Disc's grinding?

Tommy Gun
Tommy Gun Posts: 6
edited September 2010 in MTB beginners
Hi All.

I'm still fairly new to all this, starting a few months ago after being roped into some team race. Been using a borrowed GT Aggressor which I gave back a few weeks ago. Decided to buy myself the new cube LTD Pro as a replacement. Anyway to the point...

Took it out for its first ride today and am a little concerned on a few points- I was hoping you can let me know whats what.

Firstly the bike seems to periodically make a grinding sound on the rear disc- I know they need to be broken in but is this right?

Also the breaks in general seem terrible, they need a real good squeeze to lock them up, and don't seem to make any difference until about 1/3 depressed. I checked with the guy in the shop who assured me they were bled- they're Shimano BR-M4451 hydr. discbrake (maybe the brakes are just rubbish?) Again I'm hoping this will improve over time.

With the brakes, how can I adjust the play in them. I would prefer it if they very sensitive- and only a small squeeze locked them out.

Thanks chaps!
Cube LTD Pro 2011

Comments

  • RevellRider
    RevellRider Posts: 1,794
    Is the 'grinding' a constant noise?

    The brakes don't have any free lever travel adjustment, that's the way Shimano have designed them to work. I'm sure someone will pop along with a tip on how to adjust the a ghetto way though.
    Alpha, Beta, Gamma, Epsilon.
  • x-isle
    x-isle Posts: 794
    When you say that they need a good squeeze, is the lever almost touching the handlebars when pulled enough to stop?

    If so, it sounds like they may need a bleed (get the shop to do it if you are not happy doing it yourself, remember that Shimano use their own organic fluid and not dot 4 or 5.1 fluid).

    If they are "hard" enough and not travelling almost all the way to the bars, it seems as though you may have contaminated pads/disks (it could be that they haven't bedded in yet, but I'm sure they should be).

    The griding noise could be dirt stuck in between the pad and disk and this could even be giving you the problems. I'd take the pads out and clean everything up and try again.
    Craig Rogers
  • Andy!
    Andy! Posts: 433
    check the caliper alignment by looking at the disc when you press the lever. if the disc moves then the caliper is not set right which may be a cause of your grinding.

    Not sure about the feel though.
    Merlin Malt 2
  • x-isle
    x-isle Posts: 794
    Andy! wrote:
    check the caliper alignment by looking at the disc when you press the lever. if the disc moves then the caliper is not set right which may be a cause of your grinding.

    Not sure about the feel though.

    Ooo yeah, that too, sorry forgot to mention that. It can also cause some dodgy lever feel too, so add it to the list to check.
    Craig Rogers
  • Andy!
    Andy! Posts: 433
    used to have it on my Hayes sole and then my Merlin when it came with the wrong adapter.
    Merlin Malt 2
  • nicklouse
    nicklouse Posts: 50,675
    a bleed is one of the last things that should be done.

    alignment and cleaning sound like the solution.

    BUT as it is a new bike it should really go back for sorting as it could well be poor set up.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • Tommy Gun
    Tommy Gun Posts: 6
    Thanks for all you help. I'll check the things you suggested and let you know the outcome.

    In answer to you questions the grining noise is not constant, only occasstionally at random times.

    The breaks don't touch the handlebars and are stop about 20mm from the grips, (although the right comes closer than the left?) But I get no response for the first 10mm at all, and then they don't feel responsive after that - to be honest they feel worse than the pads I had on my old GT.

    I would like to think the bike shop isn't too blame, they spent time making sure the forks were at the right pressure, and it was all set up right for me - I cant imagine they would go to all that trouble and then not make the effort with something like the brakes.

    I'm hoping the next ride will be better, and it just needed a few miles to get bedded in.

    Ill keep you posted!
    Cube LTD Pro 2011
  • Thewaylander
    Thewaylander Posts: 8,594
    well there is a certain amount of level travel that is the pads moving to contacting the rim, so about a cm of movement doesn't sound to far out to me..

    as for occassional grinding were you riding in mud? as get some quality grit int here and there is your grinding,and power most brakes come with organic pads,(hope i get this right) which aren't the best in the wet, and so good sintered pads will help once you have run the standards ones out :p

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