Lancer Shelby L4-135 2.2L SOHC Turbo (1989)
Vacuum Brake Booster: Description and Operation
Vacuum Booster Description
In order to properly service and repair available brake systems, a thorough understanding of the power assist systems is necessary. The vacuum assist
diaphragm assembly multiplies the force exerted on the master cylinder piston in order to increase the hydraulic pressure delivered to the wheel cylinders
or calipers while decreasing the effort necessary to obtain acceptable stopping performance.
Vacuum assist units get their energy by opposing engine vacuum to atmospheric pressure. A piston, cylinder and flexible diaphragm utilize this
energy to provide brake assistance. The diaphragm is balanced with engine vacuum until the brake pedal is depressed, allowing atmospheric pressure to
unbalance the unit and apply force to the brake system.
Brakes will operate even if the power unit fails. This means the conventional brake system and the power assist system are completely separate.
Troubleshooting conventional and power assist systems are exactly the same until the power unit is reached. As with conventional hydraulic brakes, a
spongy pedal still means air is trapped in the hydraulic system. Power brakes give higher line pressure, making leaks more critical.
