Pull a brake pad and notice cracks in the friction material and you might assume the worst. Some pad cracking is normal and harmless; some means the pad is done. Knowing the difference tells you whether to keep driving or replace. Here is the breakdown.
Fine surface cracks (heat checking)
Small, shallow cracks across the friction surface or edges - called heat checking - are common and usually normal, especially on pads that have seen heat. They come from repeated heating and cooling cycles and do not compromise the pad if they stay shallow. Almost any well-used pad shows some fine crazing.
Deep cracks and chunks
The concerning kind are deep cracks that run through the material, cracks that split the pad into pieces, or chunks breaking off. These weaken the pad, can cause noise and uneven braking, and risk a piece breaking loose. Deep cracking often comes from severe overheating, a very old pad, or a cheap poorly-made compound - and can precede delamination.
What causes bad cracking
Extreme heat from riding the brakes or a dragging caliper, age, moisture, and low-quality friction material all drive serious cracking. A pad that overheated once and glazed may also crack - see glazed brake pads. Cheap pads with weak binders crack far sooner than quality ones.
What to do
Fine surface checking on pads with plenty of material left is fine to keep using. Deep cracks, chunks, or pads that are also thin mean replace them now - see when to replace pads. Fit quality pads with fresh hardware and bed them in to avoid the overheating that causes cracking.