Bleeding the brakes is the process of pushing fresh fluid through the system to remove trapped air. Because air compresses and brake fluid does not, even a little air gives a soft, spongy pedal. Bleeding restores a firm pedal and full braking. Here are the basics.
When you need to bleed
- After opening the hydraulic system - replacing a caliper, hose, line, or master cylinder.
- After a brake fluid flush, to move fresh fluid through - see our fluid flush guide.
- Any time the pedal is soft from air in the lines - see spongy pedal causes.
Common methods
- Two-person: one pumps and holds the pedal while the other opens and closes the bleeder screw at each wheel. Simple and effective.
- Vacuum bleeding: a hand vacuum pump draws fluid and air out through the bleeder.
- Pressure bleeding: a tool pushes fluid through from the reservoir under pressure.
- Gravity bleeding: open the bleeders and let fluid drip out slowly on its own - slow but low-effort.
The right order
Follow the sequence in your vehicle's service manual. Many vehicles bleed starting at the wheel farthest from the master cylinder and working closer, but modern ABS-equipped vehicles often specify a particular order - and some require a scan tool to cycle the ABS module. Always check the manual.
Key tips
- Never let the reservoir run dry mid-bleed, or you pull air back into the system.
- Use fresh fluid of the correct DOT rating - see our brake fluid guide.
- Keep brake fluid off paint - it is corrosive.
Bleeding is often part of a bigger brake job. Start with the right pads and hardware, and if you are not confident working on the hydraulic system, have a professional do it - brakes are safety-critical.