Tech talks

The usual drum brakes in our car are provided with a remarkable feature called 'servo' or 'self energizing' feature. It is this feature that is responsible for the smooth and flat application of brakes in automobiles. When the vehicle is moving left, in the forward direction, then the drum will rotate in the anticlockwise direction. When the brake pedal is suddenly pressed, the two brake shoes at the drum will have full contact with the drum. However, one of the brake shoes, the primary brake shoe tends to slip for a certain distance in the drum's direction. Due to this, the primary brake shoe will tend to apply a rearwards force on the secondary brake shoe at the bottom. The wheel cylinder at the top forces the piston against the top of both the brake shoes. Due to this, the secondary brake shoe experiences force on both the sides i.e the top and bottom side.  This ensures that the brakes are applied uniformly and much less effort is applied.