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Rear brake probs

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by NovaCoder, Feb 7, 2005.

  1. Hi all,

    Went for a long ride yesterday and I now have a prob with my rear disc brake, these are the symptoms:

    1) Piston looks like it's sticking out
    2) Fluid level has dropped right down (last time I checked it was fine)
    3) Nasty scrapping noise everytime the brake is used (still works though).
    4) Red-hot disc with what looks like a coating of smeared brake pad or maybe the disc is just f**ked now :(

    So it's obviously rubbing which has heated up the disc, but why has the level suddenly dropped and why is the piston sticking out.....any ideas?

    It's always rubbed a tiny bit but it's been like that for the past year without any probs.
  2. I'm guessing that perhaps the brake pad and/or rotor was excessively worn down causing the piston to go out too far and not return properly, this would explain the drop in fluid and rubbing brake.
  3. So either the pad(s) is worn or the disc is worn....I hope it's not the disc :(

    I was using the rear a hell of a lot yesterday (big fangy down the mountains) so I guess that's what made it so hot.
  4. Pad is worn not the disc.
    You will have to change the pad asap before it does damage the disc.
    with the rear it is not as important to get it machined as the greater surface area the slightly "scratched" disc now has means better braking when the new pads bed in. (assuming you haven't buckeled the disc)
  5. It was nice and shiny before, now it looks like it passed through the center of the sun :eek:
  6. If a rippled rotor has a greater surface area and better braking then why do factory rotors and even race bikes still use a smooth, machined surface? :?
  7. Sounds to me more like the brake piston has seized. You'll have to pull the brake unit off the rotor, remove the pads, and see if you can push the piston back into the unit. If you can, ok .. new pads, refill fluid, bleed, and refill again. If you can't .. off to the mechanics for a brake rebuild or replacement.
  8. Cheers for the replies :)

    Looks like I'll need to get those latex gloves on tonight....
  9. Pads bed in quicker in a race situation with a smooth surface and assuming the tolarances that racers use they need to bed in quick.
    Pads in scratched disks will take longer to bed in but will still have a greater surface area to provide grip.
    (its also a cost factor)
    You'll find even in cars that if the rotors are only slightly scratched they will not machine them.
    Be interesting to see how many riders in here when they change their pads also get their discs machined.
  10. Nova coder, 1st off check your pad thickness. Some have a groove in them a couple of mm off the backing plate & others you just have to measure & check to specs. 2nd, check the caliper piston hasn't siezed -pretty unlikely as it happened all of a sudden. Lastly, pull the master cylinder apart & replace the seals as they are the only thing that could cause the brakes to stick -other than the piston corroding into the master cylinder bore -check for pitts & corrosion before re-assembly.
  11. Nearly forgot this one, on very rare occasions the rubber brake line can swell & constrict the return flow of brake fluid -usually only happens on quite old brake lines.
  12. Finally managed to get the rear caliper off tonight and found a distinct lack of pads...in fact only the backing plates remained. Piston went straight back in by hand, no probs there.

    All I need to do is fit some new pads and Bob is your uncle.

    My bad for letting the pads get so friggin worn!
  13. Might be a good idea to check the disc though...
    If needed, pick up the Verniers.
  14. Pete,

    Yep it is looking a little second-hand now (embarrassed). The funny thing is that I checked it a few rides ago and it looked ok.

    Message to all NetRiders, check the thickness of your pads regularly!
  15. Try the new pads first. ANY pulsing in the brake-pedal (wear sneakers/ thin-soles-stuff for a short test lap up the road for better feel) and the disc will need machining.
    Awesome Discs/ Ringwood.
  16. Don't get too excited about the way the disc looks, as long as it is still above minimum thickness and not warped the "secondhand" look will soon disappear with a few solid brake applications, you need to do this anyway to "bed" the pads. Hope you disc is Ok as they can be expensive.
  17. To bed in pads, you need to lots of short sharp brake applications. If you do a few solid brake applications from high speed you will glaze the pads and they wont work very well after that
  18. This should be done at least once a week as part of your, maintainance / safety checks

    Tyres / brakes / cables / lights / chain / loose fairing screws etc etc .
    I usually do all this just b4 'nicoles' wash or b4 any w/end ride .
    My bike is my only transport so by picking up any minor hickups when it happens, save heaps of time and $$$$ in the long run.

    just helping to keep the rubber side down