Stiff pedal, vacuum pump or brake booster?

Discussion in '911 Diesel Down!' started by Mammoth73, Jan 2, 2018.

  1. Mammoth73

    Mammoth73 Registered User

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    So this morning out of the blue I noticed I had little to no power brakes. Long story short the vacuum pump is showing 24Hg, the check valve is good and all hoses seem secure and leak free. Tried the booster test with pushing the pedal 5 times and holding and turning it on with little movement but it definitely sank after ignition. There is no brake light on but to be fair it doesn't come on when the ebrake is down either. My question is at this point should I just gamble on the booster? This is my daily and I don't really have the time or money to gamble with parts but at this point it's the best idea I can come up with. Any suggestions are appreciated.

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  2. snicklas

    snicklas 6.0 and Loving It!! Staff Member

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    How long does it take to build the vacuum? Is it fairly quick? My 92 had what I call a lazy vacuum pump. It would take a couple of seconds to build the vacuum. It would also only give 1 or 2 good boosts before the pedal went hard. If the ambient temperature was cold, it could take 30+ seconds to get assist....

    When you change the HVAC, do the vents change? Those run on vacuum also.

    No boost at all is either a bad pump or booster. Normally the booster will make noise if it's bad. Then ones I've had go bad make a loud woosh when you press on the pedal because of the leaking vacuum.
     
  3. Ethan Smith

    Ethan Smith Full Access Member

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    My booster was going out and didnt make no noise until i almost rear ended some old lady. If its your daily and you dont know how old that thing is you might wanna get it looked at. 300 bucks is a helluva lot cheaper than rear ending somebody
     
  4. Mammoth73

    Mammoth73 Registered User

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    I paid 75 for the booster I got at oriellys last week. Went to go to work and realized I had no power brakes. It's either your vacuum pump or the booster long story short. If you pull the hose from the booster and put your finger on it you can usually tell but not always. If it wants to suck your thumb down the pipe then its probably your booster. With mine I could tell when I pulled the vacuum hose and put my finger on it there was a noise difference coming from the pump vs it being plugged in. Which indicates a loss of vacuum somewhere in the booster. Which makes sense considering the trucks 25 yrs old and those boosters use rubber plungers (which are susceptible to rot) to get the vacuum seal. Good luck

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  5. ndnjames13

    ndnjames13 Registered User

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    Vacuum test the pump and then you'll know which way to go. I had a larger truck do this and I only like 1-2 in of mercury of the gauge. R and R'd that pump and had amazing brakes.
     

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