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Problem(s) with Avid BB7 Mechanical front brake

4.9K views 10 replies 9 participants last post by  Jayem  
#1 ·
Hi everyone!

I have a slight but annoying problem with my BB7 front brake. I have a Nishiki X-29 frame which has been rebuilt by different components. As can be seen from the pictures I have a Manitou Tower Pro fork.

As to the problems, I just recently replaced new original sintered Avid pads to the front (ridden less than 50 km after installation). Braking power is good, but they squeal quite a bit with - how should I best describe it - a prolonged braking with lesser but equal amount of force being applied to the brake lever. When more force is applied to the brake it feels as if the whole brake starts to vibrate, not violently but enough to notice that as if everything is not quite right with the brakes.

So there's the problem (1) of squealing with lesser force applied to the brake lever with prolonged braking and the problem (2) with the front brake starting to vibrate when more force is applied. The problem (3) is that after replacing the new pads the front brake drags or slows down all the time.

It should be mentioned, that I have the exact same brake setup in the rear (with 180 diameter rotor both in front and rear) and have absolutely zero problems there: no squealing, no dragging, no vibrating. Furthermore, the squealing is worse with the new pads.

I reckon that the vibration part of the problem has been more or less existent also with the old pads.

The dragging problem is new: I had some initial problems a few years ago with the old pads while they were still brand new to get the setup right. But now with the new pads, I have checked everything many times and it seems that no matter what I do they will still slow down and drag so that the wheel cannot travel freely. The bike is still rideable, that is, the dragging is not that bad, but of course it would be nice to have the setup right. I don't know if the pads require some "adapting" phase.

What caught my attention (pertaining, I guess, mostly to the vibration issue) the most is how the front pads (see the pictures) "come so much out" of the rotor, more so than in the rear brakes. It seems like the outermost part of the disc rotor is not at all touching to the pads while braking. This could maybe indicate that the whole setting is mounted incorrectly. However, I'm 100% sure that the pads are installed correctly. The only possibility in my view is that the mounting of the whole brake caliper is wrong, but if I'm not wholly mistaken, the mount I am using currently was the only option that was fitting (at least, that came along with the original Avid packaging) at all to the Manitou fork.

Thanks for the help and feedback guys!
 
#6 ·
Remove the pads, lightly sand, wipe down rotors with isopropyl alcohol. Back your inboard and out board adjusters out as far as they will go. Center your calipers by loosening up the fixing bolts, grab a fistful of lever and tighten them. Now turn your adjusters as close to the rotor as you like. The closer the pad to rotor the less lever throw you'll have. If I remember correctly one pad is stationary and the other pad forces the rotor into the other pad. I could be wrong, I had BB7's on an older bike and never had an issue, if adjusted correctly.
 
#7 ·
Remove the pads, lightly sand, wipe down rotors with isopropyl alcohol. Back your inboard and out board adjusters out as far as they will go. Center your calipers by loosening up the fixing bolts, grab a fistful of lever and tighten them. Now turn your adjusters as close to the rotor as you like. The closer the pad to rotor the less lever throw you'll have. If I remember correctly one pad is stationary and the other pad forces the rotor into the other pad. I could be wrong, I had BB7's on an older bike and never had an issue, if adjusted correctly.
I agree except for the bold statements above.

OP, take the pads out, do a light sand with 220 grit, wipe the pads and rotors with rubbing alcohol.

Then look up youtube videos on how in to install/adjust BB7 brakes. Here is a good once for the road brakes, but the mountain are very similar:


You need to make sure that your calipers are aligned and your inboard and outboard pads are set correctly. After they are set up properly, make sure you bed in the brakes. Start with a couple moderate stops without letting the bike come to a stop. Then do several hard stops without letting the wheels lock up or come to a stop. That should help.

As leeboh said, the vibration in the front could be from loose items or it could just be the flex in the fork.
 
#8 ·
Sorry for my delayed response! I have had many things going on during past few days.

Thanks for all the advice/feedback guys! I hope I have the time this weekend to try to get this problem(s) sorted out.

As an initial response:

(1) I have multiple times cleaned both the rotor and the pads with various brake cleaners = no help (well, maybe the squealing may go away for a little while, but no long-term help). No sanding of the pads has been done, however.

(2) When installing the new pads adjustments were made to compensate the new pads' thickness (the adjustments, as I write, are "maxed out", so no further adjustments cannot be even made).

(3) to ElwoodT: I'm not actually 100% sure about the rotor spec: The rotor itself has a text "180" as well as the original AVID BB7_mtn package "12A DB BB7 MTB FR/RR 180 IS 180G2CS". On the other hand, the original instructions that came along indicate, for example, in the different bracket section, i.e. "Make sure you have the right brackets" that the rotor sizes are "160"; "185"; "203".

(4) The vibration issue is, of course, possibly as a result of "loose items", or other issues. However, all the mentioned stuff, such as head set, wheel bearings and qr skewer were brand new when I firstly installed the brakes. So if there is no wrong installation done or faulty items concerned I think the best explanation is "flex in the fork". (I can offer further details of the components if needed.)

Thank guys, once again!
 
#10 ·
Remove the pads and file the sharp edges off the leading and trailing edges of the friction material.

Refit, applying a small smear of copper grease to back of the pads.

With the pads in their rest positions, undo the caliper mounting bolts and visually center the rotor between the pads.
 
#11 ·
The problem is a resonant frequency that is allowed to propagate. This is due to the mass of the caliper, pads, and what they attach to. What happens is when you bake, the pads are vibrating back and forth and this is magnified. There's no sure-shot solution unfortunately. It has to do with the harmonics. Somehow you have to change them. On the earlier camaro SS 2010 models with the brembo brakes, they added "roller skate" weights to the pads for this exact issue. In other applications, they'll sometimes add stick-on weights to the caliper.

I've had this issue with Avid brakes before. Sometimes it goes away, sometimes it does not. Changing the rotor for a different style is one possible solution, but a total solution might require changing the caliper or the fork. You can try to play around with the pad angle, and so on. Lots of things "might" work, but that's the nature of this issue.