Viewing 19 posts - 1 through 19 (of 19 total)
  • Brakes pulling to bar and losing power on long descents
  • Premier Icon alexh7878
    Free Member

    I recently bought some second hand SRAM guide RS’s and installed them on my trail/enduro bike. Whenever I am on a steep downhill decent which requires a lot of consistent braking, my front brake will lose all power allowing me to squeeze the lever most of the way to the bar, providing no braking force and also making a fog horn like sound.

    Under normal operation the brakes work fine and make no noise, it’s only when they are really hot that this occurs.

    Thinking maybe my rotors/pads were contaminated I replaced my pads and sanded and cleaned the rotor with IPA. However, the noise still persists. I am using sintered pads and 200 mm rotors.

    I had a LBS install the breaks, could it be that they didn’t bleed them properly? What is causing these symptoms?

    Thanks!

    Premier Icon jonba
    Free Member

    Contaminated pads/rotors would perform badly all the time. If anything heating them through use might help.

    Noise might just be a coincidence. Higher speed means more vibration and a louder noise.

    Sounds like contaminated brake fluid or air in the system.

    Premier Icon alexh7878
    Free Member

    Ok thanks. Time for a bleed then

    Premier Icon DickBarton
    Full Member

    A bleed will no doubt help as there could very well be air in the system. Have you tried the Race Kevlar pads from Uberbike (or Superstar)? Can you amend your braking style slightly to have less consistent dragging and more bigger grabs? That might help reduce the heat rise rate a wee bit.

    The following wont really help as you have answered them already but consistent braking can result in glazed pads and they won’t be helping with the slowing down, so you may need to roughen the pads up. What size of rotors are you using (you’ve already said 200mm)?

    Premier Icon bikerevivesheffield
    Full Member

    If you brought them to me I’d pop the pistons it and clean, then flush them through with new fluid, then bleed

    Premier Icon thols2
    Free Member

    If it was contaminated pads, you’d expect it to do it all the time. If it was air in the system, you’d expect it to do it all the time.

    It’s worth flushing them and refilling with DOT 5.1 fluid just to eliminate any questions about contaminated fluid. Buy a fresh bottle of fluid rather than using fluid from an already opened bottle.

    However, it sounds like you are overheating the pads. If you can fit a 220 mm rotor, that might help. If you can’t, a thicker, heavier rotor might help because there is more metal to absorb heat. A different brand or compound of pad might also help.

    If you are dragging the brakes all the way down the descent, the pads have no opportunity to cool, they just keep building up heat until the contact surface overheats and they lose friction. As DickBarton suggested, braking hard and then releasing the brakes for a few seconds can help because it allows air to circulate between the rotor and pad so the surface of the pads can cool off, whereas lightly dragging the brake all the time will just cook the pads.

    Premier Icon Scienceofficer
    Free Member

    Pad fade doesnt change lever reach though, although sometimes thats the perception as you squeeze harder in an effort to get it to work.

    This is either air in the system and/or
    Fluid contamination/degredation.

    IME you rarely get one without a bit of the other.

    Premier Icon chakaping
    Full Member

    I used to have those on an enduro bike and experienced the same issue when riding in the mountains.

    Honestly, I don’t think there was anything wrong with them, apart from not being up to the job.

    Premier Icon thols2
    Free Member

    I don’t think there was anything wrong with them, apart from not being up to the job.

    Yeah, SRAM do make an e-bike version with a different caliper for heavier duty use.

    Premier Icon Phil_H
    Full Member

    Ditch the sintered pads for organic/semi-metalic. I find anything else makes horrible noises on longer descents.
    If the levers are pulling to the bar at the bottom of the descent (i.e. Once the brakes heat up) but ok at the top or before you set off it could be the piston seals in the master cylinder need replacing.

    Premier Icon oikeith
    Full Member

    Yeah, SRAM do make an e-bike version with a different caliper for heavier duty use.

    Guide RE is the Ebike version, its the guide lever with the code caliper.

    OP, have a look at this video and see if it helps: https://www.youtube.com/watch?v=ys9bUOJ0qg0&list=WL&index=173&t=172s

    If not, and you do bleed, have a look at this video for an extra step to do: https://www.youtube.com/watch?v=WSjsFxrcfZw&list=WL&index=184

    Premier Icon toby
    Full Member

    Sounds to me like classsic symptoms of water in the fluid. Feel fine cold, but when really hot the water boils and steam bubbles act just like air bubbles.

    I’d start with a bleed making sure you’re using fresh fluid.

    Though I’d also look at practicing better braking technique (easier said then done when you don’t trust your brakes, of course). I say that as a bit of a brake dragger myself who’s often telling myself off mid-descent.

    Premier Icon flicker
    Full Member

    Pop the pistons out and clean/replace the seals then fresh fluid. Maybe brake pads after that depending on their condition.

    Premier Icon dyna-ti
    Free Member

    Dont just bleed, make sure you pump enough new fluid through to effectively replace whats in there.
    New pads, a bit of wet&dry cleaning of the rotors. Maybe as a last step fit new seals if you feel confident.

    Premier Icon greeny30
    Free Member

    Finned pads from uberbike and shimanos ice tech rotors could improve brake fade, I bought an extra big syringe for my epic bleed solutions kit to make flushing through with new brake fluid easier before bleeding as normal.

    Premier Icon pdw
    Free Member

    If you find that it’s pulling to the bar after releasing the brake and reapplying, then that suggests boiled (because it’s contaminated) brake fluid. New fluid needed.

    If you find that you’re having to pull harder and further to get the same braking effect during continuous braking (i.e. without releasing the lever) then that suggests pad fade due to overheated pads. Bigger discs or different pads needed.

    From the way you describe it, it sounds more like the latter.

    Premier Icon howsyourdad1
    Full Member

    Read the title  and thought…. “bet it is guides” . I replaced mine

    Premier Icon dannyh
    Full Member

    My guess would be air in the system. Dragging the brakes and/or using them a lot can pool the air in the system leading to brake fade.

    Premier Icon thols2
    Free Member

    My guess would be air in the system. Dragging the brakes and/or using them a lot can pool the air in the system leading to brake fade.

    This is not a real thing. It’s possible that dragging the brakes could cause the fluid to boil, but it won’t make any difference to air in the system. If you have a firm lever when they’re cold, it’s not air in the system. If there is air in the reservoir and you lay the bike down or turn it upside down, it can get into the master cylinder, but this has nothing to do with heat and it will often resolve itself with a few squeezed of the lever, which is the opposite of what’s happening here.

    The key symptom for me is the howling when they get hot. That’s not caused by brake fluid boiling or air in the system. It could be caused by the pads overheating though. Flushing and replacing the fluid is a sensible thing to do anyway, but changing the pad compound, bigger rotors, and not continually dragging the brakes are really the only things that will help if it is the pads glazing from heat.

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