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  1. #1
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    Free Avid BB5 to BB7 conversion?

    I've been tinkering around with my BB5's for a day now, and I found an interesting knob on the outboard side. If you take the protective red "Avid BB5" cover from the brake arm side, there's a black knob on there. There's about 16 cuts around the nut, and it's smooth at the center.

    I've tried to spin it with pliers/the protective cover (the shape of the nut is engraved in the plastic) to no avail. Could this be the same BB7 adjustment knob, just cleverly concealed? If both models of brakes were identical in assembly and one is just missing a knob...

    Anyone familiar with what this may be? I'm already thinking it may just be the break arm screw =/

    ---

    As a side note, can you sidestep the lack of an outboard adjustment know with several pieces of paper tucked behind the outboard brake pad?

  2. #2
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    I am thinking that it is just the bolt for the arm pivot.

  3. #3
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    Quote Originally Posted by aridese
    ...As a side note, can you sidestep the lack of an outboard adjustment know with several pieces of paper tucked behind the outboard brake pad?
    Not a good idea.
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  4. #4
    Nouveau Retrogrouch SuperModerator
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    Quote Originally Posted by aridese
    I've been tinkering around with my BB5's for a day now, and I found an interesting knob on the outboard side. If you take the protective red "Avid BB5" cover from the brake arm side, there's a black knob on there. There's about 16 cuts around the nut, and it's smooth at the center.

    I've tried to spin it with pliers/the protective cover (the shape of the nut is engraved in the plastic) to no avail. Could this be the same BB7 adjustment knob, just cleverly concealed? If both models of brakes were identical in assembly and one is just missing a knob...

    Anyone familiar with what this may be? I'm already thinking it may just be the break arm screw =/
    ...
    No. The BB7 pad adjuster (foot bolt) is a flat blade in the middle of the hollow bolt in the center of the caliper. The red knob slots over this blade.

    If you break the arm screw you should fix it.
    mtbtires.com
    The trouble with common sense is it is no longer common

  5. #5
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    Quote Originally Posted by shiggy
    Not a good idea.
    Why not?

  6. #6
    Meh.
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    Why do you need to shim out the outboard pad? You can just adjust the cable tension to push the outboard pad in or out. Less cable tension, pad further, more cable tension, pad closer. You can use the anchor bolt at the caliper or the barrel adjusters at your lever. In addition, BB5 and BB7 use different pads, and yes, that probably is just a nut to hold the arm on.

  7. #7
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    Increasing cable tension gives you less modulation. You sacrifice that same brake arm travel you'd be missing if you didn't increase the tension in the first place.

  8. #8
    Meh.
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    Dialing the pad in decreases lever travel as well. Think about it. All you're doing is decreasing the distance that the pad has to be pushed. If the pad has to travel less distance, less cable has to be pulled.

    The inboard pad position can be changed to affect modulation. If the pad is further from the rotor, the rotor needs to be pushed further before hitting the pad.

    By the way... Gorilla gluing studs into a fork? You could have at least gone the route of JB Weld...

  9. #9
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    It's not just touching/not touching, there's also the force applied to the rotor by the pads.

    If you have 3mm of space between the outboard pad and the rotor, then the brake arm has to travel those 3mm before it even considers slowing the wheel down. If you increase tension, then you only have 40% of brake arm travel ('modulation') to play around with. When you're increasing tension, you're just moving the brake arm closer and throwing out the modulation benefits of having it in its resting position. If you dial it in, then those 3mm are discarded, and you have 100% of brake arm travel to push on the pad.

    What you said is true if you're only concerned about if the brake is on or off, reducing brake arm travel DOES cut everything in between. Braking power might even be reduced -- those 60% that the arm COULD travel could have pushed the further even harder onto the disk.

    The inboard pad adjustment certainly plays a role in modulation, but it should be dialed in as close as it can be without rubbing. The outboard side has tenfold more effect if the inboard is dialed in properly.

  10. #10
    Meh.
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    You're over thinking it a bit.

    Yes, what you're saying is true to an extent, but for the sake of practibility, it doesn't make a difference. Your won't be able to use the end travel of the brake arm, because it will never pull that far. The amount of pull will be same, regardless of where the pull actually is. If you dial the pad in, the pull will be the first 3mm. If you increase the cable tension, the pull will be the middle 3mm. You are not going to compress the pads (again for the sake of practiblity).

