Brake pads consist of friction material bonded to a metal backing plate, which presses against the rotors to slow a vehicle. This friction naturally causes the material to wear down over time. Visual inspection is necessary to determine if the pad is still capable of performing its function. This analysis focuses on the visual evidence of a bad brake pad, allowing an owner to assess the current condition of their braking system by sight alone.
Minimum Thickness Indicators
The most direct visual sign of a bad brake pad is insufficient friction material remaining. New brake pads typically measure 10 to 15 millimeters in thickness. Automotive specialists suggest replacement should be scheduled when the pad material wears down to a thickness of 3 to 4 millimeters.
This 3-to-4-millimeter threshold is accepted because less material diminishes heat dissipation capabilities. Reduced heat absorption can lead to overheating and a reduction in stopping power. The minimum safe thickness for a brake pad is generally considered to be 3 millimeters, which is roughly the thickness of a few stacked pennies.
To check the thickness, observe the material through the wheel spokes or the caliper opening, focusing on the dark friction material against the metal backing plate. Many pads include a built-in mechanical wear indicator—a small metal tab attached to the backing plate. When the pad material wears down to the minimum limit, this tab is designed to make contact with the rotor.
The metal tab scraping against the rotor creates a high-pitched squealing sound, offering an auditory alert that the pad has reached its minimum thickness. Visually, the pad material will appear extremely thin, positioned close to the rotor’s surface. At this stage, the pad must be replaced immediately to prevent damage to other components.
Surface Deterioration and Damage
A brake pad may be compromised even with adequate thickness, typically due to excessive heat or mechanical issues. One common sign is glazing, which occurs when the friction material overheats and the surface resins harden. This process transforms the pad surface into a smooth, dark, and shiny, glass-like finish.
This glassy appearance indicates the material has lost its ability to generate proper friction against the rotor, compromising stopping performance. Glazing can be accompanied by visible cracks or chips in the friction material, signaling structural integrity failure from extreme thermal stress.
Another visual indicator is uneven wear, such as tapered wear, where the pad material is significantly thinner on one side. This uneven consumption suggests a mechanical fault, such as a stuck caliper or worn guide pins, causing the pad to press against the rotor at an angle.
Observing glazing, cracking, or severe tapering means the pad is bad, regardless of its remaining thickness. These visual cues point to underlying issues in the braking system that prevent the pad from functioning correctly.
When the Backing Plate is Exposed
The most severe visual sign of a bad brake pad is the complete absence of friction material, exposing the metal backing plate. This represents the final stage of pad wear, where the steel plate grinds directly against the rotor face. Only the silver or gray metal of the plate is visible where the dark pad material should be.
The metal-on-metal contact creates a distinct visual effect on the brake rotor itself. Deep grooves, scores, or gouges will be visibly etched into the rotor’s surface, often appearing as concentric circles. This severe scoring is caused by the hardened steel of the backing plate tearing into the softer cast iron of the rotor.
The exposed backing plate and resulting rotor damage indicate a catastrophic failure. The braking system is severely compromised, requiring new brake pads and the replacement or machining of the damaged rotors. Continued driving will only deepen the rotor damage and increase stopping distances.