Disc brake: A disc brake is a device that produces braking by clamping the brake discs that rotate with the wheels from both sides with friction pads.

1、 Main components and functions of disc brakes: Disc brakes are mainly composed of brake discs, brake calipers, brake pads, and other components.

1 brake disc

Brake discs are generally made of cast iron due to its high coefficient of friction. The brake disc is installed on the wheel hub and rotates with the wheel.

2 brake calipers

The brake caliper spans over the brake disc and is mainly composed of the brake caliper body, piston, piston sealing ring, and dust cover. Its function is to convert hydraulic pressure into mechanical force.

There are two types of brake calipers for disc brakes: fixed and mobile.

(1) The brake caliper body is usually a cast iron component, which is also the cylinder body of a hydraulic cylinder. There are trapezoidal ring grooves on the cylinder wall to facilitate the installation of piston sealing rings; There is an oil passage on the side with a piston; There is an observation hole at the top to check the wear of the brake pads.

(2) The piston of a piston disc brake is made of steel, aluminum, or non-metallic materials.

(3) The function of the sealing ring is to prevent brake fluid leakage between the cylinder wall and piston, while utilizing the elastic deformation of the sealing ring to automatically compensate for the increased brake clearance caused by brake pad wear.

3 brake pads

Brake pads are made by riveting or bonding non-metallic material liners on metal plates, and are placed on both sides of the brake caliper body.

2、 Fixed caliper disc brake: The brake caliper of the fixed caliper disc brake is fixed on the axle housing and cannot rotate or move along the axis of the brake disc.

There are two pistons inside the brake caliper, located on both sides of the brake disc. There is a brake wheel cylinder filled with brake fluid behind the piston. When the driver presses the brake pedal, the hydraulic pressure of the brake wheel cylinder rises, the piston is slightly pushed out, and the brake pads clamp the brake disc to produce braking.

Floating caliper disc brake

The brake caliper of the floating caliper disc brake is connected to the axle housing through a guide pin, which can move relative to the direction of the brake disc axis

When braking, under the action of hydraulic pressure, the piston in the brake wheel cylinder and the brake pads on it are pushed to the left and pressed onto the brake disc. Therefore, the brake disc gives the piston a reaction force to the right, causing the piston and brake caliper to move to the right along the guide pin axis as a whole, until the outer brake pads of the brake disc are also pressed onto the brake disc. At this point, the brake pads on both sides of the brake disc are pressed against the brake disc, clamping the rotating brake disc to produce braking.

1. Brake clearance: refers to the deformation of the sealing ring.

2. Principle: When braking, the brake fluid is pressed into the hydraulic working cylinder to push the piston to move. The edge of the rubber sealing ring also moves with the piston under friction, resulting in elastic deformation. When the braking force is released, the deformation and elasticity of the sealing ring force the piston to retract, thereby restoring the gap between the brake pad and the brake disc.

Automatic adjustment of brake clearance: When the brake clearance is too large due to wear, after the deformation of the sealing ring has reached the limit value Δ during the braking process, the piston overcomes the friction force of the sealing ring and continues to move until complete braking. But after releasing the braking force, the distance that the sealing ring causes the piston to retract is still Δ, which means maintaining the brake clearance as Δ. The function of the piston sealing ring is to ensure the piston returns to its original position and automatically adjust the brake clearance after the brake is released.

Disassembly:

1. Disc brake disassembly

(1) Loosen the wheel bolts and nuts.

(2) Loosen the fastening bolts of the brake caliper housing to separate the brake from the wheel bearings.

(3) Loosen the bolts of the brake cover, and the brake cover can be removed from the steering knuckle body.

(4) Loosen the brake hose connector.

(5) Remove the upper and lower positioning bolts and manually remove the upper and lower positioning circlips.

(6) Remove the brake caliper housing and remove the brake friction plate from the brake base plate.

(7) Press the brake caliper piston back into the brake caliper housing. Before returning the piston, first extract the brake fluid from the brake fluid reservoir, otherwise it may cause the brake fluid to overflow and damage the surface paint. The brake fluid is toxic and can only be stored in a dedicated container when discharging it.

2. Installation of disc brake

① Install a new friction plate. Install the brake caliper housing and tighten the positioning bolts to the specified torque.

② Install the upper and lower positioning circlips.

③ After installation, firmly press the brake pedal to the bottom several times when parking, in order to correctly return the brake pads.

(1) Check the thickness of the brake pads.

(2) Check the thickness of the brake disc. The thickness of the brake disc is 20mm, and the wear limit value is 17.8mm.

(3) The circular jump on the surface of the brake disc friction plate.