Why Disc Brakes Squeal and How Makers Say to Clean Them

The brake screeches when you pull the lever, or squeaks on its own as the wheel turns. Those are two different problems, so start by working out which one you have.

Step 1: Does it squeal only when braking, or all the time?

If the noise carries on with the lever released, check for rub. Park Tool says pad and rotor rub is "the main symptom of a misaligned caliper."¹ Spin the wheel with the bike lifted and listen. iFixit also lists a misaligned caliper as one cause of squeaking, with the pads touching the rotor when the lever isn't pulled.² The fix is alignment, covered by Park Tool in its alignment guides, and by your manual.

Only when braking? Go to the next step.

Step 2: Is there oil or dirt on the rotor or pads?

This is the most talked-about cause. iFixit says that surface contamination on your brake rotors can cause them to squeak.² Park Tool lists brake fluids, oils and grease as things that can ruin pads, even when you can't see them.³

Where does it come from? Park Tool points to spray-can lubricant drifting onto the brake, and to leaks in a hydraulic system.³ iFixit adds that chain oil can reach the rotor, so take care when oiling.² Hands count too. SRAM says oil from your hands can contaminate the pad and reduce braking performance.⁴ iFixit says not to handle the braking surface after cleaning, for the same reason.²

Park Tool's advice on this is brief: "Always look for the source of the contamination."³ Cleaning without stopping the source only brings the noise back.

Step 3: What do makers say about cleaning?

The pages saved for this site say little about cleaning methods. Here's what they do say:

• When fitting a rotor, Park Tool wipes both sides with a clean rag and isopropyl alcohol.⁵
• Park Tool warns against greasing or oiling rotor bolts. Oils can creep outward from the heat of braking and contaminate the rotor.⁵
• Park Tool lists contamination as one reason to replace pads.³

Beyond that, read your own brake's manual or the maker's support page. That goes for which cleaner to use, and for whether a pad can be cleaned or must be replaced. This site doesn't describe sanding or heating pads, because no maker's manual here backs it.

Step 4: Are the pads and rotor new, or a new mix?

Noise from fresh parts often comes down to the bed-in. iFixit lists failure to bed in brakes as a cause of squeaking.² Read bedding in for how makers define it.

Mixed parts matter too. SRAM links a switch of pad compound, with the old rotor kept, to a louder, less effective brake.⁴ The pad materials page has more.

Step 5: Are the parts worn?

Worn pads or a worn rotor can add noise or lower performance. Check pad wear and rotor wear against your maker's limits.

If the brake still makes noise, or the lever feels different after any of this, have a bike shop look at it. A brake that's noisy and also weak shouldn't be left for later.