2021 BMW M850i xDrive Brake Master Cylinder Replacement Cost

The term 'spongy' is well known in the automotive field, and describes the feeling of the brake pedal when air has been introduced into the master cylinder, or the master cylinder has pushed air into the brake lines. The brake pedal may also sink to the floor when pressed and held. This indicates the plungers inside the master cylinder are leaking internally, and will not produce the pressure needed to cause the vehicle to slow or stop. Learn more about brake master cylinder symptoms

It is not safe to operate any vehicle with any braking problem. If there exists any sign that the brakes are not performing as originally intended, the vehicle should immediately be placed out of service, and repaired. Collisions result from brake system failure, and the parking brake should never be substituted for the normal service brakes.

Replacement of the brake master cylinder is a common repair to many makes and models, however, the majority of vehicle's will not need this repair before 125,000 miles. This is because there are very few moving parts, and the system is sealed from air, dust, and other brake fluid contaminants. Each manufacturer protects their customers from master cylinder failure by providing a schedule for maintenance for the entire braking system. This maintenance includes flushing the brake fluid, cleaning, and inspecting components, as well as replacement of wear and tear parts. Following these recommendations may even ensure the master cylinder will last the lifetime of the vehicle. However, neglecting maintenance specified by the factory may cause premature wear of the master cylinder plungers, leading to an early onset of the mentioned symptoms.

The operation of the brake pedal is the best indicator of master cylinder failure. If the pedal falls to the floor when pressed, little or no braking force is being created, and there are no external leaks, there is a strong possibility the master cylinder has failed. If the brake pedal becomes firm after pressing quickly and repeatedly, but returns to the floor when held, the master cylinder will most likely be at fault.

After the brake fluid is drained from the system, the brake lines must be removed from the master cylinder. There is normally one electrical connector to remove, and finally, the master cylinder can be unbolted and removed from the brake booster. Replacing the master cylinder is the reverse order, but the master cylinder must be bled of air prior to bleeding the air from the rest of the braking system.