Chevrolet Sonic Repair Manual: Brake Assist System Description and Operation
- System Component Description
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The brake assist system consists of the following:
- Brake Pedal
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Receives, multiplies and transfers brake system input force from driver.
- Brake Pedal Pushrod
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Transfers multiplied input force received from the brake pedal to the vacuum brake booster.
- Vacuum Brake Booster
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Uses source vacuum to decrease effort required by driver when applying brake system input force. At rest, source vacuum is applied to both sides of the vacuum diaphragm for single booster. Return springs maintain the booster in a rest position. When brake system input force is applied, vacuum to the rear of the diaphragm is cut off, and air at atmospheric pressure is admitted in its place. This provides a decrease in brake pedal effort required. When input force is removed, vacuum again replaces atmospheric pressure within the booster.
- Vacuum Source
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Supplies force used by vacuum brake booster to decrease brake pedal effort. The source vacuum for a spark ignition engine is normally derived from the intake manifold.
- Vacuum Source Delivery System
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Enables delivery and retention of source vacuum for vacuum brake booster.
- System Operation
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Under normal driving conditions, without the brakes applied, vacuum is allowed to act on both sides of the diaphragm within the vacuum brake booster. When the brake pedal is applied, the effort by the driver is multiplied due to the relative length of the brake pedal in relationship to its pivot point and the point at which the push rod to the vacuum brake booster is attached.
Movement of the push rod causes a valve within the vacuum brake booster to close between the two sides of the diaphragm, thus isolating each side. It also allows a valve to open that allows atmospheric pressure to act on the pedal side of the vacuum brake booster while maintaining vacuum on the vacuum source side of the diaphragm. The movement of the brake pedal pushrod is transferred to the hydraulic brake master cylinder via the vacuum brake booster. The pressure differential within the vacuum brake booster reduces the effort required by the driver in applying the brakes.
General
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Brake Dust Warning
Warning: Avoid taking the following actions when you service wheel
brake parts:
Do not grind brake linings.
Do not sand brake linings.
Do not clean wheel brake parts with a dry brus ...
Other materials:
Sunroof
On vehicles with this feature, the sunroof only operates when the ignition is
turned to ON/RUN or Retained Accessory Power (RAP) is active.
Open/Close: To open the sunroof, press and hold the rear of the switch. To close
the sunroof, press and hold the front of the switch.
Vent: Press and ho ...
Front Seat Belt Anchor Plate Tensioner Replacement
Front Seat Belt Anchor Plate Tensioner Replacement
Callout
Component Name
Warning: Refer to SIR Warning.
Warning: In order to prevent accidental deployment and the
risk of personal injury, do not dispose of a ...
Brake Pad Inspection
Warning: Refer to Brake Dust Warning.
Inspect the disc brake pads at regular intervals, or whenever the tire and
wheel assemblies are removed from the vehicle.
If replacement is necessary, always replace disc brake pads in axle sets.
Inspect both edges of the disc brake ...
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