Spongy VW Brake Pedal Signals Dangerous System Issue

Had the exact same brake pedal issue on my 2011 VW Passat diesel last season. From my repair experience, a soft, sinking brake pedal usually indicates either air in the brake lines or a failing master cylinder, both serious safety concerns requiring immediate attention. The brake system symptoms match what you describe, pedal gradually sinking with minimal resistance. In my case, the master cylinder was leaking internally, not maintaining proper pressure in the hydraulic system. This affected both the disc brakes and overall brake performance. Given the age and mileage of your Eos, its likely facing similar hydraulic brake system problems rather than just worn brake pads or brake shoes. The master cylinder tends to start failing around 100000km in these VW models. This isn't a repair to postpone or attempt DIY since it affects your primary safety system. When the pedal goes soft, its warning you that brake failure could be imminent. Would strongly advise getting it inspected by a certified shop that specializes in brake systems. The fix typically involves replacing the master cylinder and bleeding the entire brake system to remove air. Some shops may recommend replacing brake fluid and inspecting brake lines while the system is open.

Thanks for the detailed explanation of the master cylinder issue. Your symptoms indeed sound identical to what I experienced. After having it fixed, my brake pedal is firm again and the brakes work perfectly. Mind sharing roughly what you paid for the complete brake system repair? Curious if prices have changed since then. Did they find any other worn components like brake rotors while doing the work? My repair has held up well but I make sure to have the brake fluid checked regularly now since these hydraulic issues can creep up again with age. Let me know how yours turns out if you get it looked at.

Happy to report my repair has been solid since fixing the brake system issues. The worn brake pads and faulty master cylinder were both addressed, and the brake pedal firmness remains perfect after several months. The total repair came to 240€, which covered parts and labor to resolve the undervoltage problem that was actually causing the brake system malfunction. Initially thought it was the master cylinder, but the mechanic found the electrical issue was affecting the brake calipers and overall hydraulic pressure. During inspection, they checked the brake rotors and remaining components, all were within spec and didn't need replacement. The brake fluid was also tested and thankfully didn't require changing. Good call on regular brake fluid checks. Maintaining proper fluid levels and condition is crucial for preventing these hydraulic brake issues from developing again. The repair has completely resolved that unsettling sinking pedal feeling, and braking performance is back to factory specs.

Thanks for the helpful advice. Just wanted to update on how my repair went. Took it to a certified brake specialist yesterday who diagnosed a failing master cylinder, exactly as suggested here. The total came to 380€ including parts and labor for the master cylinder replacement. While they had the hydraulic brake system open, they found one brake caliper was also starting to stick, so I had them replace that too. Better to fix it all at once. The mechanic flushed and bled the entire brake system with fresh fluid. They also inspected the disc brakes and brake lines, fortunately everything else checked out fine. What a difference in brake pedal feel now, firm and responsive like it should be. No more scary sinking to the floor. The shop even showed me the old master cylinder parts to explain the internal wear. Really glad I got this fixed before it became a complete brake failure. Having dealt with ripoff shops before, I felt the price was fair for the work done. Will definitely stay on top of brake fluid maintenance going forward.