I had a soft brake pedal,accompanied with a swooshing sound when applying the brakes. Bleeding did no good,so I replaced the master cylinder. Unfortunately nothing changed.I am able to pump the pedal with the ignition off,and it gets hard and holds. However as soon as I start the engine the pedal goes soft. Someone said that the culprit might be 1. Air trapped inside the ABS module or 2. Bad brake lines. I was careful to prime the new MC,and don't think air is trapped in the module,as the soft pedal was present prior to installing the master cylinder. Any suggestions. ..Thanks,Bob in Wichita.

 

Hi Bob,
Might be a good idea to determine where the swooshing sound is coming from. It could be normal sounds from the brake booster and maybe not.
Good idea to check all the vacuum lines coming to the booster.