1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Brake Imbalance

Discussion in 'A3/S3/Sportback (8P Chassis)' started by Rom, Apr 8, 2013.

  1. Rom
    Offline

    Rom Member

    Joined:
    May 20, 2010
    Messages:
    444
    Likes Received:
    6
    [Apr 8, 2013]
    Bit if a weird one, that I've not seen as a mechanic.

    I'll start from the beginning...

    Fitted S3 front brakes, noticed they were binding. Checked on brake tester, and left caliper effort was slower than right, but overall effort was actually higher. They also binded a bit.
    Stripped out pistons, which were fine. Cleaned and lubed sliders, obviously bleed brakes.
    Binding was fixed, but still left side was slow to apply.

    I was thinking a collapsed flexi maybe, un likely, but would explain it.

    So put original brakes back on for now as I've been off work last week.

    Today, out of curiosity, I put car in brake tester with standard brakes on.
    Exactly the same results, left side applies slower, but with higher overall effort.

    Both standard and S3 are imbalanced enough to fail mot. Bit both feel fine under braking. Doesnt pull at all.

    So this has ruled out calipers, carriers, flexis.

    Anyone ever had anything like this?

    I'm now down to master cylinder, steel line, valve (assuming it has one) on bulkhead, ABS unit.
    #1
  2. Ads

    Ads

    [Sep 17, 2014]

  3. Rom
    Offline

    Rom Member

    Joined:
    May 20, 2010
    Messages:
    444
    Likes Received:
    6
    [Apr 12, 2013]
    Bump....

    Anyone?
    #2
  4. JudderMan
    Offline

    JudderMan Active Member

    Joined:
    Nov 29, 2012
    Messages:
    805
    Likes Received:
    115
    [Apr 12, 2013]
    Dirty brake fluid? Or as you mentioned a collapsed/pinched brake line.
    #3
  5. Soot1
    Offline

    Soot1 Member

    Joined:
    Jul 27, 2012
    Messages:
    184
    Likes Received:
    16
    [Apr 12, 2013]
    Are they new brake calipers or previously used?

    If new then ask the supplier for replacements. If used then you'll have to take them of and rebuild them.
    #4
  6. Rom
    Offline

    Rom Member

    Joined:
    May 20, 2010
    Messages:
    444
    Likes Received:
    6
    [Apr 15, 2013]
    They are used.

    Already stripped pistons out. Calipers are fine.

    The fact it does exactly the same with original calipers, and S3 ones means it can't be flexi, as they are different for calipers. Unless both left flexis are faulty.

    It can't be the caliper, unless with left calipers are faulty.
    Under airline pressure, pistons move the same, left pistons don't require more air pressure to move.

    Brake fluid is brand new, 5.1. And wouldnt affect just 1 wheel.

    I appreciate the input, just already eliminated all suggested. Which in fairness, is why I'm stumped!
    #5
  7. SL11CKK
    Offline

    SL11CKK Active Member

    Joined:
    Apr 22, 2011
    Messages:
    652
    Likes Received:
    29
    [Apr 15, 2013]
    Brake testing equipment maybe faulty?
    #6
  8. Rom
    Offline

    Rom Member

    Joined:
    May 20, 2010
    Messages:
    444
    Likes Received:
    6
    [Apr 22, 2013]
    Nope. You can physically watch the piston on the ns pump out slower when the caliper is off.

    Still driving fine.
    #7
  9. chris.vincent3
    Offline

    chris.vincent3 Member

    Joined:
    Apr 27, 2012
    Messages:
    608
    Likes Received:
    34
    [Apr 22, 2013]
    I'd be tempted to put braided hoses on. Bit of an expensive stab in the dark tho..

    What did you use to clamp the brake hoses? My have damaged inside the hose without any signs on the outside of the hose.
    #8
  10. Rom
    Offline

    Rom Member

    Joined:
    May 20, 2010
    Messages:
    444
    Likes Received:
    6
    [Apr 22, 2013]
    A brake hose clamp..... :)
    Same I use anytime I work on brake lines.

    That was my first thought. And if it only did this with the S3 calipers, I'd have bought a new flexi right away.
    But it does other with standard calipers and hoses.
    Which would mean I broke BOTH left flexis....
    #9
  11. max69vk
    Offline

    max69vk Active Member

    Joined:
    Apr 3, 2012
    Messages:
    760
    Likes Received:
    43
    [Apr 22, 2013]
    Have you tried purging the ABS pump unit with VCDS & done a proper bleed?
    #10
  12. chris.vincent3
    Offline

    chris.vincent3 Member

    Joined:
    Apr 27, 2012
    Messages:
    608
    Likes Received:
    34
    [Apr 22, 2013]
    Funny you say it like it was obvious. I've seen people use sockets on mole grips.

    Tried blowing air through the flexi? Might have got a bit of poo in it? Calliper isn't leaking from the join?
    #11
  13. _G_
    Offline

    _G_ Member

    Joined:
    Jul 24, 2011
    Messages:
    872
    Likes Received:
    34
    [Apr 22, 2013]
    Had the brake hose issue before, they can develop a small tear on the interior laminate that acts like a one way valve, either holding or limiting brake fluid flow. Had this on my front right last year.
    #12
  14. Rom
    Offline

    Rom Member

    Joined:
    May 20, 2010
    Messages:
    444
    Likes Received:
    6
    [Jun 24, 2013]
    I've not done a vcds bleed. Didn't know you could.

    Has been bled with a vacuum / pressure bleeder.

    There's no leaks no.
    I've not blown through the flexis, but they bleed the through OK.
    I've got it in my head it's not a flexi, as it does the same with standard brakes, and standard (not s3) flexi as well. So would mean both flexis have identical faults.
    #13
  15. infernalzen
    Offline

    infernalzen New Member

    Joined:
    Feb 13, 2012
    Messages:
    29
    Likes Received:
    0
    [Jun 24, 2013]
    i bet its the lh flexi hose.
    +the system is putting more px down the line, to compensate for it not producing the same braking effort initialy.
    #14
  16. Rom
    Offline

    Rom Member

    Joined:
    May 20, 2010
    Messages:
    444
    Likes Received:
    6
    [Jun 25, 2013]
    So you think both left hand flexis have the same fault then?

    It can't monitor pressure or braking effort from what I know.
    A master cylinder exerts x amount of force / pressure for a give pedal movement. It's just a piston pushing fluid.
    #15
  17. Lewis583
    Offline

    Lewis583 Active Member VCDS Map User

    Joined:
    Mar 15, 2010
    Messages:
    884
    Likes Received:
    70
    [Jun 25, 2013]
    Can you not swap flexi hoses left to right and see if the fault follows?
    #16

Share This Page