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Brake Servo Issue?

Discussion in 'A4/S4 forum(B5 Chassis)' started by tux, Jan 28, 2011.

  1. tux

    tux Member

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    Hi all, once again I find myself needing to call on your collective wisdom. I've had a trawl about with the search function and got some tips, but still missing a few bits of info.
    I did a track day at Silverstone on Sunday, the first in the A4 (1998 2.4 V6 saloon) and I found after about 3 laps I was getting epic brake fade and the pedal getting very soft and spongy. A 10 minute break and all was well again for another couple of laps, when the issue re-occurred.
    Disks and pads are new up front (standard items) and the calipers seem to be free enough, so don't see too many issues there.
    If I pump the brake pedal with engine off it gets hard as expected, but if I then turn on the engine it doesn't sink as I would expect. I can also hear a "hissing" sound at this point until I release the brake pedal. Not sure what to make of that.
    The brakes are good enough (though not brilliant) on normal road driving.
    So I guess my questions are: Is the servo goosed? Are the brakes usually "average" on an A4 or does it sound like somethings amiss? Am I expecting too much from the braking system? Are there any common/likely issues that I should be looking for?
    Also, if I have to replace the servo, there is mention in Elsawin of needing a VAG tool to bleed the clutch after disturbing the brake master cylinder, is this the case or is there a DIY version? Vacuum bleeder perhaps?
    Thanks in advance guys and gals.
     
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  3. aragorn

    aragorn "Stick a V8 in it!"
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    The stock brakes just arent up to track use, especially if still on standard fluid and pads.

    Spongy pedal indicates you were boiling the fluid, which may also be made worse if the fluid is old.

    As a very minimum you need to flush the fluid out and replace it with something better, and fit some track capable pads, like the DS2500's or Mintex M1144's

    The next step after that would be to fit larger brakes, unfortunatley the only bolt on upgrade is a set of S3/TT carriers, which allows you to go from 288 to 312mm. Not fantastic, but better than nowt.

    If you want to go bigger still, then you need to swap your front uprights for either S4 or B6A4 items, and then you can use either 321mm B5 S4 disks and calipers, 345mm B6 S4 disks and calipers or any number of other combinations.
     
  4. tux

    tux Member

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    How did I know that you would be first to answer! :laugh: Thanks dude.

    You don't think the servo sounds iffy then?
     
  5. aragorn

    aragorn "Stick a V8 in it!"
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    Not really. If the servo was duff the pedal would be wooden and you'd be up out your seat trying to stop the car from 30mph.
     
  6. Oranoco

    Oranoco Well-Known Member

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    Sounds like old fluid and brakes that aren't really up to the stick track driving gives. My 1.8TH only manages 6 laps or so at Bedford before I need to have a warm down lap and come off.
     
  7. murran

    murran Active Member

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    servo shouldnt be hissing either way.
     
  8. tux

    tux Member

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    Thanks y'all!
     

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