In the world of high-performance driving, there’s nothing more unsettling than a mushy brake pedal. Oftentimes this is the direct result of shortcuts taken when installing a new master cylinder. The most universal cause of a spongy brake pedal is air in the system. Brakes are applied using hydraulic pressure created at the master cylinder. If even a small amount of air is trapped anywhere in the system, this creates that unsteady pedal.
One of the most common causes of air in the system when replacing or repairing a master cylinder is skipping the process of bench bleeding the master. To be blunt, that shortcut just doesn’t work. Air is nearly guaranteed to be trapped inside the master cylinder when the bench procedure is ignored. This happens because master cylinders are often mounted in the vehicle
