Brake Booster issues

BillGrissom said

How do you diagnose "fail"? To test when you have the booster out, just connect the vac hose from another car that is running. When you push in the pedal rod, the output rod should follow w/o requiring much effort to push. It might require you pushing on the output rod to return, as the MC spring does (forgot). You will hear air leak in as it moves, but should be no noticeable hissing when stationary. Being an engineer, stating any measurement w/o units is negligent, and stating the wrong units is a major error. A probe crashed on Mars ~15 yrs ago because NASA assumed a contractor's computer thrust calculation values were in "lbf", when actually "N". Both parties were grossly negligent to ASSume.

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I remember that Mars mission. We're talking about a brake booster not a Mars mission. relax. I have a EE degree and am an aircraft mechanic, I'm no rocket scientist. I diagnose a "fail" as 'unit worked then stopped working'. It "failed" to work. The reason I have troubleshot the problem to the booster is because when the booster is replaced with a known good unit the brakes work correctly. At some point the brake pedal feels like you're pushing against a rock, there's no boost. Replace the booster, brakes work fine again, eventually I get the same results. The problem follows the booster. There is no hissing when stationary and the vacuum side holds a vacuum, which tells me the diaphragm is good. The problem has to be on the ambient pressure side. I believe we have too much throw on the pedal side and are breaking something in the booster. We're gonna tear one apart ( a bad one) and see what is broken. Sorry to have not been technical enough for you.