Fixing rubbing hydraulic disc brakes generally involves re-centering the caliper or addressing piston issues. Here's how you can approach the problem:
Steps to Fix Rubbing Hydraulic Disc Brakes:
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Identify the Source of the Rubbing: Determine which part of the rotor is rubbing against the brake pads. This will help you focus your efforts.
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Re-centering the Caliper: This is often the first and easiest solution.
- Loosen the caliper mounting bolts (the bolts that attach the brake caliper to the frame or fork) slightly. Make sure they're loose enough to allow the caliper to move, but not so loose that the caliper is wobbly.
- Spin the wheel.
- Gently squeeze and hold the brake lever.
- While holding the brake lever, tighten the caliper mounting bolts. Alternate tightening them a little at a time to ensure even pressure.
- Release the brake lever and spin the wheel to check if the rubbing is gone. If not, repeat the process or move to the next steps.
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Piston Reset/Cleaning: Sometimes, one or both pistons in the caliper may be sticking.
- Remove the wheel.
- Remove the brake pads.
- Carefully push the pistons back into the caliper using a tire lever or a clean, flat tool. Be careful not to damage the pistons. This might require some force. The video referenced suggests using a specific tool inserted into the caliper for this purpose to gently ease the pistons back in.
- Clean the pistons with isopropyl alcohol and a clean cloth or cotton swab. Dirt and grime can cause them to stick.
- Reinstall the brake pads and wheel.
- Pump the brake lever several times to re-engage the pistons.
- Check for rubbing and repeat the caliper centering process (step 2) if necessary.
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Check Rotor Trueness: A bent rotor can cause constant rubbing.
- Visually inspect the rotor for any bends or warps.
- If you find a bend, you can try to carefully straighten it with a rotor truing tool or adjustable wrench. Be gentle, as rotors can be fragile.
- If the rotor is severely bent, it's best to replace it.
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Bleed the Brakes (If Necessary): If the pistons are still sticking or the brake lever feels spongy, there might be air in the hydraulic system. Bleeding the brakes will remove the air and improve performance. This is a more involved process and may require a bleed kit specific to your brake system.
Important Considerations:
- Always use clean tools and avoid contaminating the brake pads or rotor with oil or grease.
- If you're not comfortable performing these tasks yourself, take your bike to a qualified mechanic.
- Worn brake pads can also contribute to rubbing. Replace them if they are thin.
By following these steps, you should be able to eliminate most cases of hydraulic disc brake rubbing.
