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Urgent - AP Racing Brake Kit Issues

Discussion in 'A3/S3 Forum (8L Chassis)' started by Yohan87, Oct 8, 2012.

  1. Yohan87
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    Yohan87 Member

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    [Oct 8, 2012]
    Afternoon all,

    Although not an Audi S3 8L, please bare with me.

    I have a 2000 (X) Registered Volkswagen Bora V6 4motion with an Audi S3 1.8T engine fitted.

    I bought an AP Racing Kit from a member on this forum, the same as this one: - AP Racing Kit - AUDI S3 1999- 4 Pot 330 mm disc 7.5x17 inch wheel

    The garage who have fitted the kit (Motorsport Specialists) are having problems getting a pedal on it and this is the latest feedback from them.

    "Do you know and have checked the sizes of the pistons in calipers are suitable for the master cylinder? My current thinking is that the master cylinder is too small for the piston area of the calipers as the pedal is just **** and hits the floor, regardless of how many times or methods you use to try bleed it. Been trying all morning with bleeding it and now it’s just getting silly. There is no air coming out of the system so fairly confident that its clear. "

    Can anybody help shed some light on the matter?

    Does the ABS pump need bled through VCDS?

    Many thanks,

    John
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  3. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Oct 8, 2012]
    Bled the master cylinder?

    <tuffty/>
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  4. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Oct 8, 2012]
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  5. Yohan87
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    [Oct 8, 2012]
    I believe they have, both nipples as well.


    Thanks tuffy, I shall pass the information on.

    The ABS unit is original, master cylinder was replaced a few months back when it was on the stock 312's and the system bled fine.
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  6. badger5
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    [Oct 8, 2012]
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  7. Yohan87
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    [Oct 8, 2012]
    Thanks Bill,

    I believe mine are from the 5200 family.

    http://www.apracing.com/product_det...-152mm_mounting_centres-16.8mm_thick_pad.aspx

    I was sure that the Bora V6 master cylinder was good for it.
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  8. Shane-Ireland
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    Shane-Ireland Member

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    [Oct 8, 2012]
    Yeah bet they haven't bled the master cylinder.I had similar size brakes on my 4mo bora with no issues
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  9. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Oct 8, 2012]
    These are the calipers by the looks..
    http://www.apracing.com/product_det...-152mm_mounting_centres-16.8mm_thick_pad.aspx

    They look to be the same piston sizes as the CP6600 calipers I have which would give a slightly longer pedal but not one thats on the deck...

    Its plausible they have flipped the seal in the MC... I don't know how they bled them but if they have used a traditional 2 man/pump pedal method at all then I suspect the issue could be this...

    <tuffty/>
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  10. Yohan87
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    Yohan87 Member

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    [Oct 8, 2012]
    Thanks for all the quick replies guys.

    Would there be any other symptoms from flipping the MC seal?

    If the calipers had been lying in my garage unused for a few months could that contribute if they are seized?
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  11. badger5
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    [Oct 8, 2012]
    if mc seal is damaged you can pump up a hard pedal evenatually (engine off) but sustained pedal pressure and it sinks to the ground.. unless its very fecked in which it just wont pump up...

    to islolate calipers from hydraulics, clamp the hoses to calipers and pedal should pump up hard and confrim hydraulics ok, but system volume @ caliper too much for the mc

    those calipers remort 38mm/41mm pistons which is same as mine..
    25mm mc on mine... whats on yours? same I would imagine

    i suspect summat else is amiss

    badly sized the other way, porka rears, is very hard pedal with poor clamping... shyte install.
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  12. Yohan87
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    [Oct 8, 2012]
    Latest update.

    "Your car only has a 23mm master cylinder, the rs3 uses a 25mm, same as the bloke below with his Ibiza. This will def give a difference in pedal. The pedal still isn’t amazing. The new calipers have a piston area of more than double the single pot caliper. Harvey has had it along the road and says he is happy with it now, so I guess the best thing is to give it a try and see how you feel with it."

