The black, round canister mounted on the firewall at the back of the engine on the right driver’s side under the hood is the brake booster.
Since most cars now have disc brakes, power brakes are necessary to assist in multiplying the power exerted by the driver’s leg/foot. The force applied by the driver’s foot to the brake pedal is multiplied in the power booster. The power booster multiplies the force using a vacuum created by the engine.
The best method to determine if the brake booster is functioning properly is the following:
With the engine turned off, press and release the brake several times to assure there is no vacuum remaining in the booster
Using a fairly firm foot, hold down the brake pedal and turn on the engine
When the brake booster is functioning as it should, you will feel a slight give underfoot as the engine turns over.
The master cylinder and brake booster are replaced, removed and repaired as a single unit. If you have decided to do the installation of the master cylinder and brake booster assembly yourself there is one important item you should note. Often the master cylinder is filled with brake fluid before it is installed. Brake fluid is very damaging to paint so be sure to appropriately protect your car’s paint before filling the master cylinder with brake fluid any where near your vehicle.
If you are converting a SUV to larger tires, you will need to consider your braking system as well. Now would be the time to upgrade to a larger brake booster and master cylinder assembly for the extra stopping power you will need. Today’s larger and heavier vehicles definitely should have upgrades on their boosters and master cylinders to be safely driven on the streets. This is a complicated conversion and will require specialized tools so please don’t attempt if you are not fully prepared.
Since brakes are the single most important system in your vehicle, always consult with a specialist when upgrading anything to do with the tires, suspension or brakes in case you also need to upgrade your braking system. Also, anything changing dramatically the weight of your vehicle, such as trailers should be checked for necessary braking upgrades.