Loss of Vacuum Boost Braking Under Panic Stops
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Thread: Loss of Vacuum Boost Braking Under Panic Stops

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    FST Member Melchior's Avatar
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    Loss of Vacuum Boost Braking Under Panic Stops

    Hi all,

    I finally got in the game, having picked up a well-kept 2013 ST3 with 75k miles. These things sure are a blast to drive.

    I caught something on the drive home that I failed to catch during my test drive. The brakes normally seem to bite really well and the pedal feel seems to be quite normal - not spongy or anything. The pads (OEM replacements) have about 40k miles on them, and the fluid was flushed about 20k miles ago. Nothing really stood out to me during my test drive.

    On the way home my heart skipped a beat as a driver in front of me forced me to do a panic stop. The brake pedal immediately went hard as a rock and I had to put all of my weight into the pedal to get the car to stop. I then did some tests on empty roads and it doesn't appear to be related to braking while the clutch pedal is depressed; the firm pedal can occur when the clutch is either in or out. It really just seems to be when I firmly slam on the brakes.

    Any obvious places to look for problems? I understand there's a vacuum pump to the right of the intake manifold and left of the air filter box, but no hoses connected to it appear to be loose.

    Any advice is greatly appreciated.

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    Supporting Member UnfocusedST's Avatar
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    Boost to brake known issue with this car. Not really an issue as the brakes do continue to work just with added effort. The vacuum pump you mention is for the factory diverter valve on the turbo.

    Sent from another garage.

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    I spend too much of my life on FST! nafsucof's Avatar
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    the vacuum pump is cam driven. it’s on the intake cam in front of the di pump.
    early build 2013. st3. blue. gen2 gtx2867. sp63 stage 1 2.3 stroker. bsd. mfactory LSD. ACT race clutch and steel flywheel. hard mounts. fswerks stealth exhaust. 3” dp. aem wmi. kirkey roadrace seat. hoosiers. a lot more stuff. custom shrouding. hoodvents. backseat delete.
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    FST Member Melchior's Avatar
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    Hmmm I did some more testing and it doesn't appear to be due to being under boost. I was decelerating to a stop sign a good 5 seconds after boost and even though the pedal felt normal at first, it suddenly firmed up on me. Very strange.

    Any ideas?

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    Quote Originally Posted by Melchior View Post
    Hmmm I did some more testing and it doesn't appear to be due to being under boost. I was decelerating to a stop sign a good 5 seconds after boost and even though the pedal felt normal at first, it suddenly firmed up on me. Very strange.

    Any ideas?

    I've had the same problem. I have drilled and slotted rotors all around with ceramic pads and at 120 mph I had minimal brakes after the initial bite. I'm suspecting brake fade due to heat. I'm waiting on some EBC yellowstuff pads.

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    FST Junkie! nickbaldwin86's Avatar
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    power brakes = brakes better while engine is at high RPMs... shift to N while coming to a stop and notice you will have "poor" braking feel. still brakes of course but you brake hard enough and can bog the engine a bit.

    Then down shift and roll to a stop and notice that the braking is better and normal feeling to a stop as long as you shift down and keep RPMs "high" (not at idle)

    just food for thought and to keep in mind.

    Also the pedal feel you are describing can be "fixed" with enough money. "fixed" not 100% . stainless lines and better fluids can help with it.

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    Does this fit what you are seeing? Or perhaps its not working as intended? Brake assist is supposed to aid in panic stop situations

    https://owner.ford.com/how-tos/vehic...ke-assist.html
    Mod list here

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    FST Member Melchior's Avatar
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    Quote Originally Posted by rambleon84 View Post
    Does this fit what you are seeing? Or perhaps its not working as intended? Brake assist is supposed to aid in panic stop situations

    https://owner.ford.com/how-tos/vehic...ke-assist.html
    Hmm interesting. I input my year and sync version and the website just gave me a video explaining brake assist. Not sure if my car has it, though.

    Even so, it definitely doesn't feel like it's helping. Every time it happened I felt as though I was gonna plow into the car in front of me or right through that stop sign, instinctively reaching for the e-brake.

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    I would check the brake pads, 40k miles is not new.

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    FST Member Melchior's Avatar
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    Yeah I figured I'd be doing a brake job some time soon anyway. There are some heat spots on the driver side rotor, too:

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