9-3 Viggen Convertible (9400) L4-2.3L Turbo (B235) HO (2001)
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 amounts to about a five-fold increase in pedal power. To
achieve this servo assistance in a compact design, the servo unit has dual operating chambers.
The servo unit is connected to the intake pipe by a hose.
The servo unit consists of a metal casing, valve unit and two diaphragms 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 acts as a single pushrod. The brakes will then be applied mechanically
without servo assistance but much more pedal force will be required.
Rest (brakes off) position