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Brakes causing vacuum/boost issues.........

Discussion in 'A3/S3 Forum (8L Chassis)' started by Dani_B19, Feb 27, 2012.

  1. Dani_B19
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    Dani_B19 Audi-sports own special child.

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    [Feb 27, 2012]
    Right.

    Pulled up from work today, parked the car up the drive and let it idle for a minute or 2, but for some reason i pressed the brake to which i noticed the boost gauge move.
    The car idles bang on 20 inhg without any movement on idle now but, when i started to press the brakes, the vacuum was creeping up to 17/18 inhg, if i kept pressing the brake the needle would just keep flicking up and down between 20 and 17 inhg.

    Now to me this isn't normal and shouldn't happen, it should sit bang on 20 inhg regardless of the brakes!

    I do remember Andrew having to replace the brake pipe behind the heat shielding next to the bulk head, cant remember what the proper name for it is, could this be at fault?
    #1
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  3. jay1601
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    jay1601 Well-Known Member

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    [Feb 27, 2012]
    its normal. the brake booster runs off the vacuum system (normally pipe coming off the intake manfiold)
    #2
  4. Dani_B19
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    Dani_B19 Audi-sports own special child.

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    [Feb 27, 2012]
    So does yours do this jay?
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  5. jay1601
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    jay1601 Well-Known Member

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    [Feb 27, 2012]
    mine will go between 18-21depending on throttle load, gear, braking, ect.
    #4
  6. Dani_B19
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    Dani_B19 Audi-sports own special child.

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    [Feb 27, 2012]
    What on idle? Surely if the cars sat idling then the idle shouldn't move.
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  7. jay1601
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    jay1601 Well-Known Member

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    [Feb 27, 2012]
    when on idle (no brakes or clutch/gears) will sit bang on 20
    #6
  8. Dani_B19
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    Dani_B19 Audi-sports own special child.

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    [Feb 27, 2012]
    yeah thats what i mean mate. I was sat on the drive earlier in neutral and then the above as post 1# started happening which to me doesnt seem right.
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  9. S3featesV9
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    S3featesV9 Active Member

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    [Feb 27, 2012]
    Mine never sits bang on 20? Always about 16inhg. What would this indicate. Also it fluctuates when steering wheel is moved, even at idle :s
    #8
  10. Dani_B19
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    Dani_B19 Audi-sports own special child.

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    [Feb 27, 2012]
    MAY JUST BE YOUR GAUGE MATE, BUT YOU WANT IT TO SIT AROUND 18 TO 20 INHG, IF LOWER THEN NORMALY MEANS A VACUUM LEAK ETC.
    MINE DOESNT DO THAT WITH THE STEERING WHEEL.
    #9
  11. Dani_B19
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    Dani_B19 Audi-sports own special child.

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    [Feb 28, 2012]
    So anyone else any thoughts?
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  12. Alais DJA
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    Alais DJA Member

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    [Feb 28, 2012]
    Turn on your heaters

    Open your electirc windows

    Turn on full beams....... it always drops a tad
    #11
  13. Westy
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    Westy Double Dark Side! Diesel & 8P

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    [Feb 28, 2012]
    Nothing to worry about mine is exactly the same.
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  14. S3featesV9
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    S3featesV9 Active Member

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    [Feb 28, 2012]
    Yeah. All good and bill said it should fluctuate when steering wheel is moved as it putting load on the engine.

    One less thing to worry about
    #13
  15. Dani_B19
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    Dani_B19 Audi-sports own special child.

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    [Feb 28, 2012]
    Thanks lads.
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