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Still got brake issues

Discussion in 'A3/S3 Forum (8L Chassis)' started by BlackQuat, Mar 20, 2010.

  1. BlackQuat
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    BlackQuat Well-Known Member VCDS Map User

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    [Mar 20, 2010]
    Y Reg 2001 Audi A3 100bhp TDI

    Put the new caliper on today, fully bled the system. Including the master cylinder.
    With the engine off, its firm as you like, rock solid from the top.
    With the engine on it's spongey. Also if you keep your foot on the brake, it goes to the floor and eventually the revs dip.

    This leads me to think there is a vacuum leak. I've disconnected and sealed the branch off from the valve just after the vacuum pump. But it still does it, so this would suggest the leak is on the solid pipe to the servo, but i find that hard to beleive.

    Anyone had this before?

    Cheers in advance.
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  3. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator VCDS Map User

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    [Mar 20, 2010]
    The A3 brakes are notoriously bad to bleed. Give another go, and another and another. It will eventualy come up.

    How are you bleeding? Pumping,easibleed or vacuum bleeding?
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  4. BlackQuat
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    BlackQuat Well-Known Member VCDS Map User

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    [Mar 20, 2010]
    Pumping the brakes. I don't have a pressure bleed and idealy would like to avoid having to buy the kit.

    What makes them so bad to bleed?
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  5. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Mar 20, 2010]
    Pressure bleeder mate... you stand a chance of buggering the seals in the master cylinder if you pump them.

    Gunsons EEZI Bleed... get one from Halfrauds or ebay, costs about £15 and will save your life... quite literally...

    Also need to bleed the master cylinder once the brakes are done...

    <tuffty/>
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  6. BlackQuat
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    BlackQuat Well-Known Member VCDS Map User

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    [Mar 20, 2010]
    I might have to buy one. Means mooooooore fluid to buy lol.
    I did the master cylinder too.
    I think I'll just have to get one :(
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  7. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Mar 20, 2010]
    Its the best way to bleed them tbh... well worth the investment as you will need to change the fluid every 2 years anyway...

    <tuffty/>
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  8. beachbuggy
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    beachbuggy Well-Known Member

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    [Mar 20, 2010]
    You will definately benefit from using an pressure bleeder and for £15 will save you a whole lot of hassle and easy for one person to use.

    I don't agree with the addage that if you let the fluid fully drain and put the peddle to the floor you're flip the seal and knacker the master cylinder. I've seen a seal in the rear cailper pop, all the fluid drained and the resevour and MC was completely emptied. The peddal still worked fine after it was refilled and bled. This is only my opinion and if anyone can show me a flipped seal then I will change my mind:yes:

    Also depending on how much fluid came out, an ABS cycle could be needed but this is only in the advent in the fluid being drain from the MC and air getting into the ABS pump. Only way to do this is to use VAG-COM but like I say for a caliper change you almost certainly wouldn't have to do this.

    As previously stated it's likely you still have air in the system. Use a pressure bleeder and your stand a good chance of getting all the air out, even a small bubble will cause a problem.
    Last edited: Mar 20, 2010
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  9. Broken Byzan
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    [Mar 20, 2010]
    That is not an addage, it's a fact, i have seen it happen and had to change the MC because of it. Just be aware is all i will say, it's unlikely, but possible. Mostly due to surface rust on the piston/cylinder from where the piston doesn't normally travel, it's just enough to flip or tear the seal
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  10. BlackQuat
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    BlackQuat Well-Known Member VCDS Map User

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    [Mar 20, 2010]
    I'm wondering if its already happened.
    Might source a fresh MC
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  11. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Mar 20, 2010]
    Try the pressure bleeder first... new MC's are around £200 from Audi and around £100 from GSF... and you will still need to bleed it afterwards...

    <tuffty/>
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  12. BlackQuat
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    BlackQuat Well-Known Member VCDS Map User

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    [Mar 21, 2010]
    I've woke up with this on the mind, i just can't help but wonder why the revs dip if you keep your foot hard on the peddle. As it lowers to the floor, the revs dip slightly.
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  13. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Mar 21, 2010]
    Had a similar issue with a BT A3, checked the one way valves and all ok... the servo draws a vacuum from the inlet mani so it may be that the servo has a leak somewhere but couldn't find one in the A3... brakes worked fine though and nothing came up in VAGCOM.

    I can't say I have noticed it myself as I don't dip the clutch when I brake (unless its an emergency stop) so maybe they all do it...

    Priority of course is to get the pedal up, pressure bleeder, job done :)

    Had a guy come in with a TT he had fitted 6 pot brembos... pump bleed them and got no where... pedal would sink straight to the floor... told him to pressure bleed them which he did and all was good... it works... simples :)

    <tuffty/>
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  14. BlackQuat
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    BlackQuat Well-Known Member VCDS Map User

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    [Mar 21, 2010]
    Such a odd thing isn't it! lol
    I think i'll get one then, like you say it'll only need doing again in 2 years, plus i can do the A4 sometime too.
    Thank you all for your help, even if i am slow on the uptake ;)
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  15. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Mar 21, 2010]
    lol, no probs mate... first time I bled the brakes on my S3 I used the pump pedal method and they were ****... they work quite well now :)

    <tuffty/>
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