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brake pedal spongy after pads change

Discussion in 'Car Repairs / Maintenance' started by jat147, 10 Oct 2008.

  1. jat147

    jat147

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    Hello,
    I recently changed the front pads on my '02 530i - which i've done on loads of previous cars. I even syringed out the excess fluid from the reservoir so it wasn't overfilled afterwards.
    Trouble is the pedal is spongy now, and travels much further than before to achieve the same force. It feels just like there is air in the lines, but i dont see how there can be?
    I'm loathe to try to bleed the system, is there any alternative?

    many thanks in advance
     
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  3. mattylad

    mattylad

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    Bleed it.

    AFAIK your only option.
     
  4. johnwr

    johnwr

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    First thing to check is, are your discs in good condition, ie are they flat, if not you will have a spongy pedal until they bed in. Is the caliper free to move?. Last of all did you buy good quality pads and not some cheap nasty compressed carboard from some back street shop.
     
  5. JohnD

    JohnD

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    new pads benefit from a couple of quite fierce brake applications.

    make sure there is nothing behind you, of course, and the road is dry and straight.

    make sure your first emergency stop is not in an emergency. the second one will be better.
     
  6. Stivino

    Stivino

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  7. jat147

    jat147

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    thanks guys,
    the discs are both good, the pads were the most expensive on the shelf.
    I checked a second time that the pistons move by pushing the pedal lots to extend them before pushing back with the Gcramp, covered by a bit of wood to push in evenly.
    Only other thing is the rubber boot round the piston wasn't seated perfectly round the back, can air get into the lines thru there? it isn't an air tight seal isit?
     
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  9. Stivino

    Stivino

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    Air can't get into the system through there as it's a dust shield. But if it doen't seal and dirt gets in then you end up with a siezed piston.
     
  10. libby lou lou

    libby lou lou

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    This advice is about right, when fitting new brakes to any vehicle, drive round the block a few times, applying the brakes, bed em in, i put my hand brake on :eek:
     
  11. Watchmaker

    Watchmaker

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    Did you use a vacuum device to bleed the brakes or, did you pump the pedal and,possibly, "stroke" the master cylinder piston right to the bottom of it's bore? It is more common on older vehicles where the master cylinder lip seal gets torn on an unpolished, corroded, and previously unused section of the bore. If you cannot resolve the problem, it is worth checking the master cylinder seals and, when re-bleeding, putting a block, under the brake pedal, to reduce it's stroke.
     
  12. Watchmaker

    Watchmaker

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    Sorry, my previous comment overlooked that you had not bled the brakes to carry out the pad change so, piston seal damage is unlikely. In these circumstances, it is most likely that there is air in the system (did you allow the reservoir level to fall too far?) and that the brakes will have to be bled.
     
  13. jat147

    jat147

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    No, the fluid certainly didn't fall much lower than than the max level, so didn't introduce air that way i think?
    This was a week ago, and have driven 200 or more miles, so the pads must be bedded in fully by now, wouldn't you think?
     
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