09-10
This section describes the noise phenomena occurred possibly in the brake system operation.
Distinguish between the information given below and the actual problems and then, inspect the
vehicle and take appropriate measures.
Noise symptoms and Causes -
Symptom 1. If depressing the brake pedal when the engine is cold, "screeching" sound always
occurs and, after driving for a while, the sound disappears..
This usually occurs in the morning. When the temperature goes down, the dew condensation
phenomenon sets moisture on the brake disc as the window frost forms. Due to this moisture, the
iron within the brake disc and pad oxidizes, forming undetectable micro-rusts on the disc
surface. When starting the engine under this condition, noise may sound due to the friction of
micro-rusts. When operating the brake several times, the disc temperature goes up and the
micro-rusts come off and the noise goes away. Depending on the driving conditions, noise gets
louder when slightly depressing the brake pedal and oppositely, noise is smaller when deeply
depressing the brake pedal. This is simply a physical phenomenon, called "morning effect" in
professional terms, and does not imply any problems with the brake system.
Symptom 2. Slip or screech after the brake pad replacement.
This usually occurs when the bed-in is not made between the disc and the pad's friction material.
The bed-in is a state that the brake system normally works and gives no noise out, when, after
about 300 km city driving, the contact area of the pad friction material is enlarged and the disk is
in complete contact with the pad's friction material. Therefore, for some time after the brake
disk/pad replacement, the brake system poorly operates or noise (abnormal sound) occurs due
to the partial contact.
Symptom 3. "Groaning" sound occurs in the automatic transmission vehicle when slightly taking
the foot off the brake pedal to slowly start after waiting for the signal, or slightly depressing the
brake pedal.
This is the noise "Creep groan" that occurs when, in both the automatic and manual transmission,
slightly releasing the brake pedal in the neutral gear at downhill roads.
It frequently occurs at the low braking power and low speed, through the following process. When
operating the brake system at low speed and low pressure, adhesion and slip repeatedly take
place between the brake disk and the friction material, and this makes the braking power
inconstant, instantly increasing or decreasing, and gives out the brake noise.
It is also a physical phenomenon and has no relation with the brake performance.BRAKE OPERATION AND NOISE ▶
