A parking brake that lets the car creep on a hill, or a lever/pedal that travels much too far before it grabs, is one of the most common and most fixable brake complaints. Usually the mechanism just needs adjustment. Here is when and why - and how it is done.
Why parking brakes go slack
The parking brake works through a cable (or an electronic actuator) that clamps the rear brakes independently of the hydraulic system - see how the parking brake works. Over time the cable stretches and the rear shoes or pads wear, so the same lever pull produces less clamping. The result is excessive lever travel and weak holding.
Signs it needs adjustment
Tell-tale signs: the lever pulls up very high or the pedal goes nearly to the floor before it engages; the car rolls on a moderate incline with the brake set - see parking on a hill; or you count many clicks on a ratchet lever. If the brake holds but only at the very end of travel, adjustment is the fix.
How adjustment works
On cable systems there is an adjuster - often a nut under the center console, at the lever, or an equalizer under the car - that takes up cable slack until the brake engages within the correct range (commonly a few clicks). On drum-in-hat and drum rear brakes there may also be a star-wheel shoe adjuster inside. Electronic parking brakes are recalibrated with a scan tool, not a cable nut.
When it is not just adjustment
If adjusting does not restore a firm hold, the problem may be a seized or stretched cable, worn rear shoes/pads, or a stuck parking brake. Worn rear friction and hardware should be replaced - quality pads and fresh hardware restore both the service and parking brake.