F 250 4WD LD Pickup V8-5.4L SOHC VIN L (1997)
Vacuum Brake Booster: Component Tests and General Diagnostics
1. Remove the vacuum booster hose from the power brake booster and check the valve connection. Manifold vacuum should be available at the check
valve end of the vacuum booster hose with the engine at idle speed and the transmission in NEUTRAL. If the manifold vacuum is available to the
power brake booster, connect the vacuum booster hose to the power brake booster and repeat Steps 2 and 3 of the Brake Booster Operation Check. If
no downward movement of the brake pedal is felt, replace the power brake booster.
2. Operate the engine a minimum of 10 seconds at fast idle; Stop the engine, and let the vehicle stand for 10 minutes. Then apply the brake pedal with
approximately 89 N (20 lbs) of force. The brake pedal feel should be the same as that noted with the engine operating. If the brake pedal feels hard
(no power assist), replace the check valve and retest. If the brake pedal feels spongy, bleed the hydraulic system to remove air; refer to hydraulic
system Service and Repair for system bleeding procedures.
