Express 1/2 Ton Van V8-305 5.0L VIN M SFI (1998)
Hydraulic Brake Booster: Description and Operation
Hydraulic Brake Booster Description
NOTICE: Hydraulic brake systems use two distinct and incompatible fluids. Power steering fluid is used in the hydraulic brake booster system. Brake
fluid is used in the master cylinder and brake pipes. Use extreme care when selecting brake system fluids, or seal damage can result.
Some models use a hydraulic power brake booster to provide assist. The hydraulic power brake booster uses fluid pressure from the power steering pump
to provide power assist. The power brake booster is located on the left front cowl and serves as the mounting surface for the brake master cylinder. For
unit repair of the hydraulic power brake booster refer to Hydraulic Brake Booster Overhaul (Accumulator) and Hydraulic Brake Booster Overhaul
(Check Valve).
POWER STEERING PUMP
The power steering pump supplies hydraulic pressure to operate the power brake booster. The pump is belt driven and mounts to the engine. The
power steering pump provides continuous flow of fluid to the power brake booster any time the engine is running. For more information regarding the
power steering pump, refer to Power Steering System.
POWER BRAKE BOOSTER PIPES, HOSES AND FITTINGS
Three flexible hoses route the power steering fluid through the hydraulic power brake booster system. One hose supplies pressurized fluid from the
power steering pump. Another hose routes pressurized fluid from the power brake booster to the steering gear for the purpose of power assisted
steering. The last hose returns fluid to the power steering pump. Refer to Power Steering Hose.
POWER STEERING FLUID AND HANDLING
The hydraulic brake booster system does not use special fluids. Care must be taken to use the correct fluids. The brake master cylinder and brake
system uses Delco Supreme 11 Brake Fluid, or an equivalent DOT-3 motor vehicle brake fluid, while the hydraulic power brake booster uses power
steering fluid.
Do not reuse brake system fluids. Do not mix power steering fluid with hydraulic brake fluid. Fluid contamination can result in swelling and
deterioration of rubber parts. This can lead to reduced brake performance and the eventual loss of braking capability. If the fluid is contaminated, flush
the hydraulic brake booster system with clean power steering fluid. Refer to Flushing The Hydraulic Booster System. Booster component bench
servicing should be done in a clean work area separate from the brake servicing area. Do not use the same containers for brake and power steering
fluids.
FLUSHING THE HYDRAULIC POWER BRAKE BOOSTER SYSTEM
Contamination of the fluid in the power steering and hydraulic power brake booster system requires flushing. Contaminated fluid in the power brake
booster system can cause rubber deterioration. Flushing involves draining the old fluid and replacing the old fluid with clean fluid. Clean and flush the
hydraulic power brake booster system when replacing the power steering pump. Metal shavings from a worn power steering pump often contaminate
the booster system. Disassemble the power brake booster front housing. Clean the power brake booster front housing. Replace all seals and O-ring
seals. Remove the pipes and hoses. Blow clean the pipes and hoses of all metal shavings.
