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Discussion Starter · #1 ·
Every once in awhile the brake pedal is rock hard and will not stop the car. Releasing and reapplying the pedal will normally allow the brakes to kick in, though I admit to sometimes pumping them a couple of times. I thought this was only happening while wet, but it's happened in the dry too.

The pedal does not go down at all when this happens.

We did new brakes all 4 corners 2 years ago, one new rear line last year and will be doing another now.

This happened to my old Escort years back and at some point I stole an entire booster out of a spare car which seemed to fix it, but it was so intermittent I never let it fall out of my head.

I am wondering if this can be the same issue, or maybe the vacuum modulator on the booster (I don't really know what that's called). I found one other post describing the same issue but he never said if he fixed it.
 

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If talking about the one way check valve in the booster vacuum supply line it MUST seal or you lose vacuum and why the pedal gets hard. Or booster itself has an issue with another check valve that is the release inside it.
 

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Discussion Starter · #3 ·
If talking about the one way check valve in the booster vacuum supply line it MUST seal or you lose vacuum and why the pedal gets hard. Or booster itself has an issue with another check valve that is the release inside it.
Check valve! That's what I meant of course. Is there any way to test them? I know the one for the EGT was pretty cheap, but I didn't know there was another valve inside the booster.
 

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The one in the supply line you simply suck on while not tasting the possible fuel vapor which may be in it. Then blow on it. It will flow one way but not the other. It will flow sucking on engine end of pipe or blowing on booster end but not the other way. Blow from booster end, easy to break the line getting it out of the intake.

Booster harder to tell. If you can catch it acting up then start engine and let it idle 30 seconds and shut it off, then get down by brake pedal and press it down by hand and listening carefully. You will hear a slight hiss the first 2-3 times you push down the pedal as vacuum leaks out; if pedal hard you won't hear it and already leaked out. Booster internal seal if the line has already checked out.
 
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