Car brake help – 'sinking' pedal

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  • Car brake help – 'sinking' pedal
  • Premier Icon bails
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    It’s a Ford Focus, the brakes still work (in the most basic sense, they stop the car), the discs and pads are both relatively new, the whole system was recently bled with new fluid.

    But when I hold my foot on the brake with the engine running the pedal sinks down. I can pump the pedal and it firms up. If I hold the pedal while the engine is off then it doesn’t seem to ‘sink’.

    I can’t see any fluid leaks and from the level on the reservoir it doesn’t look like any fluid has been lost.

    So is this normal, or is there likely to be a fault somewhere? (master cyclinder?)

    peterfile
    Member

    Are they Avids?

    Premier Icon bails
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    Premier Icon wwaswas
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    could be that the brake servo is leaking air which would explain why it happens when the engine running.

    They may just need a bleed though and you don;t experience the sinking pedal as much with the engine off because you’re not putting so much pressure into the system by leg power alone?

    trail_rat
    Member

    sounds like a classic master cylinder to me tbh if you arnt losing fluid.

    Premier Icon gibber
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    I had my focus serviced (by a “professional garage”) and they got dirt in one of the o-rings. Push pedal and it just kept going. Pump and it got a bit firmer, but made a big puddle of brake fluid on the floor. Took it straight back and made sure it spilt the rest on their forecourt.

    If you can get it to a point where you can really push on it hard and it wont move (i.e. full force you can do), then its probably not leaking, but I would go and get it checked – don’t p*** about with tyre and brakes, you want them to work when you need them.

    My one does have a bit of squish when the power assist kicks in, but its not like you have to pump it many times (maybe an inch).

    I’d say servo air leak.

    With the engine off, pump the brake pedal until it goes hard (oo-er missus). Keep your foot on the pedal and start the engine.

    As the servo kicks in the pedal should sink slightly then stop. If it continues to sink then suspect either a damaged vacuum hose to the servo or a leaking joint.

    trail_rat
    Member

    another thing i would look at is your brake flexies

    possible and common that one of them is faling & bulging under pressure.

    any of the above tbh – you want to be getting it to the garage and have them check it out.

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