A brake pedal that sinks slowly - or drops straight to the floor - is one of the most serious brake problems you can have. It means the hydraulic system is not holding pressure. Treat it as an emergency. Here is what causes it and what to do.
What to do right now
If your pedal is going to the floor while driving: stay calm, pump the pedal to try to build any remaining pressure, downshift to let engine braking slow you, and use the parking brake gradually to help stop. Get off the road safely and do not keep driving. Have the vehicle towed and inspected - this is not a fault to nurse home.
Likely causes
- A brake fluid leak. A leak at a caliper, wheel cylinder, hose, or line drops system pressure so the pedal sinks. Check for a low reservoir or fluid on the ground.
- A failing master cylinder. Internal seals can bypass, letting the pedal slowly sink to the floor under steady pressure even with no visible leak.
- Air in the lines. Air compresses, so a system with air gives a soft pedal that can travel far - see spongy brake pedal causes.
- Badly overheated fluid that has boiled - see our brake fluid flush guide.
Soft vs all-the-way-down
A slightly soft pedal deserves prompt attention. A pedal that goes all the way to the floor means you have lost most braking - do not drive it. The fix depends on the cause: repair the leak, replace the master cylinder, or bleed out the air, then flush with fresh fluid.
Prevent it
Flush brake fluid on schedule, replace worn pads and cracked brake hoses before they fail, and address any soft-pedal warning early. Brakes are safety-critical - when in doubt, have a professional inspect the system.