Brake Boosters & Master Cylinders

Having the proper type of brake master cylinder and booster for your vehicle build or replacing the aging components in your existing car or truck application will help to maximize stopping power. This includes having the correct size reservoir and master cylinder piston for drum or disc brakes as well as the correct size and type of diaphragm for your brake booster.

Upgrading the factory brake master cylinder and booster on your vehicle with a chrome, polished, or black anodized unit will help compliment the other engine and vehicle components under the hood. This will help turn more heads at the next event or show and help earn that much-deserved trophy at the awards ceremony.

A brake master cylinder is a hydraulic component, which compresses brake fluid when the driver applies pressure through the brake pedal. The brake pedal force is applied to a piston in the body of the master cylinder and pushes fluid out to the brake calipers and / or wheel cylinders to engage the brakes at each wheel. This causes the vehicle to slow down and stop.

There are several methods and items to complete in order to confirm if a master brake cylinder is functioning properly. If the brake master cylinder leaks brake fluid from a visual inspection, a master cylinder replacement or rebuild is needed. If bubbles are seen in the reservoir when the brakes are applied, an internal leak may be occurring which will require repair or replacement as well. One test that can be performed is to apply pressure to the brake pedal and hold down. The pedal should feel firm. If the pedal slowly begins to go down further while you are holding it firmly down, there may be an internal leak in the master cylinder and it will need to be inspected, rebuilt, or replaced.

Depending on the year, make, and model of the vehicle, the steps to change the master cylinder can vary. However, for most older vehicles, the first step is to remove the brake fluid from the reservoir with a suction tool. Next, unbolt the lines from the master cylinder, catching any leaking fluid as it will damage paint and surfaces if it makes contact with them. Next, remove any electrical senders or switches from the cylinder for the brake light or other devices. The master cylinder can then be unbolted from the brake booster (or the firewall if you have a manual brake application). Installation of the replacement master cylinder is the reverse of removal with two additional steps. Before installing the new master cylinder, it needs to be "bench bled" with a master cylinder bleeder kit that includes plastic fittings and hose. The fittings are tightened where the brake lines connect and hoses are pushed on to the end of them. The reservoir is filled with brake fluid and the ends of the hose are submerged into the reservoir. With the master cylinder secured in a vise or other tool, a screwdriver is used to push the piston at the back of the master cylinder inward. This pushes fluid out of the ports where the plastic fittings and hose are connected. The fluid is circulated back into the master cylinder and will contain trapped air bubbles. All air bubbles need to be removed with this process of pushing and releasing the master cylinder piston to complete bench bleeding. After the master cylinder is installed and the brake lines are connected, the brakes need to be bled at all four corners, following the specific sequence for your car or truck application (usually the furthest wheel first and the closest wheel last). The vehicle can then be carefully tested to ensure the brakes are operating properly.

A power brake booster is a component that uses engine vacuum to help assist the master cylinder in pushing the piston and fluid out to the brakes at each wheel. Inside a typical booster has a reservoir which has all air removed from a hose that is connected to engine vacuum. When the brake pedal is applied, a valve opens and allows outside air to enter the booster on the firewall side, increasing pressure to help push a rod that connects to the master cylinder piston. This makes applying the brakes easier and with less effort. If there is not enough vacuum present (usually 18-20 " Hg), the booster can't work properly and an electric vacuum pump is needed. This can be verified with a vacuum gauge. If the brake booster is leaking vacuum, one of the brake booster parts that can be tested and replaced is the check valve. The valve allows air to be removed from the booster, but does not allow air to re-enter the reservoir. If it fails, there will be no vacuum in the booster, causing it not to operate properly. It can be tested by blowing through it on both ends. It should only allow air on one side of the valve and not the other. If any internal components fail, replacement is required as there are very limited brake booster repair kit or power brake booster rebuild kit options available.