9-5 Sport Wagon (9600) V6-3.0L Turbo (B308) (2003)
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Vacuum Brake Booster: Description and Operation
Brake servo
The brake servo unit boosts the pressure on the brake pedal exerted by the driver when the brakes are applied. The extra power supplied by the servo
unit is obtained from the vacuum formed in the engine intake manifold or vacuum pump and provides assistance in the ratio of about 5.0:1. To achieve
this servo assistance in a compact design, the servo unit has dual operating chambers.
The servo unit is connected to the intake manifold and the vacuum pump (certain variants) by means of a hose.
The servo unit consists of a metal casing, valve unit and dual diaphragm mounted between the brake pedal and master cylinder and connected to them
by pushrods. If the supply of vacuum to the servo unit fails, the two pushrods act as a single pushrod. The brakes will then work conventionally
without servo assistance but much greater pedal force will be required.
Rest (brakes off) position
