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Thread: whats the rub ?

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    whats the rub ?

    After adjusting brake pads in Avid BB7 calipers I will expierience brake drag while riding but not while the bike is on the repair stand. I had decided that the rub must be from the pad that moves not the fixed pad. I would typically stop and adjust the outer pad with poor results and then adjust the fixed pad until the rubbing stopped at which point I had bad brake feel at the lever but at least the #$@&% noise was gone.

    This weekend I took a more methodical and sane approach to the problem and to my surprise the noise was coming from the fixed pad rubbing the rotor. There is no contact between the rotor and pad on the stand, noise is most evident when sprinting or going uphill. I thought the bike must be flexing putting tension on the cable thereby moving the pad and causing contact. This is not case as it is the fixed pad that is making contact which does not make sense to me:
    the BB7 is mounted on the drop out which if it moved would move the brake with it.
    bike is a calfee dropouts are not slotted so wheel should not be slipping in the drop out
    hub.....Chris King
    rotor...Hope Moto/Tech V2

    I adjust the fixed pad 4 clicks and everything worked fine, no noise good feel at the lever>

    Anybody have an explanation?

  2. #2
    hors category TandemGeek's Avatar
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    When's the last time you serviced your Chris King hubs and re-adjusted the preload?

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    Quote Originally Posted by TandemGeek View Post
    When's the last time you serviced your Chris King hubs and re-adjusted the preload?
    Shop serviced in last fall about 3000 miles ago. I can not detect any play in the hub if I apply force at the rim by hand. I will have the shop take a look at it though.

  4. #4
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    I am going through the same thing on our '10 C'Dale's BB7's. I've got intermittent drag/light rub on both front and rear from time to time. I've followed Avid's manual to the letter and all is well for a while and then it comes back. Also tried inserting a spring on the cable to push back the caliper arm as recommended on this forum and again it helped for a while but the noise comes back. I will get the noise any where, flats or hills. Some time when it starts I just apply the brakes lightly for an instant and it will go away and sometimes it doesn't. I am also backing off the inside adjuster a couple of extra clicks (2 not 4) and that helps some as well.
    I am starting to believe that the problem is with the metal pad seperator (sp?) thingy. I wonder if it is just too weak and is loosing its ability to keep the pads in place when they are at rest.
    If you find a permanent solution please pass it on.
    I do love the stopping power of these things but the noise is driving me nuts.
    Bill J.

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    Tandem Vincitur Ritterview's Avatar
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    Quote Originally Posted by chichi View Post
    Do you think it has anything to do with wider-than-usual dual vented rotor, or the modifications to the BB7 to fit it?


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    hors category TandemGeek's Avatar
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    Quote Originally Posted by chichi View Post
    Shop serviced in last fall about 3000 miles ago. I can not detect any play in the hub if I apply force at the rim by hand. I will have the shop take a look at it though.
    What type of skewers are you using?

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    "Do you think it has anything to do with wider-than-usual dual vented rotor, or the modifications to the BB7 to fit it?"
    No the BB7 was wade wider by the same amount the rotor is wider than the stock unit

    "I am starting to believe that the problem is with the metal pad seperator (sp?) thingy. I wonder if it is just too weak and is loosing its ability to keep the pads in place when they are at rest."
    I have bent the spring to increase the pressure on the pads in the past, it has not resulted in any consistant improvement

    What type of skewers are you using?
    Salsa

    I stopped at the shop to check the hub for play and preload, it was checked by the mechanic last week. While you can not feel any play in the hub you can clearly see it, if you look where the rotor interfaces with the brake pads.

    Looks like a call to Chris King is in order.

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    Tandem Vincitur Ritterview's Avatar
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    Quote Originally Posted by chichi View Post
    I stopped at the shop to check the hub for play and preload, it was checked by the mechanic last week...
    Which shop? (I could use a recommendation). Sloughs?


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    Quote Originally Posted by Ritterview View Post
    Which shop? (I could use a recommendation). Sloughs?

    Slough's always does great work for me and they take a sincere interest in the problems unique to tandems.

