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  1. #1
    curious noob
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    Dual Disc Brake Failure.

    I was riding in some very muddy conditions today and both of my mechanical disc brakes failed in the same way. First the rear brake (a shimano) stopped working. The lever was pulling all the way to the bar. Then the front brake (Avid bb5) suffered the same fate. After getting some mud off, I found the nonmoving pad, the one that you adjust with a knob on the bb5 and a hex bolt on the shimano had moved away from the rotor. Both brakes failed because the pad closer to the wheel had moved! It happened pretty fast too.

    I though disc brakes were supposed to be very reliable in mud and wet. What happened here and how do I prevent it? Mud was all over the brakes, crusted in the holes in the rotors and everything. Was I attacked by small ninjas concealed in the mud?
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  2. #2
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    "Was I attacked by small ninjas concealed in the mud?"

    Yes....ninjas called sand (as in sand paper) and they wore out your pads.

  3. #3
    curious noob
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    Quote Originally Posted by gmcttr
    "Was I attacked by small ninjas concealed in the mud?"

    Yes....ninjas called sand (as in sand paper) and they wore out your pads.
    That is possible, but I really don't think wear is the case. The ride was really short. Less than a half hour; we were immobilized by the mud and couldn't continue. Also, it only happened on one side, and it was the same side both times. All I can think of is some mechanism was lubricated by the mud, causing the pad adjuster to slide outward.

    When I clean things up, I'll check for pad wear though.
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  4. #4
    Nouveau Retrogrouch SuperModerator
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    Quote Originally Posted by drbroccoli
    That is possible, but I really don't think wear is the case. The ride was really short. Less than a half hour; we were immobilized by the mud and couldn't continue. Also, it only happened on one side, and it was the same side both times. All I can think of is some mechanism was lubricated by the mud, causing the pad adjuster to slide outward.

    When I clean things up, I'll check for pad wear though.
    I have had disc pads wear quickly enough on wet rides to require adjustment 3-4 times in 10 miles.
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  5. #5
    curious noob
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    Wow. I'll definitely be checking it then. I will have lost something like 1 mm of pad.

    EDIT: Now that I think of it, that still doesn't make sense. The brakes failed somewhat immediately. The brakes were fine when I used them once. Then next time, they pull all the way to the bar. There was no in between.
    Last edited by drbroccoli; 08-23-2010 at 10:41 PM.
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  6. #6
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    Geez I thought mechanical brakes were immune to failure??

  7. #7
    Nouveau Retrogrouch SuperModerator
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    Quote Originally Posted by jeffscott
    Geez I thought mechanical brakes were immune to failure??
    It is pad wear/"failure". Seen the same brand pads wear out in 3 rides in hydro discs.
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  8. #8
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    Quote Originally Posted by shiggy
    It is pad wear/"failure". Seen the same brand pads wear out in 3 rides in hydro discs.

    So let me get this straight...

    A single active piston brake will require more adjustment than a dual active piston brake, especially in muddy conditions.

    Further since the wear is placed on the two pads assymetrically the single active piston brake will wear out one of the pads faster.

    And adjustment would be considered part of maintance.

  9. #9
    thread killer
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    pics or it didn't happen.
    next time

    [QUOTE=spazzy] Might as well sell your bikes, E-riding is much more productive.

  10. #10
    ballbuster
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    Have you been adjusting your brakes...

    Quote Originally Posted by drbroccoli
    I was riding in some very muddy conditions today and both of my mechanical disc brakes failed in the same way. First the rear brake (a shimano) stopped working. The lever was pulling all the way to the bar. Then the front brake (Avid bb5) suffered the same fate. After getting some mud off, I found the nonmoving pad, the one that you adjust with a knob on the bb5 and a hex bolt on the shimano had moved away from the rotor. Both brakes failed because the pad closer to the wheel had moved! It happened pretty fast too.

    I though disc brakes were supposed to be very reliable in mud and wet. What happened here and how do I prevent it? Mud was all over the brakes, crusted in the holes in the rotors and everything. Was I attacked by small ninjas concealed in the mud?
    ... from the barrel adjuster at the lever? There's your failure point.

