No Pedal / Sinking Pedal

CAUSES
A brake pedal that sinks all the way to the floor is the result of the master-cylinder not developing any hydraulic pressure. This can be caused by a severe fluid leak which has emptied the master-cylinder, or by complete failure of the seals inside the master-cylinder.
A pedal that slowly sinks to the floor is the result of hydraulic pressure leaking off. This may be from an internal leak in the master-cylinder or an external brake fluid leak.

NOTE:Rear brakes which are extremely out of adjustment in conjunction with air in the hydraulic lines can also produce this symptom. Always verify that the shoes/linings are properly adjusted and the brakes have been bled prior to replacing a master-cylinder.

WHAT TO CHECK FOR
- Verify that the fluid reservoir is full.
- Verify that there are no signs of leakage at the area where the master-cylinder bolts onto the brake booster. If any leakage is indicated, the master-cylinder should be replaced.

NOTE: Minor leakage will often be indicated by "bubbled up" paint on the brake booster just below the master-cylinder. Brake fluid is very corrosive to painted surfaces.

- Inspect the rubber gasket on the inside of the master-cylinder lid. If the gasket is swollen or bloated, the brake fluid is contaminated with oil.
- Siphon or scoop a small amount of brake fluid out of the master-cylinder and place into a styrofoam cup filled 2/3 of the way with water. Brake fluid will mix with the water while oil contaminants will float on the surface and dissolve the styrofoam.

NOTE: If any oil contamination is present ALL brake components containing rubber seals will need to be replaced or overhauled. This includes the master-cylinder, both front calipers, both rear wheel cylinders, and all flexible brake hoses.


- Trace all brake lines from the master-cylinder to the calipers and wheel cylinders. Replace any lines that shows evidence of leakage.
- Remove all wheels and inspect the calipers and wheel cylinders for brake fluid leakage. Replace any component that shows evidence of leakage.
- If no signs of external leakage can be detected, bleed the brakes and verify the shoes/linings and emergency brake are properly adjusted.
- If the pedal still sinks to the floor, replace or rebuild the master-cylinder (Non-Antilock Brake Systems only, For ABS systems see Antilock Brake Systems/Testing and Inspection).