• This topic has 43 replies, 15 voices, and was last updated 2 years ago by nixie.
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  • New brake rotor, still rubbing…what's then?
  • dumbbot
    Member

    Afternoon,

    I’ve just replaced my front disc as it was rubbing i thought the disc was warped, so put on a brand new Sram centerline rotor so i would assume not dished(it appears not to be)…still rubbing in the same fashion, no amount of caliper alignment will fix the issue

    What does that mean?…wheel needs trueing?(almost brand new Planet shit ones so entirely possible/likely shit wheel build)

    Premier Icon molgrips
    Subscriber

    Rubbing in one spot as it turns?

    dumbbot
    Member

    Yeah, something like that..

    Edit: and new pads as well

    Gary_M
    Member

    Pistons not pushed right in when fitting new pads?

    dumbbot
    Member

    I did reset the pistons with a tyre lever when i put the new pads in, thing that gets me its its rubbing in almost exactly the same fashion as before.

    That vid that Qwerty posted is interesting, although i am loathed to start bending a new rotor…has anyone else had success with that technique?

    Gary_M
    Member

    I did reset the pistons with a tyre lever when i put the new pads in

    Did you check they are sitting flush though? Last time I changed the pads on my commuter I struggled to get the pistons to sit flush, even a mm out was causing rubbing. Liberal sprays of disc brake cleaner around the piston edge and pushing back got them flush.

    lazybike
    Member

    How much lever throw do you have? What I mean by that is when you pull the lever how soon do the pads engage?

    lazybike
    Member

    How much lever throw do you have? What I mean by that is when you pull the lever how soon do the pads engage?

    dumbbot
    Member

    they looked flush to me, but i could recheck that… Guide RSC brakes so adjustable bite point

    GavinT
    Member

    is it possible that the flange (snigger) on the hub isn’t quite true and when the bolts are done up it bends the disk? Seems a long shot but…

    lazybike
    Member

    I’ve no experience of the guide brakes, if the wheels not binding but just making that shh shh noise then I’d just ignore it!

    dumbbot
    Member

    just making that shh shh noise then I’d just ignore it!

    Just, JUST ignore it! 😯 😆 what kind of an animal are you….not possible, its driving me crazy.

    @GavT sounds plausible, but i’ve no way to check that.

    Could it be the wheel out of true though?…

    Gary_M
    Member

    then I’d just ignore it!

    That is utter madness.

    If the wheel is out of true it would be at the rim end, should still be trueish at the hub surely.

    dumbbot
    Member

    Impossible to ignore for me, needs fixing…i take your point about the rim not hub though.

    Could it be the wheel out of true though?…

    No, it’ll most likely be the rotor out of true. A lot are even from new.

    Premier Icon Speshpaul
    Subscriber

    New pads you, take them out, put some fine (220 min) wet and dry on a flat surface and knock the high spots off the friction material.

    lazybike
    Member

    😀 Ok then, Its unlikely to be the hub, find the point on the disc where its rubbing, shine a torch behind the caliper can you see one pad touching the disc and a gap on the other side, if you can, push on the disc with your thumbs to move the disc to the gap side, you can use a disc straightening tool or an adjustable spanner, but thumbs normally work.

    Premier Icon wwaswas
    Subscriber

    Put wheel in wheel jig and measure run out on the disc.

    Or just use a zip tie on the fork leg to check it.

    bigyinn
    Member

    I had a mavic crossride hub which had a similar issue, thought the disc was bent, but it turned out the hub flange was slightly out of true. The only way I could see to sort it out would be to machine it slightly in a lathe. I think I just swapped the hub out for another from a trashed wheel with a good hub.

    lazybike
    Member

    Alternatively…loosen caliper bolts, one and a half turns should do, spin the wheel and pull the brake lever, try that a few times, hold the brake on and tighten the caliper bolts.

    dumbbot
    Member

    Put wheel in wheel jig and measure run out on the disc.

    Or just use a zip tie on the fork leg to check it.

    Dont have a jig, but could you elaborate on what you mean?

    I’m really hoping its not the hub flange thing, because there nothing i can do if it on the wonk.

    dumbbot
    Member

    ahh **** it,..i’ll just bend the rotor, can’t be arsed with this.

