Tahoe 4WD V8-393 6.5L DSL Turbo VIN S (1995)
Vacuum Brake Booster: Description and Operation
General Description
In order to properly service power brake systems, a thorough understanding of the various power assist systems is necessary. These systems
provide a mechanical assist, acting to increase the force applied to the master cylinder piston by the driver while decreasing the effort necessary to
obtain acceptable stopping performance. Two basic types of power assist mechanisms are used: vacuum assist diaphragm assemblies which use
engine vacuum and in some cases vacuum from an external vacuum pump, and hydraulic assist assemblies which use hydraulic pressure developed
by an external pump (usually the power steering pump).
Vacuum assist units are similar in operation, using vacuum applied to a diaphragm or piston in opposition to atmospheric pressure in order to
increase the force applied to the master cylinder piston. However, two types of vacuum assist assemblies are used, the air suspended type and the
vacuum suspended type. Air suspended units are under atmospheric pressure until the brakes are applied, then engine vacuum is admitted causing
the piston or diaphragm to move and apply force to the master cylinder pushrod. Vacuum suspended types are balanced with engine vacuum until
the brake pedal is depressed, allowing atmospheric pressure to unbalance the unit and apply force to the brake system.
