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Brakes - lack thereof.

HaloricHaloric Posts: 12
edited September 2014 in MTB workshop & tech
It's a long story - I'll try to be brief !

I have a one year old boardman cx, and I've never been happy with the BB5 brakes. When I got it it was very badly setup with almost no stopping power, after some googling and video watching, I learned all there was to know about BB5 and got them setup better - but still not impressive. I'm a heavy rider, so maybe thats the best I'll get.

I gradually just became more and more unimpressed, cleaned them (with the right stuff), replaced the pads a few times, even took them apart down to the ball bearings when they got crunchy, greased the bits that needs grease and made sure nothing else came in contact, in the end I tried an LBS (a proper one) and was declared as good as they will get.

More googling, decided to try BB7, bought some used but as new from ebay, got new pads - result was better but still not impressive - I want to at least be able to lock the back wheel up on tarmac if I want to - with what I have I can't no matter how hard - its just a progressive stop, with no final bite point, and on steep off road I just can't stop. I have avid elixir on a couple of other bikes - a hybrid and a recumbent tandem that is twice the weight that will stop sharper than my cx.

The only thing I have not replaced is the rotors and the cables - so bought some Shimano SM-RT86 as a replacement for the stock Avid G2 - maybe the rotors are too badly marked (LBS says no - but getting desperate).

These rotors don't fit properly - they have a centre (plastic?) black section that is affixed close to the edge of the rotor, and on the inside of the rotor this plastic mounting just fouls the edge of the pad - the one that is slightly bent away from the rotor. The instructions say there is an outer fixing plate, which there isn't, but that would not help anyway.

As a result every 72 degrees (there are 5 'arms' on the center mounting) there is contact with the outwardly bent arm of the pad sticking out of the caliper. I might be able to get rid of this by adding a washer to the brake mounting bolts, lifting the whole calliper up a couple of mills, but that might move some of the pad away from contact with the outer edge of the rotor, making it sit high on the rotor, which I would prefer to avoid. I tried both rotors on my front wheel whilst trying to work out what the problem was - so they are both slightly marked now where the plastic has been worn by the edge of the pads 'arm' as I scratched my head looking at it.

The pads are labelled L and R, and the 'arm' of the R one is slightly bent - presumably to give extra clearance to the inside edge of the rotor. They are avid pads.

I can't adjust this away by moving the calliper using the standard mechanisms - its in the right place and aligned, its just that there is not enough clearance radially between the pad 'arm' and the way the rotor is manufactured.

I can probably try to file these arms down a few mills also - a bit vexing, should not need to do that.

The question is - should this rotor just fit as is or have I bought the wrong things for my BB7's ? I don't fancy my chances getting my money back unless I can show a common problem with this model of rotor.

Thanks for any advice

Posts

  • Ah - bit more googling and I am not alone in this discovery - also looks like these rotors were not the best choice for my BB7's due to other issues as well. Even more vexing.

    http://forums.mtbr.com/brake-time/avid- ... 70470.html
  • The RookieThe Rookie Posts: 27,756
    When my son had BB5's they were excellent, right up there with mid range hydraulics.

    Correct adjustment is critical though, and you can't clean a contaminated pad you have to replace it.

    Personally I'd start by putting on a reasonable pair of conventional discs and new pads, setting it all up. You can strip, clean and regrease the callipers internals but I doubt it's needed.
  • OuijaOuija Posts: 1,386
    Had the same problem with some BB5's and Hope rotors. They really aren't designed for mechanicals with static pads unless you raise the caliper up and lose performance thereby. Through the rotors on a spare mountain bike with clarks mechanicals on (which didn't fowl with the rivet that connects the inner piece of the rotor to the outer ring). But in the end i ditched those rotors and brakes and slapped some cheap Chinese BB5 clones on with conventional rotors which are doing a far better job than any BB5's i've owned (still got em on two bikes). At £14 they're disposable and i can lock up the wheels anytime. Even thinking of slapping some on my other two BB5 bikes. Wouldn't replace my BB7's though, as i've always had excellent results with them (though a lot of it is down to how you cable the bike and how you setup the calipers).
  • With the brakes on the CX I have had some sucess with bending the the arms of the spring that pushes the pads apart.
    As it comes the spring is 'V' shaped and seems to angle the pads somewhat meaning that one edge of the pad is stating to rub well before the rest and generally the cables are a bit slack. If you bend the 'V' open a bit more and then bend the arms in a bit making them start wider, but more parallel you can get them to start much closer to the rotor
  • The Rookie wrote:
    When my son had BB5's they were excellent, right up there with mid range hydraulics.

    Correct adjustment is critical though, and you can't clean a contaminated pad you have to replace it.

    Personally I'd start by putting on a reasonable pair of conventional discs and new pads, setting it all up. You can strip, clean and regrease the callipers internals but I doubt it's needed.

    re: stripping - had to do that, but only one one, it was full of dirt and not moving smoothly at all.

    re: new pads - absolutely, all new.

    re: new discs - thats what I thought I was doing with the shimanos - turns out they are not as regular as I thought. I have shaved off the arms as much as I dare - to the point where I am concerned about the reliablilty of it attaching to the outer rotor, so now I'm looking for new rotors - a pair of new G2's are nearly as much on amazon as a full set of bb7 calipers (mountain version) including G2's !
  • With the brakes on the CX I have had some sucess with bending the the arms of the spring that pushes the pads apart.
    As it comes the spring is 'V' shaped and seems to angle the pads somewhat meaning that one edge of the pad is stating to rub well before the rest and generally the cables are a bit slack. If you bend the 'V' open a bit more and then bend the arms in a bit making them start wider, but more parallel you can get them to start much closer to the rotor

    Yes - although the dragging is not a problem yet, I dream of that being my only problem. Before I took the calipers apart I saw many people complaining about this slight angle, and saying it was giving them uneven wear.

    Once I took it apart I realised that the pad is pushed from a bearing in the centre - the angle at which the pad hangs when it is not being used is irrelevant to the actual angle when it is being pushed - the centre bearing will cause it to immediately align with the rotor once they come under force - as far as I can see.

    Obviously there will be some wear if there is minor contact when its not in use, but I have not seen that.
  • The RookieThe Rookie Posts: 27,756
    Haloric wrote:
    The Rookie wrote:
    When my son had BB5's they were excellent, right up there with mid range hydraulics.

    Correct adjustment is critical though, and you can't clean a contaminated pad you have to replace it.

    Personally I'd start by putting on a reasonable pair of conventional discs and new pads, setting it all up. You can strip, clean and regrease the callipers internals but I doubt it's needed.

    re: stripping - had to do that, but only one one, it was full of dirt and not moving smoothly at all.

    re: new pads - absolutely, all new.

    re: new discs - thats what I thought I was doing with the shimanos - turns out they are not as regular as I thought. I have shaved off the arms as much as I dare - to the point where I am concerned about the reliablilty of it attaching to the outer rotor, so now I'm looking for new rotors - a pair of new G2's are nearly as much on amazon as a full set of bb7 calipers (mountain version) including G2's !
    Have a pair of G2CS that came off a bike (running BB5's that would go on the front wheel with 2 finger braking), bit tatty but worked perfectly, yours for £10 delivered.
  • The Rookie wrote:
    Have a pair of G2CS that came off a bike (running BB5's that would go on the front wheel with 2 finger braking), bit tatty but worked perfectly, yours for £10 delivered.

    Thanks for the offer, I have some similar that I can see no problem with, but I'm going for new/unused for piece of mind just to be clear that its not the rotors fault, until I get to the bottom of it.
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