Repair guides › Brakes
Fix squealing disc brakes
A caliper on the fork and frame that squeezes pads against a steel rotor when you pull the cable. Most budget mechanical calipers (Logan, Tektro, Promax and similar) are single-sided: the cable turns an arm that pushes the outer pad, which flexes the rotor slightly onto the fixed inner pad. The inner pad has a dial or bolt to move it closer as pads wear. The caliper position on its mounting bolts sets the alignment.
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Tools
- Ball-end hex key set (1.5–10 mm): Park Tool HXS-1.2 Professional L-Shaped Hex Set ($$)
- 1/4" click torque wrench (about 2–17 Nm) + bits: Pro Bike Tool 1/4 inch drive click torque wrench set (2.2–16.9 Nm) ($$)
- Shop rags + nitrile gloves: shop towels and nitrile gloves ($)
- Isopropyl alcohol 91%+: isopropyl alcohol 91% ($)
- Disc brake cleaner spray: Finish Line Bicycle Disc Brake Cleaner, 10 oz ($)
Compare Good, Better and Best for each tool
Steps
- Check the caliper and rotor bolts are tight. Loose hardware vibrates and sings.
- Clean the rotor with isopropyl alcohol.
- Remove the pads. If they look glazed (shiny), sand them lightly on flat sandpaper.
- If they are oily or dark-stained, replace them. Contaminated pads do not recover.
- Re-bed the pads.
- Still squealing? Organic (resin) pads are quieter than sintered metal pads. Some rotors are stamped "Resin pad only": never fit sintered pads to them. If you switch pad type, clean the rotor and bed in again. (SRAM says to fit a new rotor when you change pad compound.)
Signs it needs doing
- Rub or tick each wheel revolution (rotor bent or caliper misaligned)
- Lever pulls to the bar (pads worn or cable stretched)
- Squeal (contaminated pads or loose caliper)
- Grinding metal (pads worn to the backing plate: stop now)