Document gaZzK9jV7XaVpQLwpXY3DXpQG

LESSON ONE-MODULE 1 BRAKE SYSTEM DIAGNOSIS AND TESTING Brake Noise It is important to realize that some brake noises are normal (for example: early morning squeal). Other noises and brake roughness are abnormal and are cause for concern (for example: metal to metal grinding). These abnormal noises and brake roughness need to be serviced. Normal Noise During normal operation, brake systems may emit an intermittent squeal or groan noise when the brakes are applied. For example, normal noises typically occur during the first few brake applications in the morning or while braking in reverse; however, they may be heard at any time while braking. These noises are aggravated by condi tions such as cold, heat, moisture, road dust, salt or mud. The following noises do not indicate a need for service: Clicking noise during ABS stops. - Noise from the hydraulic pump motor and valves heard while braking during emergency conditions is normal and indicates proper functioning of the vehicle's ABS. This may occur when stopping: On loose gravel. When the tires are unloaded (such as when driving over rail road tracks). On uneven road surfaces. On wet or snowy surfaces. Morning Squeal. - Does not affect brake performance or safety. - Caused by humidity and low rotor and pad temperatures. - Once the brakes are applied and the rotor and pad warm-up, the noise should go away. - Cannot duplicate the condition after the vehicle is driven to the dealership or after the brakes are warm. Groan when creeping. - Inspect the pads for wear. - Does not affect brake performance or safety if the pads are not worn out. - May occur if vehicle is stopped and driver slowly releases the brake pedal allowing the vehicle to creep. Wire brush noise. - Occurs with light braking during early mileage driving. - Caused by new rotors and linings before the friction surfaces are "broken in." - The noise will go away in approximately 100 stops as the friction surfaces are "broken in." 20 September, 2005 Brake System Diagnosis and Repair