There can be many problems and solutions when it comes to bicycle brakes. This article will attempt to cover all the common problems in caliper-type brake systems and only briefly mentions the torpedo brake.
Steps
Method 1 of 6: Checking the calipers

Step 1. Check the brake pads
The first thing you need to know is if your brake pads are too worn to work properly. There must be at least 8 mm of rubber (the brake pad) between the caliper and the tire when the caliper is actuated. If the inserts are worn out, you will have to replace them.

Step 2. Check cables
Depress the brake actuators and make sure the cables move. Otherwise, the cable may be stuck or the hitch may be loose.

Step 3. See if the calipers move when the brake is pressed
If the brake cable moves close to the brake lever but does not move close to the caliper, the cable could be torn inside its plastic cover. So it will have to be replaced completely.

Step 4. Look at the caliper to see that both sides hold the tire at the same time
If only one side moves, you can see that only one pad is being actuated, and this will not allow for efficient braking. You may need to loosen the clamp screws to try to unlock the side that is stuck. A good lubricant can do the trick.
Method 2 of 6: Changing Brake Pads

Step 1. Buy new brake pads
If you know the make and model of your bike, you will probably have no problem finding compatible pads at a specialist store.

Step 2. Remove nuts and washers and release inserts from caliper
On most bicycles, this can be done without having to remove the clamps from the bicycle frame.

Step 3. Install the new pads, taking care to keep the surfaces in line with the tyre
Make sure the insert height is close to the wheel rim. If it gets too low, the insert can slip out of the rim, causing a dangerous situation, and if it gets too high, it can scrape the tire, which isn't good either.
Method 3 of 6: Maintaining Cables

Step 1. Lubricate the collet shaft

Step 2. Check the adjustment of your brake cables
When the brakes are not applied, the pads should be about 8 mm from the tire rim, and when the brake lever is applied, they should fully contact the rim halfway through the lever.

Step 3. Lubricate the cables
You can spray an aerosol lubricant where the cable enters its plastic cover, near the brake lever. Various types of oil can be purchased at auto parts stores.

Step 4. Remove the cable from its plastic cover, only if it is too rigid, or difficult to operate
This is done by removing the hitch on the caliper or brake lever, and pulling the cable in the opposite direction. If you do remove the cable, use an aerosol lubricant (or even WD-40) to remove dirt and debris from the cable. Apply a light coat of lithium grease or machine oil to the cable and reinstall if undamaged.

Step 5. Thread the loose end of the cable through the hitch at the end you removed earlier and check how far the brake lever can be pressed before the brake touches the tire
When the brake pads are about 6 mm from the tire with the brake lever released, tighten the hitch.

Step 6. Replace only the cable, or the entire cable assembly if the above steps do not solve the problem of the cable not moving when applying the brake
Buy a cable the same diameter, brand, and length as the original. Aligning, cutting to the same size and passing through the couplings are a bit tricky tasks.
Method 4 of 6: Servicing the Brake Levers

Step 1. Check the cable hooks on the underside of the brake levers to make sure they are secure

Step 2. Lubricate the axle bolts on the lever
Method 5 of 6: Maintaining the calipers

Step 1. Make sure the calipers are level above the tire

Step 2. Check that the springs are tensioned evenly on each collet arm
If one side moves more than the other when the brake lever is pulled, you must make sure both arms are moving freely and well lubricated. Squeeze the spring of the moving arm further by bending with pliers, being careful not to cut or break the spring.
Method 6 of 6: Torpedo brake

Step 1. Rotate your bike's pedal backwards if your bike is equipped with a torpedo brake
The pedals should only go back ¼ of a turn and the brake should be applied. This all happens inside the rear axle, and maintenance is not recommended for beginners.

Step 2. Check the brake arm
It is usually a flat iron arm fitted to the rear axle opposite the belt, which is attached to the lower frame. See if the hitch is loose, allowing the arm to rotate with the axle. If it is loose, reattach the forward-facing arm of the bike.
Tips
- Don't buy a smaller brake pad.
- If you don't know how to assemble or disassemble the brake mechanism, don't try. Ask someone who knows for help.
- An incorrectly mounted mechanism can leave the brakes constantly scraping the tire!
- Always read the user manual.
- If nothing goes well, take it to a store and pay for a job well done.
Notices
- Securely fasten the new inserts so that they work efficiently.
- Walk slowly to test the brakes before accelerating!!!