If your vehicle’s brakes do not seem to be as strong as they once were, the likely cause is the brake booster master cylinder. The brake booster master cylinder is a part of the break system that controls how quickly the brakes take effect when the pedal is pressed. The booster uses a vacuum from the engine to increase the force applied by the breaks when the pedal is pressed. This relates to a much quicker stop of the vehicle, with little pressing required. If the pedal has to be pushed all the way to the baseboard before you begin to feel the breaks take effect, you will most likely need to replace or repair your brake booster master cylinder. This article will walk you through the steps of doing just that.

Step 1 – Remove the Master Cylinder

The master cylinder will be located in the driver side firewall inside the engine bay in front of the brake booster. There will be two small tubes coming out of the side of the master cylinder that need to be removed. If necessary, apply WD-40 to loosen the nuts and remove them completely. Use your vice grips if needed and expect a small amount of brake fluid to come out. Then you can take out the sensor wire and the nuts attaching the cylinder to the booster.

Step 2 – Attach the New Master Cylinder

Drain the break fluid from the reservoir into your waste can. Attach the hoses that you have from the cylinder into the reservoir. Prime the unit to push the brake fluid through the system enough to remove as many air bubbles as possible. Once this is done you can then reattach the new master cylinder to the brake booster and clean away any spilled fluids. Replace your priming tubes with the original tubes as they were originally.

Step 3 – Bleed the Brakes

The next step is to go to each wheel and bleed the brake fluid. Start with the rear passenger side tire and remove it. Make sure the car’s parking brake is engaged and parked on level ground. If possible, place a block behind the other tires to prevent the car from rolling or shifting while the car is raised. Once you have the tire off locate the bleeder valve on the drum or caliper. Open the valve slightly while the other person pumps the brake pedal 3 to 4 times. Bleed the fluid out of each tire on the vehicle until there are no more air bubbles.

Step 4 – Test the Brakes

The last step once all of the tires are put back on is to remove the jack and turn the ignition to start the car. Press the brakes in a few times and make sure they feel tight and stiff. If the brakes feel tight enough the new brake booster master cylinder is good to go.