Brake booster kits make the job of using the brakes less strenuous for drivers of vehicles without power brakes. Most modern vehicles are equipped with brake boosters from the factory in the form of power brakes. Many older and classic cars have drum brakes and were not manufactured with brake boosters. Depending on the vehicle, some older cars may not be able to accommodate the addition of brake booster kits.
A brake booster uses vacuum from the engine to multiply the force applied on the brake by the driver. There are two types of brake boosters. Single diaphragm boosters are designed for use on cars with disc brakes in the front and drum brakes in the rear. The dual diaphragm design is used for vehicles with four-wheel disc brakes.
The brake booster must be connected to the engine with a hose to have a source of vacuum pressure. It is then plumbed to the master cylinder to use that pressure to assist with braking. A signal from the brake pedal when it is depressed engages the booster.
On many older vehicles, the brake master cylinder is typically mounted underneath the engine next to the exhaust. This leaves very little space to add a brake booster kit. Newer vehicles usually have the master cylinder on the top side of the engine located in the back along the firewall with the booster mechanism clearly visible beside it.