A few models of brake levers have adjustable mechanical advantage. Mechanical advantage may also be adjusted by changing the brake shoe extension or the length of the if a brake uses one, or by replacing the brake, the lever or both. Pulley devices such as the also are available to adjust mechanical advantage.
People with brake problems often think that they need more "power," when they actually need less! In particular, when modern cantilever brakes are used with drop-bar type brake levers, the combination produces excessive mechanical advantage. This problem also arises when using (such as Shimano's "V-Brakes") with levers made for other brakes.
Occasional squeaks are annoying, but they are generally not a safety issue. On the other hand, a loud and persistent squeal makes it hard to modulate the brake. It is usually caused by a new brake shoe that has not worn in, or by grease or oil on the rim.
The typical remedy for this would be to get the vehicle to a stop and wait for a few minutes. As the brake components cool down, their ability to absorb heat returns and the next time the brakes are applied, they seem to work just fine. This type of brake fade was more common in older vehicles. Newer vehicles tend to have less outgassing from the brake pad compounds but they still suffer brake fade. So why? It's still to do with the pads getting too hot. With newer brake pad compounds, the pads transfer heat into the calipers once the rotors are too hot, and the brake fluid starts to boil forming bubbles in it. Because air is compressible (brake fluid isn't) when the brake pedal is pressed, the air bubbles compress instead of the fluid transferring the motion to the brake calipers. Voila. Modern brake fade.