Most low brake pedal problems are caused by air in the hydraulic system. Bleed the system until all air is purged. Refer to Bleeding Brake Hydraulic System in this section. Other less frequent causes of excessive pedal travel are excessively worn linings and hydraulic system leakage. At reasonably frequent intervals, the brakes should be measured for pedal travel, which is the distance the pedal moves toward the floor from a fully released position.