The caliper or wheel cylinder action doesn't directly control the amount of friction generated by the brake lining. Instead, the action of the caliper or wheel cylinder controls the physical contact between the brake linings and the rotating components (brake rotor or drum), allowing or limiting the amount of friction that is generated. The friction itself is a result of the natural interaction between the brake lining material and the rotating surface.

Here's how the caliper or wheel cylinder action influences the friction generated by the brake lining:

Caliper Action (Disc Brakes):

When you press the brake pedal, hydraulic pressure is applied to the caliper, causing the caliper pistons to move.

The movement of the caliper pistons pushes the brake pads against the brake rotor. The friction material (brake lining) on the inner side of the brake pads comes into contact with the rotor's surface.

The contact between the brake lining and the rotor generates friction, which slows down the rotation of the wheel. The amount of friction generated depends on factors like the pressure applied to the brake pedal, the coefficient of friction of the brake lining material, and the condition of the rotor's surface.

Wheel Cylinder Action (Drum Brakes):

Hydraulic pressure is applied to the wheel cylinder when you press the brake pedal, causing the wheel cylinder pistons to move.

The movement of the wheel cylinder pistons pushes the brake shoes against the inner surface of the brake drum. The friction material (brake lining) on the curved side of the brake shoes makes contact with the drum.

The contact between the brake lining and the drum generates friction, which slows down the rotation of the wheel. Again, the amount of friction generated depends on factors such as hydraulic pressure, brake lining material, and the condition of the drum's surface.

In both disc and drum brake systems, the caliper or wheel cylinder action controls the extent to which the brake linings come into contact with the rotating components. The more force applied by the pistons, the greater the contact and thus the greater the friction generated. Conversely, releasing the brake pedal reduces the force exerted by the pistons, reducing the contact and friction.