GM Service Manual Online
For 1990-2009 cars only

Use extreme care when selecting brake system fluids or seal damage can result. Refer to Fluid and Lubricant Recommendations in Maintenance and Lubrication in order to select the correct fluid.

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 may result in 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

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. 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, inspect 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