Unlike disc brakes, drum brakes need occasional adjustment to keep the shoes the right distance from the drum. As the shoes wear, that gap grows and the brakes feel weak until re-adjusted. Here is when and how drum adjustment works.
Why drums need adjusting
In a drum brake, curved shoes press outward against the inside of a spinning drum - see drum vs disc brakes. As the shoe friction material wears, the shoes sit farther from the drum, so the wheel cylinder must push them farther to make contact. That extra travel shows up as a low brake pedal and weak rear braking until the gap is taken up.
Signs they need adjustment
Tell-tale signs: a low or long brake pedal - see brake pedal travels too far - weak rear braking, or a parking brake that pulls up much too high before it holds. Since the parking brake often works through the rear drums, a slack parking brake can mean the drums need adjusting too - see parking brake adjustment.
How adjustment works
Most drum brakes have a star-wheel adjuster between the shoes. Turning it spreads the shoes closer to the drum, taking up the gap. Many vehicles have self-adjusters that ratchet the star wheel automatically (often when braking in reverse), but these can seize with rust and need manual adjustment. You access the star wheel through a slot in the backing plate.
When to replace instead
If adjusting does not restore a firm pedal, the shoes may be worn out or the self-adjuster seized - time for new shoes and hardware; see brake shoes vs pads. Keep the whole system healthy - the front disc brakes take most of the load, so fit quality pads and hardware there too.