  11. #11
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    Maybe it's placebo, but I really notice the difference depending on speed/mass. If the only difference between BB5 and BB7 was cable tension, I don't know why Avid would have different models.

    Different strokes for different folks...

  12. #12
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    The way I see it, you are getting the same amount of pull either way, just the pull is at different parts of the arm's travel.

    It's ease of adjustment. The BB5 uses a different pad. Cost of production is different, the BB5 is a lower cost alternative.

    Why bother having the J5 and the J7 and the JCarbon? They're all the exact same. J7 has a knob over the J5, JCarbon has a carbon fiber blade and some Ti bits over the J7.

    Why bother having multiple models of the same fork?

  13. #13
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    You're getting the same pull at the levers, yes. But the brake arm travels MUCH LESS for that same amount of pull. It's like moving 20mm of arm for 3mm of brake pad, instead of 10mm for those same 3mm. The pad may stop the wheel at parking lot speeds, but any faster and you'll need to "push" the brake pad harder in. You'll increase cable tension so you can stop when you're going fast, but you're losing the modulation at parking lot speeds.

    As for the BB5, I really can't see Avid saving more than a dollar as opposed to the BB7 (assuming they cost ~5$ to manufacture). But it's not "ease of adjustment", it's a completely different adjustment system. On the BB5 you need to realign the caliper to compensate for outboard wear (I still think cable tension is a Bad Idea), on the BB7 you turn a knob.

  14. #14
    Meh.
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    Yes... it pretty much is ease of adjustment... And a dollar is a dollar. Every bit helps when it comes to meeting price points.

    Okay, now I understand what you're saying about the pull. I still don't completely agree. But whatever floats your boat.

    If the brake arm has to travel more, so does the lever.

  15. #15
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    Quote Originally Posted by aridese
    If you have 3mm of space between the outboard pad and the rotor, then the brake arm has to travel those 3mm before it even considers slowing the wheel down. If you increase tension, then you only have 40% of brake arm travel ('modulation') to play around with. When you're increasing tension, you're just moving the brake arm closer and throwing out the modulation benefits of having it in its resting position. If you dial it in, then those 3mm are discarded, and you have 100% of brake arm travel to push on the pad.

    What you said is true if you're only concerned about if the brake is on or off, reducing brake arm travel DOES cut everything in between. Braking power might even be reduced -- those 60% that the arm COULD travel could have pushed the further even harder onto the disk.

    The inboard pad adjustment certainly plays a role in modulation, but it should be dialed in as close as it can be without rubbing. The outboard side has tenfold more effect if the inboard is dialed in properly.
    Aridese, a couple of things.

    First, please stop using the term "cable tension." It's incorrect and misleading. Adjusting the barrel adjuster affects cable length, or more technically, housing length. Tension does not increase or decrease. All that happens is the caliper arm moves.

    If you want to adjust tension, you can adjust the return spring on the Avid caliper. That's the only way you'll affect it.

    Secondly, approach this with the assumption that the caliper arm always has more throw than the brake lever has the ability to actuate. That is the assumption that Avid made in designing this piss-poor excuse for a pad wear adjustment.

    Your typical Avid Speed Dial lever has the ability to pull between 20 and 26mm of cable in one squeeze of the levers. I haven't measured, but in working with these lousy brakes, I will guess that it would take around 35 to 40mm of cable pull before the lever bottoms out on a hard stop (not the rotor).

    So it doesn't really matter if the 20mm plus of lever squeeze is actuating the first 20mm of caliper arm or 10 through 30 or 20 through 40, the point is that is displaces the outboard pad approximately the same amount towards the rotor each and every time.

    And lastly, this has nothing to do with modulation. Modulation is adjusted by inboard pad spacing (which affects how far the outboard pad must deflect the rotor before it makes contact with the inboard pad -- less gap = "less modulation" / more gap "more"). And Modulation is affected by the Speed Dial adjustment, which affects how much cable is pulled with each lever squeeze.

    Adjusting the barrel adjuster has nothing to do with either: it does not move the inboard pad, and it does affect the ratio of cable pulled to lever squeezed.
    speedub.nate
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