At the heart of any power brake upgrade is the power brake booster. The power brake booster is a device that mounts to the vehicle's firewall, located behind the brake master cylinder. It gets its power from the vacuum created by the engine when it's running. You may have noticed on a car with power accessories that the steering wheel is difficult to turn and the brake pedal is hard to press - that is, until you turn the key and crank the engine. Once the engine is running, these features are able to operate as intended -- with minimal effort.
A power brake conversion kit may also include a new brake pedal. The new pedal will have to travel a much shorter distance to effectively stop the vehicle.
Other pieces that may come new with your particular kit include brake fluid reservoirs, a brake force distribution block and perhaps a proportioning valve that determines how much braking force goes to the front and the rear wheels.
Vacuum-assist brake boosters are the most popular types on the market, but they aren't the only kind. In fact, in some cars the vacuum pressure created by the engine is too weak to provide effective braking force. One way around this is to create an all-hydraulic, or hydroboost, system. In these setups, the brake system borrows pressure from the power steering pump to provide the additional stopping force [source: Nelson].
These setups presume that the vehicle has power steering in the first place. In the days that spawned today's classics, power steering was considered a luxury, but the aftermarket has stepped in with power steering kits as well.
Vacuum-assist and hydraulic-powered controls may one day become obsolete. For future generations of cars, manufacturers are developing fully electronic braking systems that are more responsive, weigh less and can use on-board computers to brake more effectively than current braking systems.
To find out the steps in installing a typical power brake conversion kit, go to the next page.