How Does Brake Drums Work?
Brake drums play a very important role in the overall performance of your vehicles entire braking system. In this article we will explain what a brake drum is, what it does and hopefully everything else you will need to know about them.
Brake drums are usually found on the rear of vehicles, but prior to the late 60’s and early 70’s they were standard equipment as the front brakes as well. Brake drums are the friction point where the brake shoes contact to slow a vehicle. They vary in size depending on the application: large work trucks will use a larger drum brake, while passenger cars use a much smaller brake. Brake drums can be made of different materials such as cast iron, on some vehicles they have used aluminum to save weight and improve the cooling of the brakes.
Drum brakes are part of the overall car braking system which includes the brake pedal, master cylinder and front disc brakes. When the brake pedal is pressed, brake fluid under pressure flows through the brake lines and presses the drum and disc brakes against shoes and pads, causing both to make the rotor system bring the car to a stop.
Brake drums are also the emergency brake on most vehicles (with rear drum brakes). When the emergency brake is pulled (lever) or pushed (pedal), it uses a mechanical linkage and cable system to force the brake shoes out against the brake drums, holding the vehicle in place. Most vehicles with rear disc brakes have the inside of the rear rotor machined like a small brake drum, with a small set of shoes for the emergency brake.
When replacing a brake drum, it must be cleaned very thoroughly of all foreign coatings. Brake drums are coated after they are manufactured to prevent rust on the mating surface, this coating must be removed before installation or it will contaminate the brake shoes and cause performance issues or noise in the brakes. To clean any brake parts or mating surfaces, you can use an aerosol brake parts cleaner and a clean rag. Wear eye protection when using spray cleaners, they can spray back into your eyes and cause damage.
While disc brakes consist of a pair of calipers that squeeze brake pads against a rotor disc to cause friction, drum brakes consist of a pair of brake pads that extend outward and press against the inside of what is called the "brake drum." These pads are situated inside the drum. They are mounted on a "back plate," which in turn is attached to the axle and wheel. The cylinder is the part which expands to press the brake shoes outward.
When the pedal is pressed, brake fluid forces a cylinder on the top and bottom of the brake drum outward. The cylinder has double pistons, one to press on the brake pad on each side. This acts in the inverse way as a muscle does, expanding to cause pressure and push the pads against the drum. Both pads are shaped to fit the exact contour of the inside of the drum. So the pads create a lot of friction and force the car or truck to stop quickly. As such, these brakes are not as sensitive or performance minded as front side disc brakes. They are actually rarely used and only provide about 30 percent of everyday braking power.
Brake drums are usually found on the rear of vehicles, but prior to the late 60’s and early 70’s they were standard equipment as the front brakes as well. Brake drums are the friction point where the brake shoes contact to slow a vehicle. They vary in size depending on the application: large work trucks will use a larger drum brake, while passenger cars use a much smaller brake. Brake drums can be made of different materials such as cast iron, on some vehicles they have used aluminum to save weight and improve the cooling of the brakes.
Drum brakes are part of the overall car braking system which includes the brake pedal, master cylinder and front disc brakes. When the brake pedal is pressed, brake fluid under pressure flows through the brake lines and presses the drum and disc brakes against shoes and pads, causing both to make the rotor system bring the car to a stop.
Brake drums are also the emergency brake on most vehicles (with rear drum brakes). When the emergency brake is pulled (lever) or pushed (pedal), it uses a mechanical linkage and cable system to force the brake shoes out against the brake drums, holding the vehicle in place. Most vehicles with rear disc brakes have the inside of the rear rotor machined like a small brake drum, with a small set of shoes for the emergency brake.
When replacing a brake drum, it must be cleaned very thoroughly of all foreign coatings. Brake drums are coated after they are manufactured to prevent rust on the mating surface, this coating must be removed before installation or it will contaminate the brake shoes and cause performance issues or noise in the brakes. To clean any brake parts or mating surfaces, you can use an aerosol brake parts cleaner and a clean rag. Wear eye protection when using spray cleaners, they can spray back into your eyes and cause damage.
While disc brakes consist of a pair of calipers that squeeze brake pads against a rotor disc to cause friction, drum brakes consist of a pair of brake pads that extend outward and press against the inside of what is called the "brake drum." These pads are situated inside the drum. They are mounted on a "back plate," which in turn is attached to the axle and wheel. The cylinder is the part which expands to press the brake shoes outward.
When the pedal is pressed, brake fluid forces a cylinder on the top and bottom of the brake drum outward. The cylinder has double pistons, one to press on the brake pad on each side. This acts in the inverse way as a muscle does, expanding to cause pressure and push the pads against the drum. Both pads are shaped to fit the exact contour of the inside of the drum. So the pads create a lot of friction and force the car or truck to stop quickly. As such, these brakes are not as sensitive or performance minded as front side disc brakes. They are actually rarely used and only provide about 30 percent of everyday braking power.
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