Vacuum brake boosters will probably be with us for a long time. It is the most efficient and economical way to amplify the force exerted by the driver. But where the booster gets its vacuum is changing. VW has been using vacuum pumps to power the brake booster on its diesel-powered vehicles for almost 40
There are several variables that influence vacuum readings.
Most late-model vehicles use a vacuum booster to help apply the brakes. The booster is usually located behind the master cylinder on the firewall. A leak in the vent valve can cause a reduction in the performance of the booster and increase pedal travel. A manifold vacuum of 20 inHg or greater can be achieved during deceleration. The booster chambers can be evacuated and retained at this pressure by a properly operating check valve.