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    Quote Originally Posted by chichi View Post
    Shop serviced in last fall about 3000 miles ago. I can not detect any play in the hub if I apply force at the rim by hand. I will have the shop take a look at it though.
    I spoke to Chris King customer service and it sounds like tightening of the preload or a hub rebuild is in order. They also cautioned me that using the correct lubricant will make a significant difference.

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    hors category TandemGeek's Avatar
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    Quote Originally Posted by chichi View Post
    I spoke to Chris King customer service and it sounds like tightening of the preload or a hub rebuild is in order. They also cautioned me that using the correct lubricant will make a significant difference.
    Sounds like a plan...

    And those are Salsa skewers with the stainless steel axles; yes?

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    Tandem Mountain Climber
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    same thing here, every once in a while.

    The flex is either the axle, the skewer or the bearings. The pedaling force is yanking on one side of the wheel, so it's up to the stiffness of the components mentioned to keep the hub straight.

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    PMK
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    It is probably bearing preload or flex as mentioned, one consideration too be aware of is the caliper aligning. Yes Avid gives initial pad settings for the caliper, I am talking about any tilt or off plane misalignment. First, loosen the QR, rock the wheel to settle it in the drop outs, without tilting the bike get the wheel tight. I normally need to reset the wheel every couple of hundred miles, not that it will fall out, it just moves slightly from where it was when the brakes were installed. Takes about 10 seconds.

    FWIW, when I install the calipers, I will align them with mount bolts backed off about 1/2 turn loose. Clamp the brake using the lever then while clamped snug the bolts until tight. Ride a bit up and down the street, giving some hard stops (maybe 10 or so) which help bed in the brakes, but also skive them flat. Then I go back and realign the caliper, again just barely loose, spin the wheel, grab some brake and hold it, snug them and see how the center and appear. This may take a few tries, and a bit of tinkering.

    We don't run BB7r's on the Co Mo, we run the mountain brakes with mountain levers. Very seldom do we get a rub. Most times it is the wheel has shifted almost nothing, or the road dust is built up and makes just a whisp of sound.

    PK
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    Tandem Vincitur Ritterview's Avatar
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    Quote Originally Posted by uspspro View Post
    same thing here, every once in a while.

    The flex is either the axle, the skewer or the bearings. The pedaling force is yanking on one side of the wheel, so it's up to the stiffness of the components mentioned to keep the hub straight.
    I haven't as yet gotten any of this rub, but my wheel should be vulnerable, as none of the components are rated tandem.

    DT 240 rear disc mountain bike hub
    KCNC 46 gram skewers
    Formula 220 rotor, 9 mm further out than 203 mm.






    Maybe the 135 mm as opposed to 145 mm OLD decreases the leverage?

    Perhaps the rest of the wheel (spokes, rim) contribute to the hub axle's resistance, as does the truss of of cantilever bridge?

    Maybe our feeble pedaling force provides insufficient yanking flex?

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    PMK
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    Quote Originally Posted by Ritterview View Post
    I haven't as yet gotten any of this rub, but my wheel should be vulnerable, as none of the components are rated tandem.

    DT 240 rear disc mountain bike hub
    KCNC 46 gram skewers
    Formula 220 rotor, 9 mm further out than 203 mm.






    Maybe the 135 mm as opposed to 145 mm OLD decreases the leverage?

    Perhaps the rest of the wheel (spokes, rim) contribute to the hub axle's resistance, as does the truss of of cantilever bridge?

    Maybe our feeble pedaling force provides insufficient yanking flex?

    I would not sell yourself short on pedal input...FWIW, those hubs run a 15mm diameter axle, supported almost to the dropout. For comparison, a typical DT tandem rear hub is a 10 mm axle. Also the DT's have no bearing adjustments or conical bearing preload collars. These hubs support the bearing 100% across both inner and outer races.

    The one problem you may have with a 240 is trashing the freehub body since it is aluminum.

    We destroyed the cassette splines on our 440 hub (large axle also) with an aluminum freehub. We sucked it up and went with steel as a replacement. Also this is on our full suspension ECDM which is not always spinning, yes sometimes we mash on that bike.

