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:
Loss of Control
Skidding
There are three types of skids that correspond to the vehicle's three control
systems:
Braking Skid — wheels are not rolling.
Steering or Cornering Skid — too much speed or steering in a curve causes
tires to slip and lose cornering force.
Acceleration Skid — too muc ...
Piston and Connecting Rod Assemble
Special Tools
EN-49941 Remover / Installer Piston Retainer Ring
For equivalent regional tools, refer to Special Tools.
Note: Lubricate the piston pin with clean engine oil.
Install the connecting rod (3) and the piston pin (2) to the piston (1).
Install t ...
Bushing and Mating Shaft Inspection
Note: Proper bushing and corresponding mating shaft inspection should
be performed before replacing the bushing, shaft, and in some cases, the component
which houses the bushing. Thoroughly clean and dry the bushing and shaft surfaces
before inspecting for damage.
Any of the followin ...
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