Hearing a squealing sound coming from a wheel while driving is the most common way to tell brake pads need to be replaced. Brake pads are equipped with a wear indicator that creates a squeal when they are too thin.
A soft or spongy feel while applying the brake pedal is another indicator of worn brake pads. Worn pads require the brake piston to travel farther, therefore displacing more hydraulic fluid from the master cylinder. Visual inspection is another way to determine if pads need replacing. If the pads are not visible through the spokes of a wheel, it is necessary to remove the wheel for visual inspection. Brake pads need replacing if they are less than one-quarter of an inch thick.