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Disc brake question

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  • 05-11-2016 9:38pm
    #1
    Muckers
    Registered Users Posts: 504 ✭✭✭


    I'm having a problem after bleeding my hydraulic disc brakes and it's wrecking my head. Rear brake was simple and is operating fine. Not so with the front. I have rotor rub and have found that 1 of the pistons is not retracting after releasing the brake lever.

    My question is, what causes the piston to retract after releasing the brake lever. I understand that the pressure on the piston has ended once the lever is released. But what makes it retract backwards. Understanding this will hopefully help in solving my problem


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    #2
    dev100
    Registered Users Posts: 1,002 ✭✭✭dev100


    What brand are the brakes . Some brands are notorious


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    #3
    Muckers
    Registered Users Posts: 504 ✭✭✭Muckers


    dev100 wrote: »
    What brand are the brakes . Some brands are notorious

    Shimano BR-M445 with bo1s resin pads


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    #4
    C3PO
    Registered Users Posts: 3,763 ✭✭✭C3PO


    From what I understand there is a spring in the master cyclinder that retracts the lever which in turn retracts the pistons - the small external spring then pushes the pads away from the discs.
    In my experience (years of squealing MTB brakes!) it's very important to regularly clean the pistons with WD40 or similar to keep them retracting smoothly .... obviously being very careful to avoid getting any lubricant onto your pads!


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    #5
    Chuchote
    Closed Accounts Posts: 5,368 ✭✭✭Chuchote


    I was reading about how it's important to 'bed in' new disc brakes, but can't see any simple instructions for how to do this. Has anyone done it?


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    #6
    dev100
    Registered Users Posts: 1,002 ✭✭✭dev100


    Chuchote wrote:
    I was reading about how it's important to 'bed in' new disc brakes, but can't see any simple instructions for how to do this. Has anyone done it?

    Spin hard and pull the the breaks for a period of time and release and go again simple as that


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    #7
    Chuchote
    Closed Accounts Posts: 5,368 ✭✭✭Chuchote


    dev100 wrote: »
    Spin hard and pull the the breaks for a period of time and release and go again simple as that

    Turn the bike upside down and do this? The piece I read said to do it for around 10 minutes (but didn't have your helpful instructions - thanks!)


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    #8
    dev100
    Registered Users Posts: 1,002 ✭✭✭dev100


    No just Hop up on the bike and do it some brake systems don't like being turned up side down

    Basically if it's an mtb bike when you put new pads in just don't go mad doing fast down hill bits until the pads have bedded new . Just go on the flat and get them working and after a while you will find the bite getting stronger the more you use them


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    #9
    cython
    Registered Users Posts: 4,769 ✭✭✭cython


    These ones seem pretty clear and straightforward: http://www.bikeradar.com/gear/article/how-to-bed-in-disc-brake-pads-31337/


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    #10
    Chuchote
    Closed Accounts Posts: 5,368 ✭✭✭Chuchote


    Ah, thanks. Kilmashogue, so.


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    #11
    Muckers
    Registered Users Posts: 504 ✭✭✭Muckers


    C3PO wrote: »
    From what I understand there is a spring in the master cyclinder that retracts the lever which in turn retracts the pistons - the small external spring then pushes the pads away from the discs.
    In my experience (years of squealing MTB brakes!) it's very important to regularly clean the pistons with WD40 or similar to keep them retracting smoothly .... obviously being very careful to avoid getting any lubricant onto your pads!

    Thanks for that. The piston seems to be ok now after a bit of playing around with it. I'm left with a small bit of rotor rub. Is this any harm??


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    #12
    Chuchote
    Closed Accounts Posts: 5,368 ✭✭✭Chuchote


    YouTube, others will comment with advice; I know nothing ;)



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    #13
    arybvtcw0eolkf
    Closed Accounts Posts: 24,878 ✭✭✭✭arybvtcw0eolkf


    dev100 wrote: »
    No just Hop up on the bike and do it some brake systems don't like being turned up side down

    Basically if it's an mtb bike when you put new pads in just don't go mad doing fast down hill bits until the pads have bedded new . Just go on the flat and get them working and after a while you will find the bite getting stronger the more you use them

    Chu this is a more accurate description of how to 'bed in' brakes.

    Basically just ride your bike as usual but taking extra care for a few kms, you'll feel them bite properly when they're working.. Kinda like the feel you get when your bike is new, it really doesn't take too long or much effort.

    DON'T think you can just spin and hold the brakes extra long, depending on the material used in the pad you could glaze the pads (worse case).


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    #14
    C3PO
    Registered Users Posts: 3,763 ✭✭✭C3PO


    Muckers wrote: »
    Thanks for that. The piston seems to be ok now after a bit of playing around with it. I'm left with a small bit of rotor rub. Is this any harm??

    Probably no harm but would drive me mad!


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    #15
    arybvtcw0eolkf
    Closed Accounts Posts: 24,878 ✭✭✭✭arybvtcw0eolkf


    Muckers wrote: »
    Thanks for that. The piston seems to be ok now after a bit of playing around with it. I'm left with a small bit of rotor rub. Is this any harm??

    What kind of rub?.

    If the pistons are seizing, or binding then worse case scenario is they'll lock up the wheel when the tyres have low traction ~ ie icy or wet/greasy roads in the winter without you even touching the brake lever.

    It can also lead to premature pad wear, or another worse case 'do you have a warped disk?. (easy to check, using screw driver or similar hold it against the forks and the disk in such a way that it doesn't move.. Spin the wheel and if there's any oscillation in the disk/screw driver (high and low points on the disk) then you may have a warped rotator.


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