Auto Repair Encyclopedia
Brake Master Cylinder Replacement
Sometimes referred to as Brake Master Cylinder, Master Brake Cylinder, Master Cylinder Brake, Master Cylinder
The brake master cylinder generates hydraulic pressure necessary to slow down or stop a vehicle. The master cylinder is located in the engine compartment.
When the brake pedal is applied, the brake master cylinder generates hydraulic pressure, which is then distributed to each wheel. This pressure then engages either the brake pads or brake shoes to slow down or stop the vehicle.
To replace the brake master cylinder, brake fluid is removed from the brake fluid reservoir. Then the brake lines are removed from the master cylinder. After the new brake master cylinder is installed, brake fluid is added to the reservoir. A brake bleeder screw is opened at each wheel, and the brake pedal is continually depressed until fresh brake fluid exits at all wheels.
Brake fluid naturally absorbs moisture from the surrounding air. Moisture is the enemy of any hydraulic system; it lowers the operating efficiency of the brake system, and it may result in costly repairs if the brake fluid is not periodically replaced. The brake system is sealed and should not require frequent topping up. If the brake fluid does require frequent topping up, the brake system has a leak that must be investigated.
About this Repair: Brake Master Cylinder Replacement
Recommendations
Problems elsewhere in the brake system can cause symptoms similar to a defective brake master cylinder, including stuck calipers and ABS valve bodies. Have the shop inspect the entire brake system to verify that the problem is specific to the master cylinder.
Flushing brake fluid at least every two years can extend the life of brake master cylinders.
Why this happens
A failing brake master cylinder can cause a "spongy" or "sinking" brake pedal that is not very responsive while braking and stopping. A common complaint is that the "brake pedal goes to the floor when braking". This is a very dangerous condition and the vehicle should not be driven in this condition.
A defective brake master cylinder can set a diagnostic trouble code and cause a warning light on the dashboard to illuminate.
Brake master cylinders are often replaced because they have begun to leak brake fluid.
