminate the master cylinder as the source of the problem. You cannot condemn the ABS pump unit without a known good master cylinder in the system. – MC