    PK
    2006 Co-Motion Roadster, flat bars, discs and carbon fibre fork, size 22 / 19
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    It would be interesting to find out how close teams are able to set pads to disc before intermittent rub becomes an issue. I will try to get a set of feeler gauges on mine this evening.

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    Quote Originally Posted by Ritterview View Post
    I haven't as yet gotten any of this rub, but my wheel should be vulnerable, as none of the components are rated tandem.

    DT 240 rear disc mountain bike hub
    KCNC 46 gram skewers
    Formula 220 rotor, 9 mm further out than 203 mm.






    Maybe the 135 mm as opposed to 145 mm OLD decreases the leverage?

    Perhaps the rest of the wheel (spokes, rim) contribute to the hub axle's resistance, as does the truss of of cantilever bridge?

    Maybe our feeble pedaling force provides insufficient yanking flex?
    Has the formula "floating rotor" eliminated heat induced warp?

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    Different problem than the op.

    Our stock Avid BB7 setup with G3 disc will rub after a very hard stop. This will go away after 1-2 miles and one light application of the brakes.

    I wonder if the return spring gets too hot and losses it's effectiveness. That and discs warping a bit due to heat build up.

  19. #19
    Tandem Vincitur Ritterview's Avatar
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    Quote Originally Posted by chichi View Post
    Has the formula "floating rotor" eliminated heat induced warp?
    We definitely have introduced the 2-piece, aluminum carrier, Formula 220 to some braking heat (and rapid coooling). But it has not warped. I don't know if the aluminum carrier helps, or whether we are just lucky.

  20. #20
    Senior Member Bent In El Paso's Avatar
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    Great thread. I have noticed my BB7 front brake "sings" once in a while when I get my weight over the front bars. After reading these threads, I think it is time to check the bearing preload.

    Thanks!
    Fred

    Behind every good captain is a great stoker!

    Co-Motion Speedster Co-Pilot

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    PMK
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    Quote Originally Posted by chichi View Post
    It would be interesting to find out how close teams are able to set pads to disc before intermittent rub becomes an issue. I will try to get a set of feeler gauges on mine this evening.
    TLAR, TSAR, TFAR, Done.

    If it stops it goes...

    PK
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  22. #22
    PMK
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    Quote Originally Posted by sine View Post
    Different problem than the op.

    Our stock Avid BB7 setup with G3 disc will rub after a very hard stop. This will go away after 1-2 miles and one light application of the brakes.

    I wonder if the return spring gets too hot and losses it's effectiveness. That and discs warping a bit due to heat build up.
    If the paint did not blister the spring will be fine. The disc may have warped slightly. You will know when the rub is bad, it loses that wispy sound.

    PK
    2006 Co-Motion Roadster, flat bars, discs and carbon fibre fork, size 22 / 19
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    And most important, someone special that enjoys them with me (except the KTM's)

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    Quote Originally Posted by PMK View Post
    TLAR, TSAR, TFAR, Done.

    PK

    ? That looks about right, That seems about right, That feels about right, ?

  24. #24
    PMK
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    Quote Originally Posted by chichi View Post
    ? That looks about right, That seems about right, That feels about right, ?
    That Sounds About Right, other two are good.
    2006 Co-Motion Roadster, flat bars, discs and carbon fibre fork, size 22 / 19
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  25. #25
    Eclecticaleliptic! Mainframeguy's Avatar
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    Quote Originally Posted by Ritterview View Post
    ...
    Maybe the 135 mm as opposed to 145 mm OLD decreases the leverage?
    ...
    Maybe our feeble pedaling force provides insufficient yanking flex?
    This was cool to read, now I feel better about my old C'dale with the 135 rear even though it is making a rear drum "challenging" to fit! Also I no longer see our relatively low torque as a completely negative thing! Having said that we did once manage to snap a chain! But that was a very OLD chain on a very OLD tandem!

    Still on rim brakes here so cannot comment on pad alignments, closeness, or noises, but it all sounds very swish!

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