4 answers
★ Best answer
don't panic and don't brush off the problem thinking it'll fix itself 😸 air in the lines is really the most common cause, but before you bleed them check your brake pads too: if they're worn down the system compensates by sinking to maintain contact, which can feel like air even if it isn't. once you've ruled out wear, bleeding becomes pretty much mandatory and you're good to go.
Start with bleeding the brakes, period. If your brakes are sinking and feel spongy, 90% of the time it's air trapped in the lines. The procedure is straightforward: open the brake fluid reservoir under the hood, check that the fluid is at the right level, then go to the wheels (usually you start with the one farthest from the tank) and bleed each caliper with an appropriate wrench while someone presses the pedal from inside the car.
If nothing's changed after bleeding, it could be that your brake fluid is old and has absorbed moisture, which makes it compressible. In that case the solution is to flush the whole system. Also do a visual check of the hoses: if they're swollen, cracked, or have even tiny leaks, air gets in or fluid leaks out. A tiny leak you don't see when you take the wheel off usually shows up while you're driving because the brake pedal gets spongier and spongier over the last few miles.
If nothing works after all this, the problem might be in the brake master cylinder, but that's rare. Before you take it to a mechanic, try bleeding at least once: it's something you can learn in twenty minutes and it saves you money most of the time.
I had the same problem a few months ago: brakes that kept giving way and the pedal getting longer and longer. I first tried checking the fluid level, everything was fine, then I did a bleed starting from the cylinder furthest from the pump (rear) and after two cycles the air came out. If the air is really stuck in there, sometimes you need a little pressure on the pedal while you open the bleed valve, that forces everything out. Maybe it's not the most elegant method but it works, and after that you don't have those soft brakes anymore that give you anxiety in the corners.
What nobody mentions is that if air keeps coming back after bleeding, it could be a leak in the system and not just trapped air. I've seen people bleed the brakes three times and not understand why they stay soft - they eventually find a microscopic crack in a line or a seal that's not holding. If the pedal keeps sinking after you've gotten the air out, you can't fix it yourself and you need a more thorough inspection.
Your answer
Log into answer.