Hydraulic System: Description and Operation

Brake Fluid and Brake Fluid Handling

Substandard or Contaminated Brake Fluid

Important:
^ Use only Delco Supreme 110 Brake Fluid, GM P/N 1052535 (Canadian P/N 992667), or equivalent DOT 3 fluid.
^ Do not use power steering or transaxle fluid in the brake system.
^ Do not reuse brake fluid collected during system bleeding.
^ Always store brake fluid in a closed container.
^ Reseal brake fluid containers immediately after use
^ Do not use brake fluid left in an open container or an improperly sealed container because it absorbs moisture or can become contaminated.
^ The following fluids may cause the brake fluid to boil or the rubber components in the hydraulic system to deteriorate:
- Water
- A silicone based fluid
- A petroleum based fluid
- Mineral oil
^ The following conditions provide evidence that the rubber components have deteriorated:
- Swollen primary piston cups
- Swollen piston cups on the drum brake wheel cylinders
- Substandard or contaminated brake diaphragm
- Substandard or contaminated master cylinder cover diaphragm
^ If deterioration of rubber is evident, complete the following procedure:

1. Disassemble ail of the hydraulic parts.
2. Wash all of the parts with alcohol.
3. Dry these parts with non-lubricated compressed air before assembly in order to keep alcohol out of the system.
^ Replace all of the rubber parts in the system, including the hoses.
^ Inspect the brake linings for fluid.
^ If excessive fluid is found on the brake linings, replace the brake linings.
^ If the master cylinder piston seals are satisfactory, inspect for the following conditions:
- Leaking
- Excessive heat
^ If these conditions are not found, flush the hydraulic brake system.

Brake Warning System Description and Operation
The brake warning indicator is located in the instrument cluster. The brake warning indicator illuminates in order to warn the driver of conditions in the brake system which may result in reduced braking capability.
The following conditions will turn on the brake warning indicator:
The ignition switch is in the START position. The brake warning indicator illuminates during engine cranking for a bulb check in order to notify the driver that the brake warning circuit is operating properly.
The brake indicator receives ignition voltage through the IG fuse. When the ignition switch is in the START position, a path to ground is provided to the brake indicator through the ignition switch to G200. With power and ground provided, the indicator illuminates.
^ The park brake is applied or not fully released.
When the parking brake is applied, the switch on the park brake lever closes, sending a ground signal to the Daytime-Running Lamps (DRL) control module. The DRL control module controls the ground for the brake indicator.
^ The brake fluid level is low.
If the brake fluid level drops in the master cylinder reservoir, the brake fluid level switch closes, providing a path to G104 for the brake indicator.

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 2 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. The proportioning valve limits the outlet pressure to the rear brakes after a predetermined master cylinder pressure is reached.
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.