Performing a brake bleed with a MityVac is the most efficient and reliable method for DIY enthusiasts and professional technicians alike. This process uses vacuum pressure to pull old, contaminated fluid through the system and replace it with fresh fluid, ensuring a consistent and bubble-free result. Unlike the traditional two-person method, a MityVac allows a single person to complete the job accurately, reducing the risk of introducing air back into the lines.
Understanding the Basics of Brake Bleeding
Brake fluid is hygroscopic, meaning it absorbs moisture over time, which lowers its boiling point and creates a spongy feeling in the pedal. Air is compressible, and any presence within the hydraulic lines compromises the system's ability to transfer force from the pedal to the calipers. The goal of bleeding is to purge this air and restore a solid, responsive pedal. A MityVac simplifies this by applying negative pressure at the bleeder valve, which forces fluid and air out the top without requiring manual pumping or a second person to catch the fluid.
Gathering Tools and Safety Equipment
Preparation is key to a successful bleed, and having the right tools ensures a clean and safe procedure. You will need a quality MityVac vacuum pump kit, the correct type of brake fluid for your vehicle, a set of wrenches that match your bleeder screws, clear vinyl tubing, a catch bottle, and a container for used fluid. Safety is paramount, so wear gloves to protect your skin from the harsh chemicals and safety glasses to prevent fluid from splashing into your eyes. Additionally, ensure the vehicle is securely lifted and the tires are chocked if you are working on it while it is elevated.
Preparing the Vehicle and Vacuum Pump
Before attaching the vacuum, you must prepare the master cylinder reservoir. Open the reservoir caps and top them off with fresh brake fluid; this prevents the reservoir from running dry during the process, which would pull air into the system and ruin the bleed. Connect the appropriate size adapter from the MityVac kit to the bleeder valve, and attach the clear vinyl tubing to the other end of the adapter. Submerge the opposite end of the tubing into a jar filled with fresh brake fluid to prevent air from being sucked back into the valve once the vacuum is released.
Locating the First Bleeder Valve
Follow the hydraulic path to determine the bleeding sequence, which typically starts with the wheel farthest from the master cylinder. For most vehicles, this is the right rear wheel. You need to access the bleeder screw, which is usually a small hex bolt on the back or side of the caliper. It is good practice to spray the screw with a penetrating lubricant and gently tap it with a hammer if it is corroded, as seized screws can break and complicate the repair. Once identified, position the catch bottle below the level of the caliper to ensure fluid flows smoothly out of the line.
Step-by-Step Vacuum Application
With the setup complete, you are ready to begin the bleed. First, pump the MityVac handle to build vacuum pressure, typically between 15 to 20 inches of mercury, and watch the gauge to maintain that level. Attach the suction end of the MityVac to the bleeder screw and hold it firmly in place. Open the bleeder screw slowly; you will immediately see fluid rushing into the vacuum line. Keep the screw open until the flow stops and the vacuum gauge indicates that pressure has dropped, signaling that the system has equalized.
Monitoring Fluid Levels and Contamination
As you work through the sequence, the fluid level in the master cylinder will drop significantly. You must monitor it constantly and add fresh fluid as needed to prevent air from entering the master cylinder. Old brake fluid can appear dark brown or black, while new fluid is usually clear or has a slight yellow tint. The goal is to continue the bleed until the fluid running through the tubing runs clean and free of bubbles. This visual check is the only way to confirm that the entire system is clean and ready for operation.
