How can I tell how worn the brake linings are?

Thickness observation: For brake linings on disc brakes, the thickness of the brake lining can be viewed directly through the rim gap. Typically, the brake lining will have wear marks on it, and when the remaining thickness is close to or less than that indicated by the wear marks (usually around 2 - 3 mm), replacement will need to be considered. For drum brakes, it may be necessary to dismantle the wheel and drum to see the thickness of the brake lining on the brake shoes.

Surface Condition View: Check the surface of the brake lining for uneven wear, cracks, flaking, etc. If there are obvious scratches on the surface of the brake lining, it may be caused by uneven surface of the brake disc or drum; if there are cracks or flaking, it will seriously affect the braking performance and need to be replaced immediately.

Braking noise judgement: in the braking process, if you hear a sharp metal friction sound (similar to the 'squeak' sound), it is likely to be the brake lining has been excessive wear, the metal backing plate and the brake disc or drum began to contact the sound. However, some high-performance brake linings may also produce a slight noise during normal operation, which needs to be judged in conjunction with other inspection methods. In addition, if you hear a 'rattling' sound, the brake lining may be loose or a foreign object may have entered the braking system.

Longer braking distance: If the braking distance is obviously longer than before when the vehicle is braked at normal travelling speed, it may be caused by insufficient friction due to the wear of brake linings, and the condition of the brake linings needs to be checked at this time.
Changes in brake pedal feel: When brake linings are worn, the feel of the brake pedal will also change. There may be a longer pedal stroke because the thinning of the brake lining requires the piston to move a greater distance in order for the lining to make contact with the disc or drum. In addition, the pedal may become soft to the touch, due to the hydraulic pressure in the braking system not being effectively converted into friction through the worn brake linings.

Most modern vehicles are equipped with brake system warning devices. When the brake linings are worn to a certain level, a brake system-related warning light will illuminate on the vehicle's dashboard. This warning light may be a specialised brake lining wear warning light, or it may be a generic warning light associated with a brake system malfunction. For example, some vehicles monitor the thickness of the brake lining via wheel speed sensors and signal the driver when the thickness is insufficient.