Editing Drum brake (section)

==In operation==

===Normal braking===
When the brakes are applied, brake fluid is forced under pressure from the [[master cylinder]] into the wheel cylinder, which in turn pushes the brake shoes into contact with the machined surface on the inside of the drum. This rubbing action reduces the rotation of the brake drum, which is coupled to the wheel. Hence the speed of the vehicle is reduced. When the pressure is released, return springs pull the shoes back to their rest position.

===Automatic self-adjustment===
As the brake linings wear, the shoes must travel a greater distance to reach the drum. In systems fitted with automatic adjusters, when the distance reaches a certain point, a self-adjusting mechanism automatically reacts by adjusting the rest position of the shoes so that they are closer to the drum. Here, the adjusting lever rocks enough to advance the adjuster gear by one tooth. The adjuster has threads on it, like a bolt, so that it unscrews a little bit when it turns, lengthening to fill in the gap. When the brake shoes wear a little more, the adjuster can advance again, so it always keeps the shoes close to the drum. Typically the adjusters only operate when the vehicle is going in reverse and the brakes are engaged.

On vehicles without automatic adjusters, it is required to periodically manually adjust the brakes to take up any excess gap between the shoes and the drum.

===Parking/emergency brake===
{{Main|Parking brake}}
The parking (or emergency) brake system controls the brakes through a series of steel cables that are connected to either a hand lever or a foot pedal.  The idea is that the system is fully mechanical and completely bypasses the hydraulic system so that the vehicle can be brought to a stop even if there is a total brake failure. Here the cable pulls on a lever mounted in the brake and is directly connected to the brake shoes. This has the effect of bypassing the wheel cylinder and controlling the brakes directly.<ref>{{Citation |url= https://www.merriam-webster.com/dictionary/parking%20brake |title=Merriam-Webster Dictionary |quote= parking brake; Definition of parking brake :  emergency brake |date= 2017 }}</ref>