Once automobiles employed front and rear drum brakes. Because disc brakes are more effective, they replaced front drum brakes. Many vehicles still feature rear drum brakes, but all vehicles feature front disc. Nowadays many vehicles are replacing rear drum with rear disc, and the future of braking systems threatens the existence of drum brakes altogether.
Effectiveness
Rear drum brakes apply 20 to 25 percent braking capacity for any vehicle. One major problem with them is the self-adjustment they require. Drum brakes can easily become less effective when their adjustment falls below the normal standard. This places undue stress as well as more wear and tear on the front brakes.
Many imports that employ rear drum brakes featured a unique self-adjusting system, unlike domestic vehicles. However, in order to activate the feature, parking brake mechanisms had to be used.
How They Work
Rear drum brakes begin with a hydraulic wheel cylinder with internal bores that extend and retract upon demand. When they extend under normal braking, the bores protrude from the internal cylinder and extend the shoes outward to contact the internal perimeter of the drum, thus applying the friction material against the steel drum. Return springs provide replacement of the shoes away from the drum when the demand is no longer necessary.
The components and intricate drum braking system require all parts to cooperate. Because they only perform much less than half the braking power, they can easily deteriorate when not maintained.
Rear drum brakes are much more challenging to replace than disc brakes and require knowledge, reference and hand and finger dexterity to do so successfully.
Hydraulics
Rear-wheel cylinders control the hydraulics of rear drum brakes. If the cylinders or rear-axle seals leak petroleum-based fluid inside the drums, the shoes will become contaminated and require replacement. Wheel cylinders can seep hydraulic fluid after normal wear and tear and should be replaced before they contaminate other components.
Like pistons inside calipers of disc brake systems, wheel cylinder bored can seize internally, causing more wear and tear on front disc braking systems. When the rear brakes are not supplying their required braking capacity, although it may not even be noticeable to the driver, the front brakes overcompensate. This causes premature wear and damage to the front brakes.
Parking Brake
Rear braking systems--drum or disc--integrate the parking brake mechanisms. To properly maintain the rear drum brakes, it's important to apply the parking brake every time you park the vehicle. This procedure keeps the internal parts of the parking brake mechanisms moving and aides in keeping the rear drum brakes adjusted. It also manually positions the parking brake shoe against the drum, moves the self-adjuster cable (when applicable) and the self-adjuster mechanism. By keeping these components moving in the rear drum braking systems, they will continue to move freely when the hydraulic demand is placed on them.
Rear disc brakes feature rear caliper to parking brake connections. So even if you have rear disc brakes, although it may not aide in keeping the rear brakes adjusted, using the parking brakes will certainly help the longevity of the parking-brake system, which is required to be functional for most state inspections.
