Automotive Drum Brake Service (1258 views)
Automotive Drum Brake Service
Drum Brakes are comprised of a drum & backing plate, a hub or axle assembly, brake shoes , wheel cylinder, wheel bearings and hardware necessary to mount these components on the vehicle. The wheel cylinder is connected to the master cylinder through tubes, hoses and valves that conduct brake fluid through the system.
Drum brakes work on the same principle as disc brakes: Shoes press against a spinning surface. In this system, that surface is called a drum.
Many cars have drum brakes on the rear wheels and disc brakes on the front. Drum brakes have more parts than disc brakes and are harder to service, but they are less expensive to manufacture, and they easily incorporate an emergency brake mechanism.
Your car's braking system requires routine maintenance and should not be neglected - a life could depend upon it - maybe your own. Forces applied by the brake shoes against the brake drum generate substantial amounts of heat while applying frictional forces to the brake drums in order to bring your vehicle to a safe stop. Friction and heat wear out parts, meaning your car may not stop as quickly as it should - especially under a panic stop scenario.
The most common service required for drum brakes is changing the brake shoes. Some drum brakes provide an inspection hole on the back side, where you can see how much material is left on the shoe. Brake shoes should be replaced when the friction material has worn down to within 1/32 inch (0.8 mm) of the rivets. If the friction material is bonded to the backing plate (no rivets), then the shoes should be replaced when they have only 1/16 inch (1.6 mm) of material left.
Just as in disc brakes, deep scores sometimes get worn into brake drums. If a worn-out brake shoe is used for too long, the rivets that hold the friction material to the backing can wear grooves into the drum. A badly scored drum can sometimes be repaired by refinishing. Where disc brakes have a minimum allowable thickness, drum brakes have a maximum allowable diameter. Since the contact surface is the inside of the drum, as you remove material from the drum brake the diameter gets bigger.