Strange road disc problem

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  • Strange road disc problem
  • flattyre
    Member

    Anyone comes across this please? Any ideas?

    Shimano hydraulic disc on front of cx bike with QR.

    Position caliper in centre of rotor and after a quick ride is off-centre like the caliper has moved, with one pad rubbing. Bolts are as tight as I dare tighten them.

    Wheel is still in place throughout and happens every time.

    Premier Icon scotroutes
    Subscriber

    Unlikely the caliper is moving. Sounds more like you’re not fitting the front wheel straight in the dropouts before doing up the QR. Could be too much paint in the dropouts (or just dirt). It’s also worth checking that you don’t have a broken axle.

    Is it the pads sticking?

    Try moving them back with a screwdriver.

    Also as above check the wheel is centred.

    Sancho
    Member

    what hub is it, scotroutes seems right could be broken axle

    flattyre
    Member

    Thanks. I don’t think it’s any of those – clean, not broken and keeps happening if I leave wheel in and re-position caliper (i.e. wheel couldn’t keep moving??). Had Hope caliper before and was totally fine, but much weaker braking…

    flattyre
    Member

    It’s a cheap hub off Chinese carbon wheel – but seems fine and was perfect with previous brakes.

    Not just pads sticking as caliper is centered, then off centre

    mattsccm
    Member

    How do you do the QR up?
    I find that if I don’t do it with the weight on the wheels the positioning isn’t always exactly the same. Default now for me is loosen and retighten QR with bike on ground.
    Are the QR any good? Cheap external cam ones can move. Try with a decent internal cam one eg Shimano or Campag.

    Sancho
    Member

    is the fork collapsing where you tighten in the dropout?

    if its carbon it can collapse.

    flattyre
    Member

    QR is XT.

    I tighten QR with bike upside down but then ride it around a bit to make sure in place. Have had that a lot with QR forked mtb as I have to take the wheel off for car every time but with CX can leave the wheel on…so should just be set after one ride…

    Not sure what you mean by fork collapsing but setup is identical to previous brakes apart from it’s a different brake

    Premier Icon scotroutes
    Subscriber

    flattyre wrote:

    QR is XT.
    I tighten QR with bike upside down but then ride it around a bit to make sure in place.

    As above, it’s always best to have the wheel on the ground and some weight on it before tightening the QR

    Not sure what you mean by fork collapsing

    Is the dropout deforming under pressure? Not likely to happen with an alloy insert but could happen with a pure carbon dropout.

    Sancho
    Member

    Is the caliper tight on the fork?

    could the bolts be tightening against the inside of the thread and not nipping up the caliper, you could put a washer on the bolt to make sure, as if as you suggest the caliper is moving then it cant be tight enough.

    flattyre
    Member

    Dropout is allow insert but why would it deform differently before and after a ride?

    I push the wheel into dropouts as I tighten QR but it can move so will adopt that method from now on. Can’t see how it would keep moving over and over again though if I leave the wheel in place but keep re-centering the caliper…

    flattyre
    Member

    It’s pretty tight and more than Shimano min torque but worried about over tightening as have stripped thread on rockshox fork in the past.

    Will have a good look though to see if nipping up to caliper properly.

    I thought it must be caliper moving but then I can’t see why it would move it away from the center anyway? Maybe it’s pushing one piston with more force? Has some air in one side?

    Sancho
    Member

    are the pistons working evenly?

    if the caliper isnt moving then the pistons dont sound like they are working evenly, can you see if the pistons are showing the same amount?
    (might need to take the pads out)

    thecaptain
    Member

    Are you 100% sure that the wheel is still properly seated in the dropouts after you’ve ridden it? It could be a slipping QR problem (though I agree it’s hard to see how it can keep on moving further and further if you shift the calliper). Easy to check anyway, undo the QR while leaning on the front and the wheel will either clunk back into place or not.

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