How to fix squeaky bike brakes. Oil residue another reason brakes squeak on both rim and disc brakes can be rim contamination particularly with oil residue. To fix this take the wheels out and inspect the brake blocks for dirt. Move the pad from the caliper and sanding down the outer layer with excellent grained sand paper with caution.
This may occur when spray lubricants have been used on a bicycle with disc brakes and some of it gets on the rotors or pads great care is needed if you do use such products. Common causes of squeaky bicycle breaks include brake pads that need cleaning a dirty bike rim brake surface or brake pads that strike the rim evenly across the surface or with the rear part of the brake first. Use a clean cloth or brush to remove most of the dirt.
Brakes that are toed in are most effective. This is an easy fix with just a rag and some rubbing alcohol. Next use a non oil based degreaser or cleaning product and clean cloth to clean the brake blocks and clean all of the rims on both sides.
Lightly dampen the cloth with the alcohol and wipe the braking surface on the rim or the rotor thoroughly. Brakes that are toed in are most effective. As you have contaminated the brakes there is an aspiration.