09 Expy EL Vacuum loss to power brake booster at speed

11b4v · Aug 31, 2016

All,

2009 Ford Expedition EL. Replaced both the power brake booster and master cylinder recently; master cylinder was leaking into the booster. Before, and after, at highway speed, or on/after heavy acceleration, I lose vacuum boost to the brake booster and experience a hard brake pedal.

Any suggestions as to what part of the vacuum system is the culprit?

Much thank in advance for your assistance,

docraymund · Aug 31, 2016

If there are no vacuum leaks present and the hoses are tight you may have bought a defective master cylinder or booster.

11b4v · Sep 6, 2016

I'm thinking the new booster is good, I'm thinking either a vacuum line check valve(s) or maybe a leaking hose that goes at speed/higher pressures.

The Swagonmaster · Sep 14, 2016

There is always a vacuum check valve in the booster vacuum line to prevent exactly what you are describing. Check it to be sure that the vacuum that is there at idle (which is high) is still there when you open the throttle (when vacuum is low).

09 Expy EL Vacuum loss to power brake booster at speed

11b4v

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The Swagonmaster

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