Hard and Soft Brake Pedal Diagnosis

A faulty brake booster causes a hard brake pedal and a faulty master a soft pedal.

A soft and spongy or a rock hard brake pedal with little stopping power is a sure sign something is wrong with the brake system; but what? Where to begin? When the pedal's soft, air may have entered the system, or there could be a problem with the internal seals in the master cylinder. A hard brake pedal typically points to the brake assist unit.

Soft Brake Pedal

Leaking master cylinder cup seals.

Leaking master cylinder internal cup seals result in a fading brake pedal. It's important to inspect the brake system and rule out other possible causes. Loose or faulty wheel bearings will result in a low spongy brake pedal. Inspect each brake unit for leaks or swollen hoses. Make sure there’s no air in the system.

Hard Brake Pedal

Vacuum assist brake booster.

Brake booster failure causes a hard brake pedal. Hydroboost systems rely on pressure from the power steering system. Vacuum assist units require sufficient vacuum to operate correctly. Sometimes this vacuum is blocked at the intake manifold port. A kink in the check valve hose will also result in this hard brake pedal condition. Cleaning this port or repairing the check valve's hose will restore vacuum and brake booster operation. If the brake pedal’s hard, suspect the brake booster. If the pedal fades to the floor, suspect the master cylinder.