The modern-day mountain bike disc brake, be it mechanically or hydraulically actuated, is a technical wonder. These little stoppers offer great control and seldom fade like in the old days. They are not perfect, however. Your favorite trail is a hostile environment for the disc brake, and it will let you know it with an occasional squeal, scrape or rubbing sound.
So, what do you do when your brakes try to tell you something? You take care of the problem so they’ll shut up. Here is how.
The most likely cause for a consistent, loud noise when the brakes are applied is brake pad contamination. Brake pads are porous and can absorb oils of any kind like a sponge. While a contaminated pad can rarely be resurrected, the problem can easily be avoided.
First, always remove the pads and put them in a safe place prior to beginning any maintenance involving brake fluid.
Second, avoid handling the rotor excessively, as even the natural oils on your hands can cause contamination.
Third, because the rear disc is close to the drivetrain, it’s easy to over-spray lubricants and contaminate the pads or rotor. Use a drip-on-style lube that won’t leave your rotor greased up like a rotisserie chicken. If you do happen to contaminate the rotor, try cleaning it off thoroughly with isopropyl alcohol and a clean rag.
BEND IN THE ROTOR
Bent rotors are the cause of most of the pinging noises you hear when the wheel reaches a certain point in its rotation. While most rotors get bent from hitting something on the trail, the tolerances are so tight between the brake pad surface and the rotor that even out-of-the-package rotors can be out of true enough to cause this symptom. In these situations, the rotors can be salvaged by using a rotor-truing fork, like Morningstar’s T/Rale Tool.
If the rotor surface shows any damage or is severely bent, we would recommend replacing the rotor. Riding with a cracked rotor or one that has been trued too many times is asking for trouble in the form of damage to the brake pads and brake caliper—or to your body.
Sticky caliper piston seals can prevent the piston (the thing that pushes the brake pad toward the rotor) from fully retracting. You end up with a brake pad too close to the rotor. This will cause the pad to not only make noise, but also cause excessive drag on the wheel. Piston seals are not the easiest to replace; we recommend having the work done by a trained mechanic. They will need attention after you have replaced your brake pads a few times.
Brake noise is often a symptom of another problem on the bike. Two of the most likely causes are bolt torque and spoke tension. Because noise is a result of vibration, loose parts are typically the culprit. Check the torque on the caliper and the rotor-mounting bolts, and make sure your wheel is properly tensioned.
Improperly aligned disc brake mounts can be the bane of any rider’s existence. Even the best mechanic can’t align the caliper if the frame is not to spec. Facing of the disc tabs is usually done when the bike is first built. However, if it has never been done, it needs to be. This service will make caliper adjustment much easier. This requires an expensive special tool, and since you will only use it on a new bike, it is best to have a shop perform this service.
Riding with worn-out pads can cause irreversible damage to both the caliper and rotor. It can also create horrible brake noise. Brake pads should be removed and inspected for wear every month. Measure the width of the pads, including the backing plate. Anything less than 3 millimeters means it’s time for new pads.
BRING IN THE BIG GUNS
If the brake system is giving you continual problems, it may be necessary to upgrade to a bigger rotor. While larger rotors will add a little weight to your steed, they will dissipate heat better, increase raw power and will cause less noise. You need to check with your shop to see if your bike will accept a larger-diameter rotor.
BRAKE IN PERIOD
While it is awfully tempting to jump on your new steed and rip your favorite descent, it may cause noise problems for you down the road. Proper pad/rotor break-in is necessary whenever a new rotor or new brake pad is installed. To accomplish this, pedal with the brakes applied at a light but consistent pressure for a few minutes on a flat or gradual downhill grade. Be sure not to start and stop while doing this to ensure the pad material is spread evenly. This technique transfers a small amount of the pad material into the rotor’s microscopic pores.
Image: Scott Markewitz
That sweet stream crossing you just nailed will undoubtedly cause some howling from your otherwise perfectly adjusted brakes. Luckily, this is usually a temporary problem. Once the brake is heated again, the problem usually takes care of itself.
THE MOTORCYCLE SOUND
If it sounds like baseball cards are in your spokes, it is probably not a brake issue. You may be the victim of a cruel joke (that the MBA wrecking crew would never try on anyone). Check your chainstay for a rogue ziptie hanging into your rotor. Be sure to return the favor.