The brake repair main servicing items are the occurrence of brake noise and vibration and the wear of the pad and lining.

Brake Noise

Brake noise can be categorized into three types as described below. These noises are produced when the brake pads and brake rotor are grinding each other.

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Brake squeak

The squeaking noise is produced when a smaller slippage of the pad on the rotor surface occurs with high frequency.

Brake groan

The groaning noise is produced when a bigger slippage of the pad on the rotor surface occurs with a lower frequency.

Creep noise

Creep noise occurs only on a vehicle equipped with an automatic transmission. When the brake pedal is slightly released while parking, the vehicle starts to move slowly. Then, the vibration of the rotor and brake pad occurs and it resonates with the suspension and body, which results in annoying noise.

Brake Noise Generating Mechanism

Brake squeak

It is caused by a phenomenon called stick-slip, which occurs between the rotor and pad. When drawing a line on a blackboard as shown below, sometimes chalk vibrates hard and makes a rattling noise.

The explanation for the stick-slip between the blackboard and the chalk. The phenomenon does not occur every time a line is drawn with chalk on the blackboard. The following conditions are necessary for stick-slip between the blackboard and the chalk.

1. Pushing direction and speed of chalk (Driving direction and speed)
2. Pressing force of chalk to blackboard (Braking force)
3. The contact angle between blackboard and chalk
(Contact condition between pad and rotor)
4. Coefficient of friction between blackboard and chalk (Coefficient of friction between the force of pad and rotor)

Brake groan

Rust, flaw, and dust on sliding surfaces of the rotor and drum cause a rubbing noise called groan, which is similar to the noise caused when metals are rubbed together. The noise occurs when the metal base of the pad is rubbed together with the rotor when the pad is worn out completely.

Creep noise

When the brake pedal is released slightly from a standstill, the braking force is decreased little by little and the wheels (rotors) start to rotate due to creeping or moving downhill (driving force> braking force). At this moment, the brake stick-slip phenomenon occurs between the pad and rotor, and it vibrates the suspension. The vibration makes a small sound, and it is amplified by resonance with the body.

Brake Noise Repair Method

Polishing or even replacement of a disc rotor and replacement of drum or backplate of a drum brake may not be the final solution for the brake noise. Only for a short time after the replacement, the squeak does not occur because of the low coefficient of friction due to partial contact between the pad and the rotor. Don’t replace the components without considering this point, because the squeak may recur as the contact becomes normal in a short time.

Brake Repair Ways on How to Fix Squeaking Brakes

Inspect the area where the brake noise occurs for the condition of the pad, shim, and other component parts.
• Sand the surface of the pad with sandpaper (recommendation: # 400).
• Chamfer the entrance and exit sides in the rotor turning direction.

Enlarge the chamfering area to the area from the pad edge to 1/2 of caliper nail leaving a wear limit of 2 mm.

If the shim is damaged, replace it with a new one. Apply disc brake grease between the pad and shim. An effective method is introduced to repair brake squeak by installing a Rubore-shim that reduces brake squeak by restraining the disc brake vibration.

Brake groan

Clean the disc brake rotor and pad, because wear powder of pad, etc. on the brake rotor can cause abnormal noise. It is also effective to make a slit in the disc pad to prevent wear powder of the pad from adhering to the rotor.

Slit cutting method

Draw a line at an angle of 35 to 40 degrees from the pad’s centerline as shown in the figure on the right and cut a slit with a hacksaw. The depth of the slit should not exceed the wear limit. The width of the slit should be equivalent to a thickness of about three cutting blades together.

Creep noise

Creep noise occurs only on a vehicle equipped with an automatic transmission. When the brake pedal is slightly released while parking, the vehicle starts to move slowly. Then the vibration of the rotor and brake pad resonate with the suspension and body, which results in noise. Explain this and convince the customer that it occurs to all vehicles and there is nothing irregular with its operation.

Brake Judder Outline

If the brake disc rotor is distorted, vibration with a thumping feeling is transmitted from the brake pedal to the sole of the driver’s foot when the brakes are applied. At the same time, the steering wheel, instrument panel, and seat body vibrate up and down. (The frequency is about 10 to 30 Hz.) This is a forced vibration of brake frictional force caused mainly by the fluctuation of the braking force. This causes the brake system (disc or drum) to vibrate, which transmits to the body and steering system through the axle and suspension resulting in amplified vibration.

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