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Brake Imbalance

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

  1. Rom
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    Rom Member

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    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.
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  2. Rom
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    Rom Member

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    Bump....

    Anyone?
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  3. JudderMan
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    JudderMan Member

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    Dirty brake fluid? Or as you mentioned a collapsed/pinched brake line.
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  4. Soot1
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    Soot1 Member

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    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.
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  5. Rom
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    Rom Member

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    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!
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  6. SL11CKK
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    SL11CKK Member

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    Brake testing equipment maybe faulty?
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  7. Rom
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    Rom Member

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    Nope. You can physically watch the piston on the ns pump out slower when the caliper is off.

    Still driving fine.
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  8. chris.vincent3
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    chris.vincent3 Member

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    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.
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  9. Rom
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    Rom Member

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    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
  10. max69vk
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    max69vk Member

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    Have you tried purging the ABS pump unit with VCDS & done a proper bleed?
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  11. chris.vincent3
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    chris.vincent3 Member

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    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?
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  12. _G_
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    _G_ Member

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    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.
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  13. Rom
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    Rom Member

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    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.
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  14. infernalzen
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    infernalzen New Member

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    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.
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  15. Rom
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    Rom Member

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    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.
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  16. Lewis583
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    Lewis583 Member

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    Can you not swap flexi hoses left to right and see if the fault follows?
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