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center lock disc issue

bobbydigitalbobbydigital Posts: 254
edited September 2018 in MTB workshop & tech
I cannot get these rotors to line up, or shall I say I cannot get the caliper/pistons to operate centrally on the disc.

One of the pistons always touches the disc first and pushes it slightly.
Disc is RT 81 Ice tech and is brand new.
I have tried multiple brakes with different calipers but get the same results.

The disc is true.
Pistons on the calipers move equally off of the disc.
Currently using a m785 brake, tried with old style m395 which have br 477 calipers and tried with m615 calipers, all end up touching the disc slighty on one side before the other, any one ever had an issue with center locks?


  • CitizenLeeCitizenLee Posts: 2,227
    Have you done this?

    Loosen caliper bolts
    Apply brake
    Tighten bolts
    Release brake
    NukeProof Mega FR 2012
    Cube NuRoad 2018
    2015 Genesis CdF 10, 2014 Cube Hyde Race, 2012 NS Traffic, 2007 Specialized SX Trail, 2005 Specialized Demo 8
  • steve_sordysteve_sordy Posts: 2,381
    It works for me too.
  • I have tried that method many times but never find it lines up correctly, maybe that's just me but I have noticed a leak on the m785 caliper so not much use now. :cry:
  • kajjalkajjal Posts: 3,380
    What you are seeing is normal, unless it is very pronounced. Sometimes you need to set the calliper up by eye to compensate for this, assuming it is not faulty in some way.
  • No it isn't major, maybe 0.5mm off center so one side touches the pad ever so slighter sooner than the other.

    I found a m506 that lined up nicely but feels a bit spongy so might need a bleed, never had issues before, tempted to try my other wheelset which uses 6 bolt disc to see if it chances anything, the ice tech discs look a tad thicker.

    The m506 came off my 26" xc which had 6 bolt disc and it felt really solid, put on the center locks and it's not so great, seems a bit strange.
  • 02gf7402gf74 Posts: 1,168
    the ice tech discs look a tad thicker.

    I seem to remember that it is the case and need matching shimano callipers.

    Having said that, I have a pair of them, these are the earlier model without the fancy alloy cooling fins, and haven't noticed them being thicker. They are running with matching xt calliper.

    ....but it as long as the pistons move apart to let the disc in, it shouldn't matter as the hydraulic pistons are self adjusting.
  • Yeah I'm just a bit ocd about brakes, I like minimal level travel and sometimes find the m395 style levers feel better than the m785 style, I tend to pump the brake off of the caliper in order to reduce pad travel.
  • Yeah I'm just a bit ocd about brakes, I like minimal lever travel ..............

    Weird isn't it, how we are all different? :)

    I don't mind a bit of lever travel, as long as the lever goes hard at the end. I prefer to feel the brake start to engage almost as soon as I move the lever and then progressively get firmer and firmer. I haven't measured the travel, but just visualising it now, maybe an inch of travel (25mm) from fully off to fully on?

    My 11-year old grandson is the same (of course he is, I trained him and set up his bike!) But his mates nearly always go OTB when they test ride his bike. They complain "why are your brakes so fierce?" :lol:
  • caliper mounts may need facing OP. -wheel building and other stuff.
  • I am used to sporty motorcycles that have okay to good brakes so always go for the 10mm of travel if I can, Shimanos seem a bit hit and miss but I do always buy them used.


    It is difficult to move the caliper left and right on the I.S to Post adapter so could be an issue there, I think I have some new adapters somewhere but the fork was brand new, only done maybe 100 miles, Salsa Firestarter.

    Is there any known issues with air in the lever of the m506 levers?
    They are just not as solid as I would like, fully bled, burped with the funnel, does anyone ever do a bleed from top to bottom rather than shimanos bottom to top method?
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