Hydraulic System: Description and Operation

Brake Fluid and Brake Fluid Handling

Caution: Brake fluid may be irritating to the skin or eyes. In case of contact, take the following actions:
^ Eye contact Rinse eyes thoroughly with water.
^ Skin contact-wash skin with soap and water.

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.

Use Delco Supreme 11(R) Brake Fluid GM P/N 12377967, or an equivalent DOT-3 motor vehicle brake fluid. 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

Notice: Power steering fluid and brake fluid cannot be mixed. If brake seals contact power steering fluid or steering seals contact brake fluid, seal damage will result.

Use the correct fluids on models with a hydraulic booster. The master cylinder and brake system use brake fluid. The hydraulic booster system uses power steering fluid. If 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. Check 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
Flushing the brake hydraulic system is running new brake fluid through the brake system until the brake fluid at each bleeder valve comes out clear.
Flush the brake hydraulic system for the following reasons:
^ When new hydraulic brake parts are installed.
^ When contamination may be present. Flushing is the only way to clean contaminated fluid out of the system.
^ When you do not know the grade of brake fluid in the brake system.
^ When mineral oil is present in the brake fluid.

Brake Warning System Description and Operation (DRL Equipped)
Brake Warning Indicator
The Brake Warning Indicator illuminates when the when one or more of the following occurs:
^ The EBCM performs the bulb check. The EBCM applies ground to the ABS pressure differential sensor signal circuit.
^ The brake pressure differential switch is closed by a pressure differential between the front and rear brake circuits. The brake pressure differential switch applies ground to the ABS pressure differential sensor signal circuit. In turn, the DRL Control Module applies ground to the brake warning indicator control circuit.
^ The park brake is engaged. The park brake warning switch applies ground to the park brake switch signal circuit. In turn, the Daytime Running Lamps (DRL) Control Module applies ground to the brake warning indicator control circuit.
^ The ignition is turned to START. The ignition switch applies ground to the park brake switch signal circuit. In turn, the DRL Control Module applies ground to the brake warning indicator control circuit.

Brake Warning System Description and Operation (Without DRLs)
Brake Warning Indicator
The Brake Warning Indicator illuminates when the when one or more of the following occurs:
^ The EBCM performs the bulb check. The EBCM applies ground to the ABS pressure differential sensor signal circuit.
^ The brake pressure differential switch is closed by a pressure differential between the front and rear brake circuits. The brake pressure differential switch applies ground to the ABS pressure differential sensor signal circuit.
^ The park brake is engaged. The park brake warning switch applies ground to the brake warning indicator control circuit.

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 a combination valve.
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.
Hydraulic Brake Booster: Uses power steering fluid pressure to decrease effort required by driver when applying brake system input force. When brake system input force is applied, pressurized power steering fluid is admitted to the rear of an apply piston, providing a decrease in brake pedal effort required. When input force is removed, pressurized power steering fluid is blocked off from the piston.
Power Steering System: Supplies pressurized power steering fluid used by hydraulic brake booster to decrease brake pedal effort.

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 hydraulic brake booster.