Squealing Disc Brakes

What causes disc brake squeal?

  1. Contamination of braking surfaces
  2. Weak initial break-in period
  3. Glazed pads / rotor
  4. Improper caliper alignment / pad adjustment
  5. Loose braking components / hardware
  6. Resonance / vibration of braking system / fork / frame

How do I fix disc brake squeal?

  1. Clean braking surfaces with isopropyl alcohol
  2. Resurface the brake pads and rotor / follow the manufacturer’s break-in procedure
  3. Adjust the caliper / pads to the manufacturer’s specifications
  4. Check all fasteners for proper torque
  5. Apply SwissStop Disc Brake Silencer

Required Tools / Supplies

  • Clean Shop Towels
  • Nitrile Gloves
  • Isopropyl Alcohol 70%
  • Sandpaper 120 or 220 Grit / Sanding Block
  • T-25 Torx Wrench
  • 5 mm Allen Key
  • Needle Nose Pliers
  • SwissStop Disc Brake Silencer

There are a number of factors that can cause disc brake squeal but the first and foremost culprit is contamination of the braking surfaces from chemicals and oil such as bike cleaners, chain lube or road and asphalt debris will cause disc brake squeal. You will generally feel a loss in braking power if your braking system is saturated with oil; the brake rotor can be degreased easily but the pads should be replaced if they have been compromised as there is not a reliable procedure to completely degrease brake pads.

Second to contamination is a weak initial break-in period of the rotor and pads. As the brake pads and rotors are new, they need to go through an initial break-in period before they start to stop with full power. This procedure deposits an even layer of brake material onto the rotor surface, also referred to bedding-in brake pads. If this layer gets deposited unevenly or the pad cuts through this layer due to an improper break-in interval, the pad will jump when it hits the damaged area and then stick, and this will continue over and over at such a high frequency, eventually leaving you with a “horn” for a brake. Think of a new rotor as a blank metal record which once it is programmed to squeal, it will continue to squeal until you remove the previous braking history from the rotor surface.

Third, pads and rotors can become glazed over if they are overheated prior to performing the initial break-in procedure. This is apparent when the braking surface of the rotor and the surface of the pads look glassy and the rotor arms near the braking surface have changed in color to almost a purple tone. Usually the braking components can be resurfaced and brought back to good working condition but in some cases the pads and rotor must be replaced.

Fourth, improper caliper alignment or pad adjustment can cause excessive braking noise. Brake pads rubbing against the rotor constantly can cause a squeal as well. Check to make sure the caliper and pads are adjusted to the manufacturer’s specifications.

http://www.parktool.com/blog/repair-help/avid-mechanical-disc-adjustment#article-section-1

Finally, some disc brake and frame / fork combinations tend to resonate more than others, regardless of proper setup and break-in procedure. If you have tried cleaning the braking system to remove any contaminants and followed the manufacturer's recommended break-in procedure without success, we have found SwissStop Disc Brake Silencer will help change the resonant frequency of the brake eliminating squeal. Follow the manufacturer's instructions for application available on their website.

http://www.swissstop.com/silencer/

Preliminary Procedure:

Inspect the brake system to ensure it is setup properly according to the manufacturer’s recommendations. Make sure the spokes are properly tensioned, axle nuts are properly secured, hub bearings do not have any play, and all fasteners are properly torqued.

Removing Contamination Procedure:

Apply a small amount of isopropyl alcohol to a clean shop towel and wipe down the braking surface of the rotor; you should see the contaminants transferred to the shop towel. Now move to a clean area of the shop towel and repeat the process until the shop towel looks fairly clean.

Resurfacing Brake Pads / Rotor Procedure:

Remove both wheels from the bicycle and unbolt the rotors using a T-25 Allen key and set aside. Turn the brake pad adjustment knobs counter clockwise until they stop, squeeze the pad tabs together and pull both pads out of the caliper. You may need to use pliers if the pads are difficult to remove. Set the pad spring in a safe place and grab a clean sheet of sandpaper. Place the sandpaper on your workbench and lightly scuff the surface of the brake pads. You are looking to simply rough up the surface while removing a minimum amount of braking material. Now with your rotor laying flat on a clean workbench, take your sanding block with a fresh sheet of sandpaper and sand the braking surface of the rotor in a circular pattern overlapping the edges by an inch or so; continue to sand until almost all of the previous braking history is removed. Once your have resurfaced the rotor and pads, clean them liberally with isopropyl alcohol and reinstall the pads into the caliper. Torque the rotor bolts to the manufacturer’s specification and reinstall the wheels on the bicycle. Adjust the brake pads so that the gap between the inboard pad and rotor is twice the amount of gap at the outboard pad. Finally, perform the break-in procedure described below.

New Pads / Rotor Break-In Procedure:

You can find the manufacturer’s recommended break-in procedure in the Avid service manual and the Magura workshop manual available on the attachments below.

 

Avid Break-In Procedure:

  1. Accelerate the bicycle to a moderate speed, about 15 mph, then firmly apply the brakes until you are at walking speed. Repeat approximately twenty times.
  2. Accelerate the bicycle to a faster speed, about 20 mph, then firmly apply the brakes until you are at walking speed. Repeat approximately ten times.
  3. Allow the brakes to cool prior to any additional riding.
    *Do not lock up the wheels at any point during the bed-in procedure.

Magura Break-In Procedure:

  1. Accelerate the bicycle to about 20 mph.
  2. Brake the bicycle to a stop.
  3. Repeat 30-50 times.

We have found that it is best to bed-in both the front and rear disc brakes simultaneously which will avoid excessive loads on a single brake and minimize unwanted vibrations during the break-in period.

If you have any questions or concerns regarding this technical service bulletin, please contact Pedego tech support at tech@pedego.com or (800) 646-8604 x2.

 

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