So 6 months or so ago I was frustrated by something in life and I vented my frustration sitting in the driveway by mashing down my brake pedal as hard as I could in a childlike tantrum fashion. Something I'd normally not admit on a forum LOL. But it was the foundation for the problem I'm having.

A mile up the road I noticed the brakes were feeling spongey.

I turned around to go home slowly and safely with half working brakes and by the time I got home the pedal was just going to the floor. At the fully-down position it would still hold my brakes fine to maneuver the vehicle in and out of the garage.

I figured it blew a seal in the 15 year old Master Cylinder and I finally got around to replacing the master cylinder a few weeks ago, and finally had time to bleed the brakes today.

During bleeding of the Front brakes I noticed that the pedal has 2 stages. The first half of travel, a kind of "click," and the second half of travel down to the floor.

When all brakes were fully bled, engine off, I thought it was weird that the pedal wouldn't harden. I could travel the pedal halfway down to just about where that "click" might happen, and then it was hard after that and wouldn't go to the floor.

I re-bled the brakes in case I missed some air. Nope no change.

So I thought I'd take it for a test drive and see how the brakes acted.

I started the car up and pedal went down to the floor exactly the way it had felt before I replaced the master cylinder!

So clearly the MC was not the culprit. But I'm not familiar with BMW's so I have no idea what else could possibly cause the pedal to hit the floor??? Zero resistance, just poof on the floor.

Brake fluid remains full in the reservoir and I don't see any fluid anywhere on the ground so I don't think it's dumping fluid anywhere. After bleeding I had pressure in the brake system. It was only after starting it again that it hit the floor.

The fact that the first stage of Master Cylinder travel never hardened up leads me to believe it's a problem in the rear half of the brake system perhaps?

Any input would be much appreciated. Thanks!

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2006 BMW X5, 3.0i - 161,000 miles
2003 Ford Mustang GT - because having Two cars that keep dying seemed more exciting.