The brake servo, or vacuum booster, is a small canister used to increase braking pressure to take the strain off the driver's foot. If a brake servo becomes damaged or worn it should be replaced. Using the vacuum produced by your car's engine, or special vacuum pumps, the brake servo boosts the natural force sent to the master cylinder when you apply pressure to the brake pedal. This action is commonly known as power braking. A black metal canister, the brake servo is located at the back of the engine compartment on the driver's side. It sits between the master cylinder and the pedal linkage, connecting the two by means of a rod that is attached to the master cylinder's piston. A valve and diaphragm system operate the brake servo, with the vacuum on either side of the diaphragm acting as the driving force that provides the extra braking assistance. Brake servos have become commonplace with the move from the drum brake to the disc brake system (at least for the front-axle wheels), while drum brakes produce extra power by design, disc brakes require assistance with this and so use brake servos to increase braking pressure.