Brakes Applied
WARNING: This page does not describe the selected car, but rather 35 other vehicles, including the 1999 GMC Yukon, 1999 GMC Suburban, 1999 GMC Sierra, 1999 GMC Savana Special, and 1999 GMC Savana Camper Special. However, it is still accessible from the selected car via links, so may be relevant.
Pressing brake pedal moves pedal rod and spool valve. This closes fluid return to pump and admits fluid into boost chamber from pressure port. Additional valve movement restricts flow between power steering pump and power steering gear.
As fluid pressure increases in boost chamber, it forces piston forward, actuating master cylinder piston and applying brakes. If steering is required while braking, power steering pump pressure will rise and spool valve will shift open, allowing more fluid to flow to power steering gear.