Squealing Disc Brakes? Glazed or Contaminated — How to Tell & Fix Them, by The Cycle Workshop on YouTube. 17 min 51 s.
- Video length
- 17 min 51 s
- Time to do it
- 45 minutes
- Difficulty
- Medium
- Steps
- 8
What you need
Steps
Spin the wheel and listen. A constant squeal or scrape points to contamination or a rubbing rotor. A squeal that appears only when braking hard often means glazed pads.
Inspect the pads with a torch. Contaminated pads look oily, dark and shiny with a wet sheen. Glazed pads look glassy and hard, often with a mirror-like surface.
Check the rotor for oil streaks, fingerprints or a blue heat tint. Wipe it with isopropyl alcohol on a clean cloth and see if the cloth comes away dirty.
For glazed pads, remove them and rub the friction surface on 400 grit wet and dry paper on a flat surface until the shiny layer is gone and the surface looks even and matte.
Clean the rotor with isopropyl alcohol and a fresh cloth. Do not touch the braking surface with bare fingers afterwards.
For contaminated pads, clean with isopropyl alcohol first. If the pad material is soaked with oil, replace the pads instead of trying to save them.
Refit the pads and wheel, then check the rotor runs true and the pads clear the rotor when the lever is released.
Bed the brakes in. Ride at a moderate speed and apply the brake firmly about 10 to 20 times, letting them cool between pulls, until they bite evenly and quietly.
Tips and common mistakes
Never use a blow torch on brake pads. It can damage the pad compound and is a fire risk.
Keep oil, chain lube and greasy fingers away from pads and rotors, as this is the most common cause of repeat squealing.
If the noise returns within a few rides, check for a leaking caliper or fork seal rather than just cleaning again.
Replace pads that are worn past the wear line or have a hardened, glassy surface that sanding cannot fix.
Questions
How do I know if my pads are glazed or contaminated?
Glazed pads look glassy and shiny and often squeal only under hard braking. Contaminated pads look oily or wet and usually squeal constantly. A quick sand tells you: glazing comes off as a fine dust, oil smears.
Can I clean contaminated pads instead of replacing them?
Sometimes. Clean them with isopropyl alcohol and sand lightly. If the pad material is soaked with oil or the noise returns, fit new pads.
Why do my disc brakes keep squealing after cleaning?
Usually oil is getting onto the rotor from a leaking caliper, a greasy chain or handling. Find the source before cleaning again.
This guide was drafted from the video's details and general task knowledge. It has not been checked against the full video. Check the video and relevant product instructions before following a procedure. Report a correction.
