Bicycle Mechanics - BB7 Install trouble

I'm adding disc brakes to my xtracycle, and I've purchased BB7s. In order for me to get the brake not to rub, the gap is so wide that the braking force is pretty much only good for slowing, not for stopping. I've looked online and followed the suggestions. I can get the gap spacing correct, and then I adjust the pads per the instructions, but then when I turn the wheel there is considerable rub. I think I'm just not getting the caliper aligned correctly. Can anyone give me some pointers on how to do this correctly?

Install with mtn levers (basic, no name ones), 203mm rotor 160 mm caliper adapter (per xtracycle's instructions). BB7 Mtn caliper.

-I set up some BB7s for the first time this Winter and was surprised how easy it was. It did strike me that the alignment proceedure (locking down the pads and then tightening down the mounting bolts) could easily go awry. Even as I was doing it, I was thinking about a plan-B of putting a little dab of grease on the various concave/convex washers to be sure they would slip into alignment easily.

-In looking on-line (BF, and otherwise), it seems that people have found the mounting bracket on their frames to be off by a small amount sometimes. If so, the brackets need to be refaced to get them true.

A couple of diagnostic questions: Do the brakes rub all the way around the disc? Or just in spots? And also, can you tell if the disc is lined up square with respect to the stationary pad? Or is it at too much of an angle?

jim

I take it it's just the pads rubbing on the sides of the pads (not familiar with that adapter on extracycle stuff, hopefully it's not a caliper height issue in relation to the outer edge of the rotor). Is it just a rotor out of true? Did you follow Avid's instructions to the letter? Particularly being careful when snugging up the caliper to the rotor and then tightening it down incrementally? When you dial out the pads after tightening the caliper, is it leaning towards the inboard or outboard pad or do the pads back off equally? Sometimes you have to make sure the gap is equal on the top and bottom of the rotor, and not binding a bit when you're tightening the pads to the rotor. Do the mount tabs on the extracycle look straight? Do they need facing?

-I set up some BB7s for the first time this Winter and was surprised how easy it was. It did strike me that the alignment proceedure (locking down the pads and then tightening down the mounting bolts) could easily go awry. Even as I was doing it, I was thinking about a plan-B of putting a little dab of grease on the various concave/convex washers to be sure they would slip into alignment easily.

-In looking on-line (BF, and otherwise), it seems that people have found the mounting bracket on their frames to be off by a small amount sometimes. If so, the brackets need to be refaced to get them true.

A couple of diagnostic questions: Do the brakes rub all the way around the disc? Or just in spots? And also, can you tell if the disc is lined up square with respect to the stationary pad? Or is it at too much of an angle?

jim
The real beauty of the Avid mounting system is that a slight missalignment of the mounting bracket can be easily compensated for without refacing. There is nothing easier to set up.

The real beauty of the Avid mounting system is that a slight missalignment of the mounting bracket can be easily compensated for without refacing. There is nothing easier to set up.

I agree. Its slick. But, I have heard some people here say that their brackets were enough out of line that refacing was needed.

jim

Which model year of bb7? IIRC, older models had one pad stationary and one pad moved. Recent models have both pads move, and each model has a slightly different install technique.

I had this problem when I was first attempting to adjust mine as well. It seemed like I had to back the pads off quite a bit more than Avid's instructions claimed.

First, after you adjust the pads out, give the brake lever a couple of good squeezes to set the pads in place. I found that while the pads would sometimes rub right after an adjustment, actuating the brakes a few times would alleviate some of the rotor rub.

Second, and I'm not sure why it worked out this way, but I had an issue with a bad vibration using the BB7's on a cyclocross frame with a carbon fork. I resolved the vibration by increasing the torque on the rotor bolts. I also readjusted my caliper at the same time and found that with the higher torque, I only had to back off the outside pad by the recommended 3 clicks to get clearance whereas before it was more like 6 clicks. Now, obviously this could have had something to do with my previous set up not being perfect too but it sure seemed like a strange coincidence.

BTW, if you search for my thread about the rotor torque and vibration issue, you'll find that Avid stands by their recommendation etched into the rotor (6.2 N*m) even though the manual says 9-10 N*m. They claim the manual torque is a misprint but I had the vibration using 6.2 and didn't after upping it to 9.5. YMMV.

Which model year of bb7? IIRC, older models had one pad stationary and one pad moved. Recent models have both pads move, and each model has a slightly different install technique.

