Mustang V8-4.6L DOHC (1996)
Hydraulic Brake Booster: Testing and Inspection
Hydro-Boost System
Ensure engine is OFF, then press and release the brake pedal several times to relieve all hydraulic pressure from the booster. Depress and hold the pedal
with light pressure. Start engine and note pedal reaction. If it does not fall slightly and hold, press and release the pedal several times, then depress and
hold with medium foot pressure. If the pedal now moves toward the floor, inspect for brake fluid leakage at master cylinder, brake hoses and all
connections.
To inspect the Hydro-Boost unit for leakage, idle the engine, then depress and hold the brake pedal for no more than five seconds with heavy foot
pressure. If the booster shows any signs of fluid leakage, it must be replaced.
An accumulator reserve retention inspection requires operating the engine at idle, then depressing and holding the brake pedal for no more than five
seconds with heavy foot pressure, or holding the steering wheel at full stop. Turn the ignition OFF, then wait 8-12 hours. Depress the brake pedal and
inspect for reserve. If no reserve is present, the booster is defective and must be replaced.
POSSIBLE REASONS FOR NO POWER ASSIST:
1. Power steering pump drive belt slipping or worn.
2. Power steering pump fluid level improper.
3. Linkage binding.
4. Hydro-Boost unit failure.
POSSIBLE REASONS FOR ERRATIC BOOSTER OPERATION, BINDING, GRABBING OR STICKING:
1. Supply hose leakage or obstructions.
2. Hydro-Boost unit seal leakage.
