GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1998 🢒 Grand Am 🢒 Brakes 🢒 Hydraulic Brakes 🢒 Master Cylinder Diagnosis

The following inspections determine all master cylinder malfunctions. If the problem is not found by using the following tests, refer to Brake System Diagnosis Brake System Diagnosis in order to help isolate the problem.

    • Eye contact--rinse thoroughly with water.
    • Skin contact--wash with soap and water.
    • If ingested--consult a physician immediately.

Important: 

   • Use only Delco Supreme II Brake Fluid GM P/N  12377967, or equivalent DOT-3 brake fluid.
   • Do not use power steering or transmission fluid in the brake system.
   • Do not reuse brake fluid accumulated during the brake system bleeding.
   • Always store brake fluid in a closed container. Reseal brake fluid containers immediately after use.
        Do not use brake fluid that was left in an open or improperly sealed container. The brake fluid will absorb moisture or may become contaminated.

  1. Inspect for a cracked master cylinder casting.
  2. Inspect for brake fluid around the master cylinder. A leak is present if there is at least one drop of fluid. A damp condition is not abnormal.
  3. Inspect for a binding pedal linkage.
  4. If the pedal linkage is correct, disassemble the master cylinder. Refer to Master Cylinder Replacement . Inspect for swollen or elongated primary piston seal(s).
  5. If the seals are swollen, substandard or contaminated brake fluid is the probable cause. If the brake fluid is contaminated, use the following procedure:
    6. 5.1. Disassemble and clean the serviceable components.
    5.2. Replace all of the rubber and non-serviceable components.
    5.3. Flush all of the brake pipes and brake hoses. Refer to Hydraulic Brake System Flushing

Any of the following conditions may cause the brake fluid to boil:

    • Improper brake fluid
        Improper brake fluid may also cause the rubber components to deteriorate.
    • Power steering fluid
    • Transmission fluid
    • Water in the brake fluid

If the master cylinder cap diaphragm is swollen, then rubber parts have deteriorated. Deterioration may be evident by swollen wheel cylinder boots and caliper boots.

If deterioration of the rubber parts is evident, complete the following steps:

  1. Disassemble all serviceable hydraulic components.
  2. Wash the components with alcohol.
  3. Dry the parts with non-lubricated compressed air before assembly in order to keep alcohol out of the system.
  4. Replace all rubber parts in the system, including hoses and non-serviceable hydraulic components.
  5. Refill the master cylinder reservoir with new brake fluid.
  6. Flush the brake system. Refer to Hydraulic Brake System Flushing
  7. Bleed the brake system. Refer to Hydraulic Brake System Bleeding