power brake booster/how too check

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alsdemon

alsdemon

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is there a way to check a power brake booster off the car/truck? it does not run yet and looking to buy a junk yard one / i have a mighty vac that i can apply vacumn with.
 
Apply a vacuum of 16 - 18 "Hg (this will take a bit with a hand held mighty-vac) and see if it holds for 2-3 minutes. If so, the shell is not leaking and the atmospheric valve is sealing when closed. Now apply the pedal - if the pedal sinks away with assist and there is a brief, slight hissing or 'huffing' noise inside the vehicle but applied vacuum holds at the previous level, then the vacuum valve is closing properly, the diaphragm is not torn or leaking and the atmospheric valve is opening properly. When you release the pedal, the applied vacuum should drop by several inches of Hg as the vacuum valve opens and the air in the atmospheric chamber bleeds over into the vacuum chamber. If all the tests pass, the booster is likely good - only thing you have not verified is the condition of the return springs on the diaphragm and poppet valve assembly. If any test fails, seek a different unit...
 
Sorry - forgot you said off the truck - push on the input rod instead of pressing on the pedal. Air will be taken in through the filter surrounding the pushrod. You will need to push a drum stick or similar dowel in from the master cylinder end at the same time to provide an opposing force to your input - otherwise the reaction disc will not compress and the poppet valve (vacuum and atmospheric valves) may not operate correctly (plus you need to be able to feel if the booster is providing assist.)
 
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