Hello mechanical friends, in this article we will share information about the types of drum brakes in cars, please read to add to your insight in the automotive world. In general, drum brakes are divided into two groups, namely: Non-servo drum brakes and servo drum brakes.
a. Non-servo drum brakes.
Non-servo drum brakes are used on smaller vehicles, with front-wheel drive. In this vehicle, the rear brake receives only a fraction of the braking load and can be designed to be simpler. Non-servo brakes use the same type of wheel cylinder as a brake shoe suppressor. Wheel cylinder pressure pushes both brake shoes out. The front shoe is self-energizing because it is influenced by the rotation of the drum (movement of the brake shoe in the same direction as the drum rotation) is called the primary or leading brake shoe. However, the rear brake shoe presses the drum and is opposite the direction of the drum rotation so it does not have self-energizing. The rear brake shoe operates only with the hydraulic pressure of the rear wheel cylinder. If the vehicle moves backward, the opposite happens.
* Leading-Trailing
The working of the leading-trailing drum brakes is much simpler than in other systems. When the brake pedal is depressed the wheel cylinders push with the same pressure on each brake shoe. In turn, this forces the top of each outer shoe towards the drum, and each brake shoe resting on an anchor located at the bottom of the backing plate.
The friction of the drum pulls the leading shoe so that it will be stronger pressing the drum which is the assisting force on the wheel cylinder.
The secondary shoe is not self-energizing so it does not provide additional braking force to the wheel cylinders.
When the drum rotates in the opposite direction, it will be the opposite. In leading-trailing systems, primary and secondary brake linings are usually the same shape and size.
* Two Leading / Duplex.
Two leading non-servo drum brakes are used on small or large vehicles on the front wheels. The front-wheel brakes receive an additional part of the rear wheel load when the vehicle is the brake. The wheel cylinder pressure pushes the two brake shoes out.
If the drum rotates towards the forward direction of the two brake shoes, there is self-energizing because it is influenced by the rotation of the drum (movement of the brake shoe in the same direction as the drum rotation), both of them become leading/primary shoes.
However, when the drum rotates backward, the two brake shoes become trailing / secondary all because they are in the opposite direction to the rotation of the drum so they do not have self-energizing. When the vehicle is moving backward, the two brake shoes work only with the hydraulic pressure of the wheel cylinder.
In a two-leading system, primary and secondary brake linings are usually the same shape and size.
The duo two leading drum brakes are almost the same as the two leading type, but the two leading duo type uses two-wheel cylinders each with two pistons so that all brake shoes have a self-energizing effect, both the vehicle is moving forward and backward.
* Duo two leading.
b. Servo drum brakes.
In servo-brakes both the primary and secondary shoes contribute to the braking process. The servo brake system uses a single-piston (servo) wheel cylinder piston (servo) or uses a wheel cylinder with a dual piston (duo servo), which is attached to the top of the backing plate. The bottom of the brake shoe (brake shoe mount) is not attached to the backing plate. Instead, the shoes are connected via a floating star wheel adjuster.
* Servo drum brakes (single piston wheel cylinder.)
When the brake pedal is depressed, both shoes are forced out against the rotating brake drum with the wheel cylinder piston. When the primary shoe presses into the drum, it is affected by drum rotation.
This rotation is transmitted to the secondary shoe via a floating star wheel adjuster.
This power of transfer is called servo action.
The Servo action causes the secondary shoe to move because the other end is caught by a stopper, the brake will become stuck. The self-energizing effect will appear on both brake shoes when the vehicle is moving forward, whereas when the vehicle is moving backward, the two brake shoes do not have a self-energizing effect.
* Drum brake duo servo (two-piston wheel cylinder)
The way the duo servo drum brakes work is the same as the servo-type drum brakes with the difference being: The duo servo type uses a wheel cylinder with two pistons so that either the vehicle moves forward or backward the self-energizing effect will appear on both brake shoes.
Vehicle Safety Standards require that the parking brake is capable of holding the vehicle to a stop at a slope of 30 degrees. The parking brake system in most vehicles is operated by hand or foot, the parking brake works on the rear wheels.
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