955 Juddering Under Hard Braking?

Discussion in 'Technical Help' started by scotdoc, Mar 9, 2020.

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  1. scotdoc

    scotdoc New Member

    Jan 15, 2017
    5
    3
    Crewe
    A minor but annoying issue with my 2005 955i Daytona, 26,000 miles
    When I brake heavily I get a mild juddering from the front end.
    The tyre is fairly new and balanced
    The forks have been serviced and set up for my weight
    I checked the head races with the wheel out and didn't detect any laxity or notchiness moving side to side
    The discs are within tolerance without any obvious grooving or run out

    The brake pads are near the end of their life and I will fit some new ones shortly.

    The only other thing I wondered was if the disc bobbins might be wearing?

    Anything else I should check out? Thanks for any advice
    Russ
     
  2. Rocker

    Rocker Elite Member

    May 1, 2016
    1,659
    800
    Suffolk
    Sounds like head stock bearings
     
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  3. freck

    freck Elite Member

    May 4, 2017
    1,719
    750
    Preston, Lancs, UK
    It might be worth giving the brake disc bobbins a clean out, making sure they’re not seized up.
    I’d give the calipers a good clean up too if you’re changing the pads. :grinning:
     
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  4. scotdoc

    scotdoc New Member

    Jan 15, 2017
    5
    3
    Crewe
    Thanks
    Just stripped and changed seals on calipers so all pristine
    I thought about head bearings but they move freely side to side and there is no play back/forward or sideways with the wheel out? The sensation is of a recurrent mild knock not just when the brake applied.
    Could they be loose if the adjuster nut isn't set properly? It was looked at a couple of years ago when I had the to yolk off
     
  5. Callumity

    Callumity Elite Member

    Feb 25, 2017
    3,355
    800
    Nr Biggar
    You really need the front wheel elevated and grasping lower fork leg check for any fore and aft play. The bobbins want spinning to ensure lateral free float and to shift any fine dirt.
     
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  6. DanielB

    DanielB Noble Member

    Jan 13, 2019
    865
    393
    Abingdon, Oxfordshire
    As a 'hunter and gatherer' of motorcycle mechanictry....trying learn as I go, I have heard that the bobbins being cleaned and being free to spin is good and necessary maintenance, through to not necessary...

    So, just to be changed l clear - and I have more trust in this site than others - is it indeed the case that I should be looking to free up the bobbins so they spin freely?

    Why is this? Is it because the disc needs to be able to float?

    Isn't the disc pinched on both sides equally but the pistons - which is why the pistons need to be clean and moving freely and equally under fluid pressure?

    Thank you!!
     
  7. freck

    freck Elite Member

    May 4, 2017
    1,719
    750
    Preston, Lancs, UK
    Yes you’re right Daniel. The bobbins need to be free to allow the slight movement between the disc and the fixed rotor they’re attached to.
    This float is to allow for some axial and lateral movement to compensate for manufacturing tolerances, allowing a better pad contact therefore better braking efficiency and more even wear. :)
     
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  8. DanielB

    DanielB Noble Member

    Jan 13, 2019
    865
    393
    Abingdon, Oxfordshire
    Freck; thank you.

    I nice job to attend to when in isolation!
     
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