Brakes squeal / screech / judder

Warning: braking is vital — if in doubt, don't ride and get it checked. Your brakes squeal, squeak sharply, grind, or you feel vibrations while braking. Severity ranges from totally harmless to a wear warning that needs attention. Most often, squealing while braking comes from accumulated brake dust or slight surface glazing — no immediate danger, fixed with simple cleaning. But a metallic grinding sound can be the wear indicator on certain pads (a small metal tab that rubs the disc to signal it's time to replace them). A constant squeal, even without braking, points to a seized caliper piston that keeps the pad in contact (friction, overheating, rapid wear). And pulsations/vibrations felt in the lever while braking suggest a warped disc. You tell them apart with three criteria: is the noise constant (seized caliper) or only while braking (dust, wear indicator)? Do you feel pulsations in the lever (warped disc)? Has bite dropped (wear) or not (harmless dust)? Urgency threshold: simple dust squealing isn't serious, but a noise accompanied by reduced bite, a brake that heats up or drags, or pulsations, should be addressed without delay — and at the slightest doubt about braking effectiveness, go to a professional. Never ignore a continuous metallic grinding: it can mean the lining is gone and the backing plate is scoring the disc.