    Premier Icon wwaswas
    Subscriber

    use an adjustable spanner to bend the rotor until it stops rubbing, basically. If you use a zip tie on the fork leg just touching the rotor as a reference it make sit easier.

    lazybike
    Member

    ahh **** it,..i’ll just bend the rotor, can’t be arsed with this.

    Easy tiger…over do it and you’ll be chasing that shh shh noise for hours..

    daern
    Member

    Dont have a jig, but could you elaborate on what you mean?

    “Run out” is where you measure the distortion from left to right on the rotor as the wheel turns in the jig. Honestly, turning the wheel and looking in the top of the caliper does much the same thing, if a little less accurately.

    The challenge is getting it straight again if it is wonky. My success rate isn’t great here and I’ve previously had to buy a new rotor if the old one is wonky.

    Premier Icon riklegge
    Subscriber

    ahh **** it,..i’ll just bend the rotor, can’t be arsed with this.
    Easy tiger…over do it and you’ll be chasing that shh shh noise for hours..

    “I thought I had it, but like an eejit I just kept tapping away…”

    dumbbot
    Member

    Well before i got all whoop ass on the rotor, i thought i clean the caliper and on further inspection my 4 pot sram brake, only 2(on opposing side) are in fact functioning…sticky pistons 🙄

    guess i need to bleed

    lazybike
    Member

    Lol…at least you found it!

    Gary_M
    Member

    sticky pistons

    Ahem 🙂

    Premier Icon molgrips
    Subscriber

    sticky pistons

    guess i need to bleed

    Think about it – why would bleeding help sticky pistons?

    If one side is stuck, it makes no difference if there are bubbles in there. You need to clean up that one side (use bike cleaner or brake fluid and a toothbrush) or simply free it up. What I do is push both pistons back then find a way to hold one piston whilst pulling the lever to force the other one to move. I can do it with a fat allen key through the caliper on my Hopes and hold it in place with my thumbs – bit of a faff to operate the lever like this but usually I can do it or ask a helper.

    Alternatively…loosen caliper bolts, one and a half turns should do, spin the wheel and pull the brake lever, try that a few times, hold the brake on and tighten the caliper bolts.

    That only works if both pistons are moving nicely and the caliper doesn’t move when you tighten the bolts up.

    dumbbot
    Member

    Ah didn’t read Molgrips post so unnecessary bleed did sweet FA. But great tip on how to get the piston free! 10mm allen, a tyre lever and some contortion forced the lazy piston into action.

    I’m still not happy they are advancing totally evenly, any secret squirrel tips on that?

    bigyinn
    Member

    Clean it with a cloth, then drip brake fluid around the sticky piston. Work piston in and out a few times, dripping a bit more fluid around the piston to clean and lubricate it.
    Its worth doing the same with the other 3 whilst you’re at it.
    Make sure you clean the fluid off the caliper afterwards mind!

    Premier Icon molgrips
    Subscriber

    any secret squirrel tips on that?

    Not really, unfortunately. Mine aren’t quite even but it doesn’t seem to make a lot of difference in use. I’ve heard bigyinn’s tip before about using brake fluid, that might work. Assuming they have brake fluid inside, of course.

    I replaced the seals in my Hopes which rejuvenated them, it was a faff though.

    lazybike
    Member

    That only works if both pistons are moving nicely and the caliper doesn’t move when you tighten the bolts up.

    That’s why you hold the brake on when tightening the bolts…but you’re right it won’t help with seized pistons

    Premier Icon molgrips
    Subscriber

    When you are holding the brake, you only have the stiffness of the disc to hold the caliper centred. And that is not much, it’s far less than the torque that tightening a bolt can exert on the caliper. I’m obsessive about brake rub, I’ve been into this in great detail 🙂

    Premier Icon benpinnick
    Subscriber

    Did you replace the bolts with the new disc by any chance?

    lazybike
    Member

    I probably see 5+ bikes a week that have brake rub…I’ll take all the advice or new tips I can get! 🙂

    dumbbot
    Member

    Did you replace the bolts with the new disc by any chance?

    No, I reused the old ones…should I have used the ones that came with the new rotor?

    Ive just trapped my finger in the rotor and mashed my finger nail…clumsy idiot that I am, raging

    Premier Icon benpinnick
    Subscriber

    No its actually the other way round. New ones often need running in then out again before fitting as they put so much threadlock on there the blue swarf can get behind the rotor and put it out of true.

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