Foot Brake Disc Brake


1. Construction

The disc brake consists of the following components.

(1) Disc brake caliper

(2) Disc brake pad

(3) Disc brake rotor

(4) Piston

(5) Fluid

2. Operation

The disc brake pushes the piston using the hydraulic pressure transmitted via the brake line from the master cylinder to cause disc brake pads to clamp down on both sides of the disc brake rotor and stop the tires from turning. Therefore, because the disc brake rotors and disc brake pads rub against each other, frictional heat is generated at this time. However, because the disc brake rotor and brake body are exposed, the generated frictional heat can be easily dissipated.

3. Brake Adjustment

Since the brake clearance is adjusted automatically by the piston seal (rubber), the brake clearance need not be adjusted by hand. When the brake pedal is depressed, the hydraulic pressure moves the piston and pushes the disc brake pad against the disc brake rotor. As this time, the piston moves while causing the piston seal to change shape. When the brake pedal is released, the piston seal returns to its original shape, which moves the piston away from the disc brake pad. Therefore, even if the disc brake pad is worn down and the piston is moving, the amount that the piston returns is always same, so the gap between the disc brake pad and disc brake rotor is maintained at a constant distance.

4. Decrease in brake fluid

The amount of brake fluid in the brake reservoir tank is decreased by the wearing of the disc brake pad or lining. Therefore, the wearing condition of the disc brake pad or lining can be estimated by checking the fluid level of the reservoir tank. Due to the piston’s large diameter, wearing of the disc brake pads results in a greater drop in the fluid level in the reservoir tank than in the case of drum brakes.

5. Pad wear indicator

When a disc brake pad wears and needs to be replaced, the disc brake pad wear indicator generates a highpitched screeching sound to alert the driver. In the case of the Corolla, the warning occurs when the actual pad thickness is approximately 2. 5 mm (0. 098 in). (1) Construction and Operation When pad thickness is reduced to the above-mentioned thickness, the pad wear indicator, fixed to the backing plate of the pad, comes into contact with the disc brake rotor and produces a screeching noise during driving.


There are sensor type pad wear indicator brakes like that shown at the bottom left of the figure. When the sensor is worn down together with the disc brake pad, the sensor’s circuit is opened. The ECU detects the open circuit and warns the driver.

6. Types of disc brake caliper

The types of calipers are explained below. (1) Fixed caliper type A fixed caliper type has a pair of pistons to push the disc brake rotor in the both sides. (2) Floating caliper type A floating caliper type is attached the piston only on one side of the caliper. Pistons act the hydraulic pressure. If the disc brake pad is pushed, the caliper slides into the opposite direction of the piston, and pushes the disc brake rotor from the both sides. As a result, it stops the rotation of the wheel. There are several kinds of floating caliper type, depending on the methods to attach the caliper to the torque plate.

7. Types of disc brake rotor

The types of disc brake rotors are

explained below.

• Solid type

There is made from a single disc brake rotor.

•Ventilated type

There is hollow inside. Excellent heat dissipation.

•With drum type

Built- in drum brake for the parking brake.



When the foot brakes are applied (without engine braking)

constantly on a long downhill slope, etc., the lining

and disc brake pads become extremely hot due to friction.

The coefficient of friction of the lining and disc brake pad

surfaces decreases as a result, and the brakes exert less

stopping power even if the brake pedal is depressed with

a great effort.

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