Of all the ways to bleed brakes, gravity bleeding is the simplest - no pump, no helper, no special tools. You just open a bleeder and let physics do the work. It is handy in specific situations but has real limits. Here is how it works and when to use it.
How gravity bleeding works
You top off the master-cylinder reservoir, open one caliper's bleeder screw, and simply wait. Gravity pulls fluid down through the lines, and as it drips out the open bleeder it carries air with it. After a steady, bubble-free stream appears, you close that bleeder and move to the next wheel. It is slow but requires only one person.
When it is useful
Gravity bleeding shines when you are working alone and are not in a hurry, or as a first step to get fluid down to a dry caliper after a repair before finishing with another method. It follows the same wheel sequence logic as other methods - see the bleeding order chart. It is gentle and foolproof as far as it goes.
Where it falls short
Gravity alone often cannot clear every bubble, especially stubborn air trapped high in the calipers or in ABS units, and it will not build the pressure needed to firm up a fully air-filled system. For a truly solid pedal most jobs still finish with a pedal-pump (two-person) or vacuum/pressure bleed - see brake bleeding basics. Cars with ABS may need a scan tool regardless.
Do not let the reservoir run dry
The one critical rule: keep the master-cylinder reservoir topped up the entire time. If it drains while fluid drips out, you pull fresh air into the whole system and undo your progress. Watch it closely. Finish with fresh fluid and, if you are servicing brakes, quality pads and hardware.