Laser FWD L4-1997cc 2.0L DOHC Turbo (1993)
elements combined into a single power unit. The three basic elements of the single diaphragm type are:
1. A vacuum power section which includes a front and rear shell, a power diaphragm, a return spring and a pushrod.
2. A control valve, integral with the power diaphragm and connected through a valve rod to the brake pedal, controls the degree of brake application
or release in accordance with the pressure applied to the brake pedal.
3. A hydraulic master cylinder, attached to the vacuum power section which contains all the elements of the conventional brake master cylinder
(except for the pushrod), supplies fluid under pressure to the wheel brakes in proportion to the pressure applied to the brake pedal.
OPERATION
Upon application of the brakes, the valve rod and plunger move to the left in the power diaphragm to close the vacuum port and open the
atmospheric port to admit air through the air cleaner and valve at the rear diaphragm chamber. With vacuum present in the rear chamber, a force is
developed to move the power diaphragm, hydraulic pushrod and hydraulic piston or pistons to close the compensating port or ports and force fluid
under pressure through the residual check valve or valves and lines into the front and rear wheel cylinders to actuate the brakes.
As pressure is developed within the master cylinder a counter force acting through the hydraulic pushrod and reaction disc against the vacuum
power diaphragm and valve plunger sets up a reaction force opposing the force applied to the valve rod and plunger. This reaction force tends to
close the atmospheric port and reopen the vacuum port. Since this force is in opposition to the force applied to the brake pedal by the driver it
gives the driver a "feel" of the amount of brake applied. The proportion of reactive force applied to the valve plunger through the reaction disc is
designed into the Master-Vac to ensure maximum power consistent with maintaining pedal feel. The reaction force is in direct proportion to the
hydraulic pressure developed within the brake system.
