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458 stiff brake pedal after engine start but ok afterwards

Discussion in '458 Italia/488/F8' started by action-ant, Sep 16, 2019.

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Does your brake pedal go stiff (no pedal travel) after starting the engine?

  1. yes and it returns to normal feel and travel after moving the car a few feet

    57.1%
  2. nope

    42.9%
  1. action-ant

    action-ant Karting

    Nov 16, 2015
    163
    San Francisco, CA
    Full Name:
    Anthony
    Hey guys,

    I took the car out to PCH this weekend and had the brakes act weird at least twice upon vehicle startup. The brake pedal felt fine and had some travel when I pressed on the brakes before pressing the engine start button (engine is off). Once the engine is running, when I press the brake pedal again to engage reverse gear, the pedal is stiff with very little travel (as if no vacuum assist available). I backed the car slowly a few feet and when I pressed on the brake pedal, it felt fine and had normal brake travel and feel. This happened at least twice when starting the car and reversing out of the parking spot. It did not occur at speed or while moving. I tried to see if I could get the dead brake pedal when stopped at a stoplight and depressed the brake pedal off and on repeatedly and quickly. I didn’t get a dead stiff pedal but did detect slight difference in pedal firmness and maybe travel-I figured maybe this was due to quick repeated brake presses and vacuum wasn’t building up quickly enough in between brake presses. Has anyone seen this on their car?

    There’s a vacuum hose assembly that is shaped like a “Y” that connects into each intake manifold and then joins together and plugs into another main line that runs along the bottom of the car towards the front. This hose assembly looks to have two check valves, one for each manifold. I’m wondering if it’s possible to disconnect at one manifold and apply vacuum and check for leaks and repeat for the other side? I am not sure if the hose assembly is accessible and can be replaced. The other area could be brake booster underneath the windshield wipers, but I am not sure why or how I am getting a hard brake pedal after the engine first starts, but seems fine afterwards.

    Any help would be appreciated!

    Ant
     
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  3. eric355

    eric355 Formula Junior
    Silver Subscribed

    Nov 30, 2005
    977
    Toulouse (France)
    Full Name:
    Eric DECOUX
    May be the AVH function (Automatic Vehicle Holding) ?
    When it happens, do you have the "HOLD" message in the tacho display ?
    If yes, that's normal, the car is temporarily braking by itself to stay stationary until you apply some throttle. In that case the brake pedal is stiff.
     
  4. action-ant

    action-ant Karting

    Nov 16, 2015
    163
    San Francisco, CA
    Full Name:
    Anthony
    Hi Eric,

    Hmm I don’t recall if AVH is holding the car temporarily. Even if it was, doesn’t that utilize the parking drum brakes in the rear and not hydraulic pressure on the main brakes? I’ll take a look later and see if the brake pedal feels differently with AVH engaged or not.

    Thanks Eric,

    Ant
     
  5. action-ant

    action-ant Karting

    Nov 16, 2015
    163
    San Francisco, CA
    Full Name:
    Anthony
    I’ve uploaded a quick video showing the brake behavior this past wknd-happened at least twice.

     
  6. MalibuGuy

    MalibuGuy F1 Veteran

    Sep 18, 2007
    5,037
    Malibu, CA
    I’ve had this happen as well. I imagine it has something to do with the amount of vacuum assist.

    At first, I had some difficulty engaging reverse to back up. So I shut down the car and restarted.

    But even if the pedal is stiff, just use a little more force and you should be able to engage a gear.

    It is possible that the brake pedal sensor might be malfunctioning.
     
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  8. rlips

    rlips Formula Junior

    Jul 29, 2011
    955
    New Jersey, USA
    I have a 458 challenge car, which is pretty similar. Had to replace the brake booster and master cycle day; fairly easy job. I was told they are a common point of failure.
     
  9. eric355

    eric355 Formula Junior
    Silver Subscribed

    Nov 30, 2005
    977
    Toulouse (France)
    Full Name:
    Eric DECOUX
    Ant,
    when the AVH function hold the car temporarily, eg. for a start on an incline, to allow for some time (a few seconds) to get on the throttle, it uses the main brakes.
    In that case, "HOLD" is displayed and the pedal is stiff. I have experienced that many times because of my garage configuration.
     
    action-ant likes this.
  10. action-ant

    action-ant Karting

    Nov 16, 2015
    163
    San Francisco, CA
    Full Name:
    Anthony
    Eric, you're the man. You were spot on--when AVH is engaged, the main brakes are used to keep the car in place and results in a stiff pedal with little travel. Thank you!
     

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