    Always adjust brakes form the pad adjusters at the caliper. Use the lever (or any other cable inline adjuster) just to take up the slack in the housing. What happens is the actuator arm on the caliper will creep up as the pads wear, and you adjust with the barrel adjuster. Eventually, the lever creeps up so far it hits the stop, and you can't pull the caliper closed anymore.

    Adjust the cable housing so that all the slack is taken out of the cable when the brake's actuator arm is all the way at rest. THEN adjust the pads to where your pad contact point is where you like it.

    Sounds to me like your pads wore quickly in the sand, and you ran out of room to adjust.

  11. #11
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    Quote Originally Posted by pimpbot
    ... from the barrel adjuster at the lever? There's your failure point.

    Always adjust brakes form the pad adjusters at the caliper. Use the lever (or any other cable inline adjuster) just to take up the slack in the housing. What happens is the actuator arm on the caliper will creep up as the pads wear, and you adjust with the barrel adjuster. Eventually, the lever creeps up so far it hits the stop, and you can't pull the caliper closed anymore.

    Adjust the cable housing so that all the slack is taken out of the cable when the brake's actuator arm is all the way at rest. THEN adjust the pads to where your pad contact point is where you like it.

    Sounds to me like your pads wore quickly in the sand, and you ran out of room to adjust.
    barrel adjuster is fine to use for small, quick wear adjustments during a ride, especially for a brake like the BB5 where adjusting the one side involves recentering the whole caliper. Then go back and do it the right way at home before the next ride

  12. #12
    curious noob
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    I never touched the lever barrel adjuster. The actuating pad hasn't changed it position noticeably. It's the caliper adjust that appears to have gone bad. I'm going to keep riding them and see if I can't think of anything.
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  13. #13
    Nouveau Retrogrouch SuperModerator
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    Quote Originally Posted by jeffscott
    So let me get this straight...

    A single active piston brake will require more adjustment than a dual active piston brake, especially in muddy conditions.

    Further since the wear is placed on the two pads assymetrically the single active piston brake will wear out one of the pads faster.

    And adjustment would be considered part of maintance.
    Mechanical disc brakes require manual pad wear adjustment. Always have. Not a single piston issue. Pad wear is fairly even when kept in adjustment (which is normal maintenance).
    Most hydros are self adjusting.

    The issue here is the pads wore very quickly in the mud, requiring mid-ride pad adjustment. I have had some Avid-branded pads (very inconsistent quality) that were basically water soluble. Wore clear to the backing plate (both pads) in 3 muddy rides. EBC Gold and Galfer pads in similar conditions are fine and usually require no more adjustment than in the dry.
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  14. #14
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    Quote Originally Posted by shiggy
    Mechanical disc brakes require manual pad wear adjustment. Always have. Not a single piston issue.
    Yes it is even the hydro's with a single piston need to be adjusted
    Pad wear is fairly even when kept in adjustment (which is normal maintenance).
    Most hydros are self adjusting.
    Even if the active side is self adjusting; they still need the inactive side to be adjusted

    The issue here is the pads wore very quickly in the mud, requiring mid-ride pad adjustment.
    Yup that is one issue
    I have had some Avid-branded pads (very inconsistent quality) that were basically water soluble. Wore clear to the backing plate (both pads) in 3 muddy rides. EBC Gold and Galfer pads in similar conditions are fine and usually require no more adjustment than in the dry.
    No question pads where out much quicker in mud and 3 rides can easily do in a set of pads.

    single piston brakes (mechanical or hydro) do not adjust for this as well as dual action hydros can and do...

    That is a significant disadvantage of single piston brakes either mechanical or hydraulic.

  15. #15
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    Quote Originally Posted by jeffscott
    No question pads where out much quicker in mud and 3 rides can easily do in a set of pads.

    single piston brakes (mechanical or hydro) do not adjust for this as well as dual action hydros can and do...

    That is a significant disadvantage of single piston brakes either mechanical or hydraulic.
    FWIW I don't think there are any currently produced single piston hydros. Even the cheap ones are dual piston. Last single piston I remember was the Hayes Sole

  16. #16
    curious noob
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    Alright, it does indeed look like pad wear. I took them out and was rather shocked and how much they have worn. It's strange how incredibly fast it happened, but it did.

    Thanks.
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  17. #17
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    Quote Originally Posted by gmcttr
    "Was I attacked by small ninjas concealed in the mud?"

    Yes....ninjas called sand (as in sand paper) and they wore out your pads.
    Thought so.

