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Brake pedal hissing after changing pads to DS2500s

Discussion in 'Suspension, Brakes, Wheels, & Tyres' started by gdw, Aug 23, 2011.

  1. gdw

    gdw

    Joined:
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    Location:
    Skelton
    Car:
    RS Clio 172
    Changed my pads and although braking is ok, probably a little better, (now using DS2500s) i'm getting a hissing noise from the pedal. I've read that the brakes may need bleeding but was under the impression that no air could or would have entered the system. The piston was pushed back using a G Clamp.

    I have been driving for a week now hoping that this would cure itself but no such luck, i've even contemplated putting my old pads back in but that defeats buying the DS2500s.

    Anyone got any ideas? should I bleed the system? do I need to do all 4 corners despite not doing changing the rear pads? when fitting, I did not undo the brake fluid cap... would that have made a difference?

    Thanks,
    Gar
     
  2. Dunn

    Dunn

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    Bleed the system

    i always do whenever ive done anything on the brakes.
     
  3. gdw

    gdw

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    I've just sprayed some WD40 on the nipples so will do it when weather looks a little more promising. I hope it is just a bleed issue, checked the fluid level and all is fine.
     
  4. sideways danny

    sideways danny

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    hissing from the pedal suggests a servo issue. Never seen that issue though, very odd
     
  5. gdw

    gdw

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    Odd yes, called a few mechanics who thought servo, one though the pads might need a better quality disc to use with the DS2500s, I thought this sounded bizarre. Like I said car brakes work but the travel and hissing is not to my liking since changing the front pads.
     
  6. gdw

    gdw

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    Just bled the system and no improvement.

    I'm going to pop my old pads in and see how I get on.
     
  7. OFFROADNICK

    OFFROADNICK

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    if its a hissing noise i would be thinking servo must be leaking air cant see that putting youre old pads back in will help but im no expert
     
  8. Fletcher

    Fletcher ClioSport Club Member

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    I can't see how DS2500 pads will make a difference.
     
  9. Geordie-Chris

    Geordie-Chris ClioSport Club Member

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    Will be servo - after you pushed the pistons back and fitted the new pads, when pumping up the pedal again after did you push it all the way to the floor or short presses till I pumped up?? I know on older cars you can damage the master cylinder seals, and wouldn't be surprised if it's somehow damaged the servo seal.
     
  10. gdw

    gdw

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    I am no mechanic I was just trying to put the car back to how it was prior to the noise. Basic fault finding on my behalf I thought.

    Just pointing out the only thing I had changed was the pads, didn't know if they were suited to the standard O.E disc.

    I can't recall what type of pumping I did... when the ignition is off the pedal pumps rock solid, just not when its ticking over.

    I've ordered some brembo HC discs because the old ones both had lips on the rear of the disc, quite severe, they actually started eating into the new DS2500s after a couple of days.
     
  11. shumoboi

    shumoboi

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    Just remove the vacuum pipe from the servo with engine running, if noise goes you know it's your servo that's the
    Problem.
     
  12. gdw

    gdw

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    ^Thanks, Is changing the servo difficult? should I have knackered it whilst changing the pads (pushing the piston back)
     
  13. shumoboi

    shumoboi

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    It's a bit of a job to do and is quite awkward mate. It shouldnt have failed by just doing a simple pad change. With the
    Engine running and foot applied too the brake pedal does the noise go?
     
  14. gdw

    gdw

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    Yes it does... Its sort of a squirt of air before it gets to a biting point. Its not a constant hiss, say you pump your foot down fast, faster then you would really do unless you had to hit the brakes for emergency stop, the pedal travels down with a hiss then the remainder of the pedal goes down normally.
     
  15. Cupman29

    Cupman29 ClioSport Club Member

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    When pushing the piston back you should open the caliper bleed nipple to prevent any brake fluid being forced back into the master cylinder as it can damage the seals. If you have abs this is a must as it can play havoc with the system.

    A lot of people won't bother but its what I've been told and confirmed by the guys at Haynes!

    Also, when pressing the pedal when bleeding and bringing the piston in contact with pads after changing pads, the pedal must be pressed slowly (3 seconds down, 3 seconds back) and the level in the resoviour must be maintained or the system can cavetate and air will enter the circuit.
     
    Last edited: Aug 28, 2011
  16. mr.pink87

    mr.pink87 ClioSport Club Member

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    Nonsense! You will have a much higher fluid pressure in the brake system when applying the brakes by foot than by pushing the pistons back in. You may damage the main cylinder seals by bleeding the brakes with the pedal instead of using a bleeding-machine but that applies to older cars and is a different story...
     
  17. Cupman29

    Cupman29 ClioSport Club Member

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    The fluid is going the opposite direction when you push the piston back into the caliper. That's what damages the seals as there would be very little pressure as its an open end in the resoviour.
     

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