Hydraulic System: Description and Operation

Brake Fluid and Brake Fluid Handling
Use extreme care when selecting brake system fluids or seal damage can result.
Do not reuse brake system fluids. Do not mix power steering fluid with brake fluid. Fluid contamination may result in swelling and deterioration of rubber parts. This can lead to reduced brake performance and the eventual loss of braking capability.
Service booster components in a clean work area separate from the brake servicing area. Wash hands before changing work areas. Do not use the same containers for brake and power steering fluids.

Caution: Brake fluid may be irritating to the skin or the eyes, or may cause nausea, vomiting, or diarrhea if swallowed. In case of contact or swallowing take the following actions:
^ Eye contact - rinse thoroughly with water
^ Skin contact - wash with soap and water
^ if swallowed - Contact a physician immediately.

Give two glasses of water and induce vomiting by sticking fingers down the throat.

Notice: Brake fluid will damage electrical connections and painted surfaces. Use shop cloths, suitable containers, and fender covers to prevent brake fluid from contacting these areas. Always re-seal and wipe off brake fluid containers to prevent spills.

Always store brake fluid in a closed, sealed container. Never use previously opened containers of stored brake fluid. Always use new brake fluid from a sealed container. Brake fluid left in open or improperly sealed containers will absorb moisture. Moisture can lower the brake fluid boiling point, causing the following problems:
^ Brake system contamination
^ Corrosion
^ Deterioration of rubber components

Substandard Or Contaminated Brake Fluid
It the brake fluid contains improper fluid, water, or other contaminates, the brake fluid may boil or may deteriorate rubber components in the hydraulic brake system.
Evidence of rubber deterioration occurs in the following areas:
^ Swollen master cylinder piston seals
^ Swelling of the wheel cylinder boots
^ Swelling of caliper boots
^ Swelling of the master cylinder reservoir diaphragm

If rubber deterioration is found, replace all rubber parts, including the hoses, in the brake system. Inspect for brake fluid on the brake linings. Replace the brake linings that are contaminated with brake fluid.
If the brake fluid is contaminated and the master cylinder piston seals are good, check for leaks and excessive heat conditions. If no leaks or excessive heat conditions are found, flush the brake system.

Flushing The Hydraulic Brake System
In order to flush the brake hydraulic system, run new brake fluid through the brake system. Continue until the brake fluid at each bleeder valve comes out clear. Flushing is the only way to clean contaminated fluid out of the system. Flush the brake hydraulic system for the following reasons:
^ New hydraulic brake parts are installed
^ Contamination may be present
^ You do not know the grade of brake fluid in the brake system
^ Mineral oil is present in the brake fluid

Brake Warning System Description and Operation
Brake Warning Indicator
The Instrument Panel Cluster (IPC) illuminates the brake warning indicator when one or more of the following occurs:
^ The Body Control Module (BCM) detects that the park brake is engaged. The IPC receives a class 2 message from the BCM requesting illumination.
^ The Electronic Brake Control Module (EBCM) detects a low brake fluid condition. The IPC receives a class 2 message from the EBCM requesting illumination.
^ The EBCM detects an ABS malfunction which disables dynamic rear proportioning (DRP). The IPC receives a class 2 message from the EBCM requesting illumination.
^ The IPC performs the bulb check at the start of each ignition cycle. The brake warning indicator illuminates for approximately 3 seconds before turning OFF.
^ The IPC detects a loss of class 2 communications with the BCM or with the EBCM.

Hydraulic Brake System Description and Operation
System Component Description
The hydraulic brake system consists of the following:
Hydraulic Brake Master Cylinder Fluid Reservoir: Contains supply of brake fluid for the hydraulic brake system.
Hydraulic Brake Master Cylinder: Converts mechanical input force into hydraulic output pressure. Hydraulic output pressure is distributed from the master cylinder through two hydraulic circuits, supplying diagonally-opposed wheel apply circuits.
Hydraulic Brake Pressure Balance Control System: Regulates brake fluid pressure delivered to hydraulic brake wheel circuits, in order to control the distribution of braking force. Pressure balance control is achieved through Dynamic Rear Proportioning (DRP), which is a function of the ABS modulator. Refer to ABS Description and Operation for specific information on the operation of DRP.
Hydraulic Brake Pipes and Flexible Brake Hoses: Carries brake fluid to and from hydraulic brake system components.
Hydraulic Brake Wheel Apply Components: Converts hydraulic input pressure into mechanical output force.

System Operation
Mechanical force is converted into hydraulic pressure by the master cylinder, regulated to meet braking system demands by the pressure balance control system, and delivered to the hydraulic brake wheel circuits by the pipes and flexible hoses. The wheel apply components then convert the hydraulic pressure back into mechanical force which presses linings against rotating brake system components.

Brake Assist System Description and Operation
System Component Description
The brake assist system consists of the following:
Brake Pedal: Receives, multiplies and transfers brake system input force from driver.
Brake Pedal Pushrod: Transfers multiplied input force received from brake pedal to brake booster.
Vacuum Brake Booster: Uses source vacuum to decrease effort required by driver when applying brake system input force. When brake system input force is applied, air at atmospheric pressure is admitted to the rear of both vacuum diaphragms, providing a decrease in brake pedal effort required. When input force is removed, vacuum replaces atmospheric pressure within the booster.
Vacuum Source: Supplies force used by vacuum brake booster to decrease brake pedal effort.
Vacuum Source Delivery System: Enables delivery and retention of source vacuum for vacuum brake booster.

System Operation
Brake system input force is multiplied by the brake pedal and transferred by the pedal pushrod to the hydraulic brake master cylinder. Effort required to apply the brake system is reduced by the vacuum brake booster.