Car drum brake components and functions (leading trailing type)
What is drum brake? Drum brakes are brakes that use drums and brake linings as braking friction media to reduce the rotation speed of the wheels. Drum brakes are commonly used on the rear wheels of passenger cars, and they are more widely used on heavy load vehicles such as trucks or buses. One of the advantages of drum brakes is that the braking power is stronger because the friction area is greater than the disc brakes.
Drum brakes have several types and models, such as the two leading types, leading trailing, duo servo, uni servo and many others. However, some of the drum brake components still have the same parts name and functions.
So, what are the components of the brake system, mostly for the drum brake type? The following post contains information about the various drum brake components that we know. Read the leading-trailing type drum brake components below.
1. Wheel cylinder
The first component of the car drum brakes is the wheel cylinder. A wheel cylinder is located in each wheel. It is usually positioned at the top of the wheel, above the shoes. The wheel cylinder function is to exert force onto the shoes to contact the drum and stop the vehicle with friction.
Wheel cylinder consists of several components such as:
- Wheel cylinder housing; is a place for all wheel cylinder components, including brake oil
- Pistons; The drum brake pistons function is to change the hydraulic pressure to be mechanical movement. They are connected to the brake shoes.
- Piston seal cups; The piston seal cups function is to keep the hydraulic pressure of brake oil from leaking.
- Piston boots; The piston boots function to protect the pistons from dust and debris and prevent rust.
- Return spring; Returns spring function is to bring the pistons back to their positions, so the pistons are always in contact with the brake shoes.
- Bleeder nut; The bleeder nut functions as an air drain from the wheel cylinder, so the wheel cylinder is filled only by brake fluid.
2. Backing plate
The second component of the car drum brakes is a backing plate. The backing plate is made from a steel plate with a circular design. The function of the backing plate is to hold the braking system together so it can work properly.
It holds almost all drum brake components such as wheel cylinder, brake shoes, anchor, adjusting lever, etc. The backing plate is attached to the differential housing or knuckle arm and being a stationary component.
3. Pins
The third component of the car drum brakes is pins. The pins work together with shoe hold springs to hold the brake shoe so they can always stick to the backing plate as a holder.
4. Parking lever
The fourth component of the car drum brakes is the parking lever. The parking lever is a lever that will activate the brake shoes manually using a brake cable. When the driver pulls up the parking brake lever inside the car cabin, the parking lever will move and push the brake shoe manually. So the brake shoe pushes the drum brake and makes the parking brake active.
5. Anchor
The fifth component of the car drum brakes is the anchor. The anchor is fitted on the backing plate and has an opposite position to the wheel cylinder. The anchor function is as a base and pivot for the end side of the brake shoe when they're moves. There are two types of anchor models, fix type model and moveable type.
6. Brake shoe & linings
The sixth component of the car drum brakes is the brake shoe and lining. Brake shoes and linings are the main components were used to slow or stop the car. They are pushes into the drum to create friction. Secured to the backing plate but able to slide when pressure from the wheel cylinder is applied.
The linings are made up of organic or metallic compounds. The lining is what comes in contact with the drum and wears away with use. Each brake contains two shoes. The primary shoe is closer to the vehicle's front, while the secondary shoe is closer to the rear.
Read also:7. Adjuster lever
The seventh component of the car drum brakes is the adjuster lever. The adjuster lever function is to adjust the gap between the brake shoe lining and the inner side of the drum. The gap is affecting the brake pedal play.
Automatic adjusters adjust the gap by themselves, keeping the brake shoes at a consistent distance away from the drum. Still, if your drum brake uses a regular adjuster type, you need to adjust the gap regularly. So if your brake pedal play is too large, then to reduce the length of the brake pedal play, adjust this adjuster lever.
8. Drum
The eighth component of a car drum brakes is a drum. The drum is often made of cast iron and is resistant to heat and wear. It bolted to the wheel hub and spun with the wheel. When a driver applies the brakes, the lining pushes against the inner surface of the drum. The ensuing friction slows or stops the rotation of the wheel and axle, and thus the vehicle.
9. Shoe hold spring
The ninth component of the car drum brakes is the shoe hold spring. Shoe hold spring function is to keep the brake shoes always fitted to the backing plate. The springs work together with pins.
10. Return spring
The last component of the car drum brakes is the return spring. Return spring serves to retract the brake shoe & lining position after the braking process takes place, mostly when the driver lets off the brake pedal.
When the brake pedal is pressed, the brake shoe will move outwards and press on the brake drum due to piston pressure in the wheel cylinder. And to prevent the brake shoe from continuously pressing the brake drum, this return spring is used to return the brake shoe to its original position.
The location of the return spring is generally 2: above (upper spring) and at the bottom (lower spring). In addition, the two return springs are generally installed between the two brake shoes.