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Power brake loss after parking - symptoms of bad brake booster

Discussion in 'Stock 1995 - 2001 Explorers' started by masospaghetti, August 20, 2019.

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  1. masospaghetti

    masospaghetti Elite Explorer

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    After the truck sits for awhile, the power brakes are lost, and it's easy to unintentionally let the truck roll forward or backward while starting if you aren't really standing on the brake pedal. (Remember, this is a 5-speed stick vehicle, so to start you press the clutch -- if the e-brake isn't set or isn't strong enough, the vehicle rolls until the engine starts and provides vacuum). The brake pedal also feels hard, like there's no power boost.

    After the truck starts, everything is fine. I've replaced the little check valve on the booster but that didn't do anything.

    I assume this means there's a vacuum leak inside the booster, and the booster needs to be replaced?
     
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  3. EB4X

    EB4X Active Member

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    "After the truck starts, everything is fine."
    Maybe you're leaving something out but you will NOT have any power brakes / power assistance until vehicle is running....no vacuum....
     
  4. fast_dave

    fast_dave Active Member

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    @masospaghetti

    With my Ex, if the vacuum brake booster is OK, as well as the one way check valve and the vacuum line from the booster to the intake manifold; after 12 hours (basically overnight) there is enough vacuum left in the booster to initiate at least 1 boost assisted brake application before starting the engine.

    With the engine still off/not running, successive brake applications after the initial 1st application become harder (less boost assist) and harder.
     
    Last edited: August 20, 2019
  5. koda2000

    koda2000 Explorer Addict

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    Replace your booster. It has an internal vacuum leak. As said, even after sitting you should still have enough vacuum in reserve for one more power assisted stop before the engine starts.
     
  6. masospaghetti

    masospaghetti Elite Explorer

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    That's what I figured. It looks like the recommended method means removing the master cylinder so I'd probably replace it at the same time. Any special procedure to bleed it out? (I know sometimes the ABS modules have special requirements)
     
  7. koda2000

    koda2000 Explorer Addict

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    It used to be that MC's came with some plastic fittings and plastic hoses to bench-bleed the MC before installation. IDK of they still come with that stuff (seems to be they don't anymore). In any event you do not want to get air into the ABS pump. If you do you need a special device to force the ABS pump to run to purge the air out.

    Dorman bench bleeder kit - around $8

    [​IMG]
     
    Last edited: August 22, 2019
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  8. ptf18

    ptf18 Elite Explorer

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    Fellows.. Excuse me for this "very" silly question. But how can you tell if the Booster System is working correctly. Seems as if the brakes on my 02 Ranger require alot more effort to stop the truck than my wife's 02 S/T.
     
  9. koda2000

    koda2000 Explorer Addict

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    Sometimes when you step on the brake pedal (w/engine running) and you can hear a hissing sound. That's indicative of an internal leak in the booster.

    If when you go to start your vehicle after it's been sitting overnight and you step on the brake pedal and it feels high and hard, but drops down and feels normal once the engine is started you have a small vacuum leak somewhere, which is likely inside the brake booster (assuming your booster check-valve is working properly).

    If you know you don't have a gross vacuum leak, and you have a "hard" brake pedal and the truck requires way more pedal pressure to stop you have a leak inside the booster. In the OP's case his looses vacuum over time. This is a particular concern to him as he has a manual trans. If he had an automatic he might not even notice this issue.
     
  10. masospaghetti

    masospaghetti Elite Explorer

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    Even with bench bleeding the M/C, some air is going to get in the line when it's disconnected. I assume a "little bit" of air is OK and would not require the special ABS tool?
     
  11. koda2000

    koda2000 Explorer Addict

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    After bench bleeding the MC I try to leave the brake line fittings to the MC loose and then fill the MC it with brake fluid. I figure that should eliminate/minimize the amount of air that might get into the lines. I haven't had a problem so far.

    BTW - If you transfer your CC brake switch over from your old to new MC, keep an eye on it. When they are disturbed they can begin to leak. I had one suddenly begin leaking right after I had the CC pigtail recall done, and the only thing Ford did to it was to pop the electrical connector off and reinstall it. The switches with the red plastic center seem to be the worse about leaking. This switch leaking and shorting out is part of what caused Fords to catch fire before the recall.
     
  12. BKennedy

    BKennedy Elite Loser Staff Member Moderator Elite Explorer

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    If there is nothing wrong with your master cylinder, you don't need to replace it to change the booster. You can unbolt it from the booster and carefully push it out of the way.
     
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