    I guess all I can do is try and see.
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  13. badger5
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    [Oct 8, 2012]
    I have also used the same piston/calipers in a mk2 golf, on 23mm mc... no pedal issues.
    the fact the pedal has come better must be its bled out some entrapped air.. The pistons wont have changed size ;)
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  14. Yohan87
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    [Oct 8, 2012]
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  15. Yohan87
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    [Oct 8, 2012]
    Update 2

    "Yeah no problem. Have just come back from having a run in it myself and once bit of heat into the pads the brakes are great. :) Thankfully. Took a while but got there."
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  16. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Oct 8, 2012]
    Are the pads DS2500's? have they been bedded in properly?

    <tuffty/>
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  17. Yohan87
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    [Oct 8, 2012]
    They are indeed.

    They were bedded in using that procedure that Bill posted online somewhere.
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  18. Yohan87
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    [Oct 9, 2012]
    First impressions: -

    The pedal feels as long as it did before, only this time there is more bite once the brakes do engage. I don't see what I can do to make it harder and it had about 12L of fluid bled through it yesterday.

    The master cylinder is a few months old and a genuine VW part. When the car is off the pedal is very firm.

    I'm now wondering if it's to do with the plumbing of my brake vacuum pipe. Maybe a valve the wrong way round?

    This is the only picture I have at the moment so I'll take a close up tonight.

    [​IMG]

    I definitely don't have any boost/vacuum leaks but if that one way valve was the wrong way round, how would it affect the pedal?
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  19. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Oct 9, 2012]
    Hard pedal is normal when the engines not running... gets harder as you pump as the servo loses vacuum... pedal will sink again when the engine is started

    <tuffty/>
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  20. olethalb
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    [Oct 9, 2012]
    there's still a lot going on in that bay bud :happy:
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  21. Yohan87
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    [Oct 9, 2012]
    Agreed. But I was wondering that if I had that check valve the wrong way round if that would affect the pedal feel?

    Tell me about it.

    I need another car for a month so I can take this one off the road and tidy it up. Unless you fancy a road trip up North to blitz it one weekend :p
    #20
  22. olethalb
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    olethalb Member

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    [Oct 9, 2012]
    that would be quite a drive bud :laugh:
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  23. Yohan87
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    [Oct 24, 2012]
    Just to provide a conclusion to this thread, it appears the issue has been solved.

    Car went in for an MOT yesterday and the tester noticed that the connection between the front right brake hose / caliper wasn't as tight as it should've been and fluid was leaking out.

    He tightened it up and the pedal is definitely a lot firmer this morning, and that's without any re-bleeding of the system.

    Doesn't appear to have lost much fluid looking at the reservoir but perhaps one final bleed would be worthwhile now that the leak has been spotted.
    #22
  24. <tuffty/>
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    [Oct 24, 2012]
    Doh!

    <tuffty/>
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  25. Sevv
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    Sevv Pushing the limits..

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    [Oct 24, 2012]
    its always the bloody simplest things that go unnoticed
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  26. Yohan87
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    [Mar 6, 2013]
    Right I'm bringing this one back because I'm still not happy with the brakes.

    I have changed the following in an attempt to improve it: -


    1. New Master Cylinder
    2. New Rotors
    3. New Pads
    4. Rebled the system multiple times with varying time/mileage delays in between bleeds
    5. Replaced brake booster vacuum hose from the inlet manifold to the servo

    I still can’t even get the wheels to lock up with them!

    Does an ABS pump bleed via VCDS make any difference and is it worth trying?
    #25
  27. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Mar 6, 2013]
    Have you tried fitting a std set of calipers/discs back on? it just might be that the calipers are unsuitable?

    You could try cycling the ABS pump but have not had to do this on brake installs normally...

    Does pumping the brakes make them more effective? maybe getting pad knock off some how?

    <tuffty/>
    #26
  28. Yohan87
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    Yohan87 Member

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    [Mar 7, 2013]
    That's my next plan tuffty. Still got my stock 312mm setup so will pop them back on and see if I can get a firm pedal.
    #27

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