Air bubbles compress easily, making brake pedals feel soft and spongy. Bleeder valves allow you to purge this air. Located at the highest point of brake calipers or wheel cylinders, these screws have a hollow core with a small hole at the tip. When loosened slightly, fluid and air escape through the valve. Tightening it seals the system. Use a box-end wrench or a dedicated bleeder socket to prevent rounding the rusted hex corners.
Mechanic Glossary
Bleeder Valve
A threaded screw with an internal channel used to vent air or old fluid from hydraulic systems, most commonly found on brake calipers and slave cylinders.
Frequently Asked Questions
The small internal hole is likely plugged with rust or dirt. Remove the screw completely and clear the hole with a thin wire.
You must use a screw extractor to back out the broken piece or replace the entire caliper.
Start with the wheel that was worked on. If the brake pedal still feels soft, bleed the entire system starting from the wheel furthest from the master cylinder.
A small dab of anti-seize on the threads keeps them from rusting, but keep it clear of the tapered sealing tip at the bottom.