Disc brakes, unlike drum brakes, do not work with a self-reinforcing effect: they require significantly more pedal force. Therefore, the Vectra has an air brake booster that generates about 60% of the braking force.
This accessory is located on the left side of the engine compartment behind the brake master cylinder. But the brake pedal is directly connected to the brake piston of the master brake cylinder, so you can brake even with a failed auxiliary device. But in this case, the required pedal pressure must be increased many times!
Assistance is provided by reduced pressure in the intake manifold. The brake booster is connected to the intake manifold by a hose. When braking, the difference between atmospheric pressure and reduced intake manifold pressure displaces the large elastic diaphragm and puts additional pressure on the pistons in the brake master cylinder.
If the engine is not running, the brake booster also cannot develop (additional) braking force. Therefore, you must press harder on the pedal if, for example, your vehicle is being towed. If the engine suddenly stops on the road, then you still have some reserve for a few short decelerations - only after that the calf muscles should work at full strength.
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