E 350 V10-6.8L (2007)
Vacuum Brake Booster: Testing and Inspection
Component Tests
WARNING: Use of other than the approved DOT 3 brake fluid will cause permanent damage to the brake components and will render the
brakes inoperative.
NOTE: If a vehicle with a locked wheel must be moved, loosen the bleeder screw to relieve pressure.
Always check brake fluid level and, if necessary, fill with clean, specified brake fluid.
Brake Booster
1. With the engine OFF, apply the brake pedal several times to deplete the power assist reserve in the brake booster.
2. Hold the brake pedal in the applied position.
3. Start the engine.
4. The brake pedal should drop slightly after the engine starts.
5. On vacuum brake booster equipped vehicles, if the brake pedal does not drop after the engine is started, check for vacuum at the brake booster.
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With the engine OFF, disconnect the vacuum hose and check valve at the brake booster.
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Vacuum should be heard escaping from the brake booster.
6. If vacuum is not available at the brake booster, check for vacuum at the source and check the vacuum hose for leaks.
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On vehicles without a vacuum pump, check for vacuum at the engine.
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On vacuum pump equipped vehicles, inspect the accessory drive and accessory drive belt. Refer to Drive Belts, Mounts, Brackets and
Accessories. See: Engine, Cooling and Exhaust/Engine/Drive Belts, Mounts, Brackets and Accessories
7. If vacuum is available at the brake booster and no power assist is felt, install a new brake booster and retest the system.
8. On Hydro-Boost(R) equipped vehicles, if the brake pedal does not drop after the engine is started, check the power steering pump pressure and
flow.
9. If power steering pump pressure is available to the Hydro-Boost(R) and no power assist is felt, install a new Hydro-Boost(R) brake booster and
retest the system.