  18. #18
    Wrench
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    My BB5s pads wore out on a single dirty/wet ride. It was only 10 miles and they were gone.

  19. #19
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    My formula the ones would do about 20 miles in the mud before i need to replace the pads

  20. #20
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    Long distance set up

    Quote Originally Posted by boomn
    barrel adjuster is fine to use for small, quick wear adjustments during a ride, especially for a brake like the BB5 where adjusting the one side involves recentering the whole caliper. Then go back and do it the right way at home before the next ride
    For long multiday rides I started setting up the BB5's as follows:

    With the caliper mounting bolts loose and the caliper free to slide left and right and the brake actuating arm rotated back against the stop (moving pad fully withdrawn into the caliper body) with the cable pinch bolt loose enough to allow the cable to move freely:

    I run the fixed pad in with its adjuster until the pad engages the rotor. I then continue to move the fixed pad in until the rotor starts to contact the caliper body with the wheel spinning (as the fixed pad moves in the caliper body will move towards the wheel). I back the fixed pad out until the rotor just stops contacting the caliper body with the wheel spinning.

    I depress and lock the brake lever with velcro and tighten the caliper body mounting bolts to torque spec. I check to make sure that the caliper body does not strike the spokes or the rotor with the wheel spinning.

    With the moving pad now as mechanically close to the rolor as possible, I have a little more wear before the brake actuating lever reaches the top travel of its arch.

    I then spin the caliper barrel adjuster out 1/4 of its physical travel. I spin the brake lever barrel adjuster out 1/4 of its physical travel.

    I adjust the brake actuating arm until the movable pad is just touching the rotor with the wheel spinning, I ensure the brake cable is drawn tight and then torgue the cable pinch bolt to spec.

    I then screw the caliper barrel adjust in until the moveable pad is no longer touching the rotor as the wheel spins. If the caliper barrel adjust is full in with the pad still contacting the rotor, I spin the lever barrel adjust in until the pad is no longer touching the rotor with the wheel spinning.

    As the pads wear I adjust the stationary pad by rotating its adjust knob and the moving pad by adjusting the caliper barrel adjust first and then the lever barrel adjust.

    I have never had both the front brake and back brake pads wear the same, sometimes the moveable have worn more some times the stationary. As some point the brake actuating lever is going to reach the top of its arch due to pad wear and leverage at the brake is going to drop off rapidly. Before the brake actuating lever reaches the top of its arch I reverse the pads in the caliper.

    A new BB5 brake pad will be 153 to 155 thousandths thick including backing plate. At reversal one pad will normally be 130 to 140 thousandths the other 125 to 130 thousdanths. Avid recommends you replace pads at 118 thousdanths. After reversal - which in the field is a snap and requires no tools and just re-setting the caliper and lever barrel adjusters - I have ridden the pads down again until the actuating lever is near the top of its arch and the pads will be 120 to 122 thousdanths thick.

    On the current bike I have replaced 5 pairs of pads and have not had to adjust the caliper body location and the pads are always worn to 122-120 thousandths.

  21. #21
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    Quote Originally Posted by ZIT30/34
    For long multiday rides I started setting up the BB5's as follows...
    Reading that makes me very happy I have BB7s.

  22. #22
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    Quote Originally Posted by bad mechanic
    Reading that makes me very happy I have BB7s.

    Reading all of this makes me happier I have good quality Hydros

  23. #23
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    I never have these problems, I try to avoid riding in mud at all times, it's stupid. I learned my lesson in my 4x4 mud whomping around, it wrecks everything, on trucks, on bikes on cars. It gets into everything, it's abrasive, and it destroys your equipment.

  24. #24
    ...idios...
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    Quote Originally Posted by 006_007
    Reading all of this makes me happier I have good quality Hydros
    Beat me to it.
    .
    .


    What luck for rulers, that men do not think - Adolf Hitler

  25. #25
    curious noob
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    Quote Originally Posted by RandyBoy
    I never have these problems, I try to avoid riding in mud at all times, it's stupid. I learned my lesson in my 4x4 mud whomping around, it wrecks everything, on trucks, on bikes on cars. It gets into everything, it's abrasive, and it destroys your equipment.
    Yeah, I normally wouldn't either but I got caught in a rainstorm.
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