Bikes are mechanical devices and can make assorted noises and annoying sounds. One common and disturbing occurrence you might come across is squealing when you press the brake levers. The brakes probably work fine, they just get noisy. Understanding how brakes function, the individual parts and what can cause them to squeak will help you make adjustments. A little tweaking is all your brakes need to stop the squeal.
Brakes vary by design and manufacturer, but the basics are similar whether you have cantilever, rim or rod brakes. The job of the brakes is to slow the movement of the wheels. To do this, they use pads that touch the surface and cause friction. The difference in brake systems generally is in the lever action or individual components. Regardless of what causes the action, you still need something to touch the rim surface and slow movement. This is why any braking system can eventually develop a squeal.
The brake pad is the part that touches the rim to stop the bike. Most pads have a rubber construction kept in place by a metal shoe. The number of pads may vary by brake design. When the rubber pad touches the rim, it causes friction to slow down rotation. Brake pads are the source of your squeal. The sound you hear is the pad touching the rim surface.
Squealing does not usually affect the function of the brake, but it can be a sign that something is off kilter. Healthy brakes should not squeal. One likely cause of the noise is age. Old pads wear down and squealing is a sign you should replace them. The first step, when brakes start squeaking, is to check the pads. Secure the bike on a solid surface and look toward the rear wheel. You should see a U-shaped component that wraps over the top of the tire. Examine the rubber ends. These are the pads. If the pads appear worn or flattened on one side, replace them.
Toed-in is a term that describes how brake pads should touch the rim. When you press the brake lever, the pads touch at the front first. The front of the pad is nearest the bike seat. Pads that are not toed-in will squeak. If the pads hit the surface flat, as opposed to toed-in, adjust them. The adjustment will depend on the brake system. In most cases, you turn a screw or nut to loosen the brake shoe, tap on the front of the shoe to alter the angle and retighten. Test ride the bike. If the stop is too abrupt, the angle is too tight, because the front pad is too close to the rim. Loosen the brake shoe again and move the front of the pad back a bit. It may take some trial and error to get the toed-in position correct. Once the angle is correct, the squealing should stop.