As the most common mode of transportation in our daily lives, electric bikes are undergoing increasingly rapid upgrades, with their components becoming more advanced! Nowadays, since disc brakes are used a lot on bikes, there are more and more problems and malfunctions while riding. Let's figure out together how to fix common disc brake problems and learn some practical ways to deal with them.  

What is a disc brake?

A disc brake, also called a pad brake, is made up of a brake disc that's hooked up to the wheel and a brake caliper that's put on the edge of the brake disc. How it works is, high - pressure brake fluid pushes the brake pads to squeeze the brake disc, and that's how the braking force gets created.  

Disc Brake Structure 

Disc brakes, also known as disc-type brakes, operate by a hydraulic pump driving the brake caliper to clamp the brake disc. To enhance braking force, based on the formula F=P*S, methods typically include increasing the braking surface area to expand the contact surface; extending the braking lever arm; Additionally, pressure amplification via the hydraulic pump can increase force intensity. Furthermore, enlarging the brake disc diameter boosts braking torque to enhance overall braking force.

Advantages and Disadvantages of Disc Brakes

Advantages: External design, excellent heat dissipation, linear braking, easy control, and suitable for frequent light braking.

Disadvantages: Relatively lower braking force compared to rim brakes, and higher cost.

Many brake rotors on the market now feature drilled designs, which serve to enhance heat dissipation and optimize thermal fade performance.

Common Disc Brake Failures

1. Brake Issues Caused by Upper Pump Quality

As industry price wars intensify, some manufacturers cut costs by using plastic pistons in upper pumps and employing substandard oil seals. Pumps of this quality quickly develop oil leaks from the seals or lose pressure. Replacing the upper pump typically resolves the issue.

2. Impact of Brake Fluid Quality on Disc Brakes

If disc brakes lose pressure shortly after servicing and require bleeding to restore normal function, only to exhibit the same issue overnight, the brake fluid is likely the culprit. Inferior brake fluid absorbs moisture from the air during braking, causing chemical reactions that generate significant gas buildup—the primary cause of lost pressure.

3. Rear Wheel Lockup

To address this, open the lower master cylinder to bleed air and observe fluid flow. If fluid sprays out upon opening while the rear wheel feels lighter, it indicates a pressure issue likely originating from the upper master cylinder or brake lines. If fluid slowly drips out with the rear wheel remaining heavy, it points to a mechanical problem with the lower master cylinder.

4. Brake Fluid Line Impact

The brake fluid pipes can expand and contract as the temperature changes. At noon when it's really hot, the pipes expand. This makes the brake fluid flow from the storage tank to the upper storage tank, and that causes the pressure to go down. When doing maintenance, just add some brake fluid and it can go back to working properly.

But at night, when the temperature drops, the pipes shrink. This will push the brake fluid back into the storage tank. It might make the level in the storage tank too high, and then the rear wheels could lock up.   This is what mechanics often describe as “working fine during the day but locking up at night,” or “working fine at night but having no brakes during the day.”

Maintenance of Disc Brakes

1. Check if there's any brake fluid leak. If you find a leak, wipe up the spilled fluid and head to a repair shop right away to figure out and fix what's wrong.

2. Check the brake calipers for dirt or bits of debris. Clean them thoroughly. Contaminants can make the brake cylinder and the friction pads get out of alignment. That'll make the braking performance worse and make the system wear out faster.

3. Replace the brake fluid on a regular basis.

4. Set up regular visits to the repair shop. Make sure the brake fluid level isn't lower than the lowest mark. Also, have a look at how much the friction pads and brake discs are worn.