Brake in-line hose check valve operation | FerrariChat

Brake in-line hose check valve operation

Discussion in '308/328' started by Cuddy K, Jul 27, 2020.

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  1. Cuddy K

    Cuddy K Karting

    Oct 30, 2017
    181
    Full Name:
    Ian Karr
    #1 Cuddy K, Jul 27, 2020
    Last edited: Jul 27, 2020
    Hi Guys,

    Can anyone explain how the "brake booster check valve" (p/n 101538 on US QV) works...and/or how to tell if it isn't working? Of course, I get what check valves do, but this one baffles me. The direction-of-flow arrow points to the plenum, which should mean it's open under vacuum, no? If so, the only time it's "closed" is when the engine is off....which kind of negates the need for a check valve, no? TIA for your insight!
     
  2. conan

    conan Formula Junior

    Nov 13, 2011
    389
    Yes, it makes sure there is always vacuum in the brake line. It sucks out any air when throttle is closed, but closes the valve and maintains vacuum at full throttle.
     
  3. Cuddy K

    Cuddy K Karting

    Oct 30, 2017
    181
    Full Name:
    Ian Karr
    #3 Cuddy K, Jul 27, 2020
    Last edited: Jul 27, 2020
    Thanks. But isn't that contradictory? As long as the engine is running, vacuum would be pulled. I'm not understanding how it closes the valve when the flow points to the vacuum source. Maybe more pertinent is...how would you know if it wasn't working correctly...or getting stuck?
     
  4. conan

    conan Formula Junior

    Nov 13, 2011
    389
    If it gets stuck open, the brake pedal would be stiffer, harder to brake at high revs (low vacuum).

    Stuck closed would be always hard to brake.
     
  5. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    12,661
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    Mitchell Le
    Air goes one way, vacuum goes the opposite way. As an EE, I am used to thinking electrons go one way and "holes" go the other way.
     
  6. Cuddy K

    Cuddy K Karting

    Oct 30, 2017
    181
    Full Name:
    Ian Karr
    Doesn't air always flow towards the vacuum? (high to low pressure?)
     
  7. ferrariowner

    ferrariowner Formula 3

    Feb 21, 2014
    1,109
    Mansfield, TX
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    Ron
    The check valve holds vacuum for the power brake booster. Max vacuum occurs during deceleration (while in gear). You still have good vacuum at idle and at cruise. Around 12-14 inches at idle. You will have almost 0 vacuum at WOT. Without the check valve your power brakes will not work well. These valves often stick open or closed. You can usually clean them with brake cleaner if they stick. I had to replace mine, it would' clean. So they can go bad.

    Good luck.
     
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  8. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,040
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    No, at low rpm and large throttle opening, the intake vacuum falls. conan explained it correctly; however, the check valve can also get stuck closed (so no vacuum ever reaches the brake booster). Easy enough to test -- just remove it -- you should be able to blow thru it in the direction of the arrow, and not be able to blow thru it against the arrow.
     
  9. Cuddy K

    Cuddy K Karting

    Oct 30, 2017
    181
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    Ian Karr
    I think i'm getting it...the valve is designed to pass vacuum at a threshold value, and remain closed when vacuum drops below that? If the valve were stuck open, could that cause a stall on decel?
     
  10. yelcab

    yelcab F1 World Champ
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    Nov 29, 2001
    12,661
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    Mitchell Le
    Yes. So if there is high vacuum in the plenum and low vacuum in the brake line, air flows from the brake line to the plenum thereby creating more vacuum in the brake line.
     
  11. kcabpilot

    kcabpilot Formula 3

    Apr 17, 2014
    1,527
    California SF bay area
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    Paul
    The check valve means the booster remains under vacuum when the engine is off. Step on the clutch on a hill when the engine is not running and you're gonna need it. Think of it like an accumulator.
     
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  12. conan

    conan Formula Junior

    Nov 13, 2011
    389
  13. Banzairacer

    Banzairacer Formula Junior
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    Aug 24, 2017
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    Sanjeev Thohan
    Hi Steve.
    Do we have a part number for the check valve.
     
  14. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Jan 11, 2001
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    Steve Magnusson
    AFAIK, no one has identified an inexpensive, direct aftermarket replacement -- but there probably is something out there that would work as many cars use one. Try an internet search on "power brake booster check valve" or something similar.

    The Ferrari PNs are 101538 and 128435 (but the price is the typical crazy ;)).
     
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  15. kcabpilot

    kcabpilot Formula 3

    Apr 17, 2014
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    It's for the time when you press in the clutch with the engine not started and start rolling down the driveway and then step on the brake. It basically makes the brake booster a temporary accumulator so it will have a charge when you do that. You'll still get brakes if it fails but you will have to step on them real hard to stop rolling down the driveway.
     
  16. Banzairacer

    Banzairacer Formula Junior
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    Awesome - thanks again Steve you’re the best
     
  17. Banzairacer

    Banzairacer Formula Junior
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    Aug 24, 2017
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  18. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Jan 11, 2001
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    30°30'40" N 97°35'41" W (Texas)
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    Steve Magnusson
    Functionally, that looks fine. The only difference might be the OD of the fittings (10mm) seems a little small -- IIRC, the ID of the stock brake booster hose is more like 12mm (but I could be wrong).
     
  19. Ehamilton

    Ehamilton Formula 3
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    Jun 13, 2010
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    Eric Hamilton
    No power assist when the motor isn't running is the tipoff. And there's no Ferrari red magic in a yellow box stuff here, pretty much any check valve from any car with vacuum assist will work if you can fit it to your hoses.
     

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