Tahoe 4WD V8-393 6.5L DSL Turbo VIN S (1995)
The hydraulic pushrod operates against the master cylinder piston. A split system (tandem piston) type master cylinder is incorporated into some
units. The front half of the master cylinder in the split system operates the rear brakes while the rear half of the master cylinder operates the front
brakes.
A vacuum check valve, attached to the front vacuum chamber and connected to the intake manifold, traps vacuum in the power unit at the highest
level of vacuum.
OPERATION
As the brakes are applied by the driver, the valve operating rod and control piston move forward in the power piston assembly to compress the
valve return spring and bring the poppet valve into contact with the vacuum valve seat in the valve housing to close the vacuum post. Any
additional movement of the valve operating rod in the applied direction moves the control valve away from the poppet valve to open the
atmospheric port and admit air through the air filter and passages to the chamber at the right of the vacuum power piston assembly. With vacuum
on the left side of the diaphragm and atmospheric pressure on the right side of the diaphragm, a force is developed to move the vacuum power
piston assembly, hydraulic pushrod, and hydraulic piston to the left to close the compensating port and force hydraulic fluid under pressure
through the residual check valve and brake tubes into the brake wheel cylinders.
