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SLX brake issue thats got me confused!

mlbakermlbaker Posts: 77
edited July 2011 in MTB workshop & tech
Hi all,

I've got SLX discs, 180mm rotors and untill recently they've been great. Now though I having a strange problem in that they only work once I've got them hot.

I changed pads from sintered to organic and with fresh pads they are fine but after a while they only start working after some heating up.

from cold they are censored at best- can't endo or skid!

i've bleed them, roughed up the rotors slightly and swapped pads so can't figure it out.

if anyone has any ideas i'm interested! its starting to spoil my ride not being able to brake properly from the off. once 'warm' they are good.

i wonder if the rotors are worn? fluid is leaking onto the pad and then gets burned off after use?

Posts

  • nicklousenicklouse Posts: 81,520 Lives Here
    you need to look at the pads. before and after they start working correctly.

    also try cleaning the rotors before use.

    where do you keep the bike?
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • mlbakermlbaker Posts: 77
    in my flat so i don't think they are getting contaminated whilst storing the bike
  • nicklousenicklouse Posts: 81,520 Lives Here
    where in the flat? it is very possible they are getting a coat of grease from cooking? or any other mucky liquid.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • mlbakermlbaker Posts: 77
    not near anything greasy so i don't think its that.

    what should i look for on the pads? glazing over? i wonder if they could glaze on cooling?
  • nicklousenicklouse Posts: 81,520 Lives Here
    glazing it too much heat.

    try cleaning them before use.

    also are you wheels removed and refitted before each ride?

    if yes it will be the pads rebedding in to adjust to the slightly new wheel position.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • mlbakermlbaker Posts: 77
    i will try cleaning before use next time. i have some muc-off disc brake cleaner but some other forums suggest alcohol is better?

    i do remove the wheels quite regularly but i've never had any issues before with over brakes.

    what i really don't understand is that once hot they feel great, bedded in etc. but then i leave them overnight and they'll be censored in the morning!?
  • 1mancity21mancity2 Posts: 2,355
    Is it both brakes or just one?
    Finished, Check out my custom Giant Reign 2010
    Dirt Jumper Dmr Sidekick2
  • mlbakermlbaker Posts: 77
    BOTH NOW BUT ORIGINALLY JUST THE FRONT
  • mlbakermlbaker Posts: 77
    Another point is that when cold they make a lot of noise and don’t stop but as they warm they quiet down as the power/bite increases
  • nicklousenicklouse Posts: 81,520 Lives Here
    so have you tried cleaning the rotors?

    what pads?have you read the info in the FAQs?
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • mlbakermlbaker Posts: 77
    kevlar superstar at the minute. did it with sintered too
  • omegasomegas Posts: 970
    Is there any change in the lever position or compression between hot and cold?
  • mlbakermlbaker Posts: 77
    no they bite at the same point hot or cold
  • mlbakermlbaker Posts: 77
    Well by bite I mean contact the rotor at when cold and bite when warm. Its very much like the pads glaze of cooling or become contaminated and this takes heat to burn off.

    I’m considering sandblasting the rotors at work to see what happens then.
  • 1mancity21mancity2 Posts: 2,355
    Sandblasting your rotors will rip your pads to bits, get some isopropanol and clean them, try them if it works your rotors are getting contaminated somewere, no one spraying furniture polish near your bike or anything like that?
    Finished, Check out my custom Giant Reign 2010
    Dirt Jumper Dmr Sidekick2
  • 1mancity21mancity2 Posts: 2,355
    Just a thought, take out your pads and leave over night see if any fluid is leaking from the pistons.
    Finished, Check out my custom Giant Reign 2010
    Dirt Jumper Dmr Sidekick2
  • mlbakermlbaker Posts: 77
    cheers 1mancity2 will try that asap
  • 1mancity21mancity2 Posts: 2,355
    Don't press the levers while your pads are out or your piston will come out, and you will have to push them back before you can get your pads in.
    Finished, Check out my custom Giant Reign 2010
    Dirt Jumper Dmr Sidekick2
  • nicklousenicklouse Posts: 81,520 Lives Here
    will not work as the system is closed.

    apply pressure to the lever and hold does it creep towards the lever? yes you have a leak.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • nwmlargenwmlarge Posts: 863
    to clean the brakes use car brake cleaner it's like £4 a can does the same thing
  • nicklousenicklouse Posts: 81,520 Lives Here
    nwmlarge wrote:
    to clean the brakes use car brake cleaner it's like £4 a can does the same thing

    just make sure it does not have rust inhibitors. as they will kill your pads.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
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