Not sure what you're thinking about but the BB7 (formerly BBDB) is virtually the same since inception, still one stationary and one moving pad. I'd have to compare setup instructions side by side but can't think of a difference off the top of my head (well, other than the old version used magnets instead of a spring to retain pads). I've been using them since they came out, have both old and new models.




BTW, if you search for my thread about the rotor torque and vibration issue, you'll find that Avid stands by their recommendation etched into the rotor (6.2 N*m) even though the manual says 9-10 N*m. They claim the manual torque is a misprint but I had the vibration using 6.2 and didn't after upping it to 9.5. YMMV.

I doubt increasing torque on such small screws is a good idea in any case, the lower torque is sufficient and breaking off the head of a screw in your hub might not be any fun. I hadn't noticed the misprint on the current manual on their site, though (and it's there right now, just had a peek). Harmonic vibrations happen with rim brakes on some bikes, too FWIW; I'd guess it had more to do with readjusting your caliper (but I haven't looked at your other thread either for more details).

Not sure what you're thinking about but the BB7 (formerly BBDB) is virtually the same since inception, still one stationary and one moving pad. I'd have to compare setup instructions side by side but can't think of a difference off the top of my head (well, other than the old version used magnets instead of a spring to retain pads). I've been using them since they came out, have both old and new models.

My guess is that frankenmike is referring to both or one of the pads being adjustable. On the BB7 both pads can be adjusted in and out though only one pad moves whereas on the BB5 only one pad can be adjusted and again only pad moves.


I doubt increasing torque on such small screws is a good idea in any case, the lower torque is sufficient and breaking off the head of a screw in your hub might not be any fun. I hadn't noticed the misprint on the current manual on their site, though (and it's there right now, just had a peek). Harmonic vibrations happen with rim brakes on some bikes, too FWIW; I'd guess it had more to do with readjusting your caliper (but I haven't looked at your other thread either for more details).

Can you point me to the online manual that shows 6.2 N*m for the rotor bolts? This online manual shows 9-10 N*m: http://www.sram.com/_media/techdocs/08%20BB7%20User%20Manual%20Rev%20C.pdf

Here's a link to my other thread: http://www.bikeforums.net/showthread.php?t=499350

Do note that this was NOT a harmonic vibration. I've experienced squealing brakes before and this vibration was nothing like that. The whole bike shook so much that the cables rattled against the headtube.

My guess is that frankenmike is referring to both or one of the pads being adjustable. On the BB7 both pads can be adjusted in and out though only one pad moves whereas on the BB5 only one pad can be adjusted and again only pad moves.



Can you point me to the online manual that shows 6.2 N*m for the rotor bolts? This online manual shows 9-10 N*m: http://www.sram.com/_media/techdocs/08%20BB7%20User%20Manual%20Rev%20C.pdf

Here's a link to my other thread: http://www.bikeforums.net/showthread.php?t=499350

Do note that this was NOT a harmonic vibration. I've experienced squealing brakes before and this vibration was nothing like that. The whole bike shook so much that the cables rattled against the headtube.

It could be frankenmike is confusing the BB5 and BB7, although they really have very little in common, the BB5 isn't on the same level in several respects. I did think that both pads were adjustable on the BB5, just that one does not have a dial adjuster but rather needs an allen or torx wrench to adjust or uses cable tension instead, but no personal experience there.

I'm sure my printed literature with my BBDB/BB7 brakes specified the lower torque value (6.2 Nm) as printed on the rotor for the rotor bolts. Perhaps when having someone update their online version something went wrong, but it doesn't make sense to me that both the larger caliper and smaller rotor bolts/screws would have the same torque value simply due to the size differential. Squealing is not what I mean by harmonic vibration, disc brakes simply sometimes squeal due to temperature or moisture. I've never had the problems with the chattering/grabbing some report, feel that's usually due to poor setup/adjustment or contamination. I've even successfully reinstalled BBDB/BB7s for friends that have had problems, some just don't take the care needed. YMMV.

I'm sure my printed literature with my BBDB/BB7 brakes specified the lower torque value (6.2 Nm) as printed on the rotor for the rotor bolts. Perhaps when having someone update their online version something went wrong, but it doesn't make sense to me that both the larger caliper and smaller rotor bolts/screws would have the same torque value simply due to the size differential.

I have two sets of printed literature for BB7 brakes (one road, one MTB) and both say 9-10 N*m. What revision of the literature do you have that is says 6.2? (all out of curiosity of course)


Squealing is not what I mean by harmonic vibration, disc brakes simply sometimes squeal due to temperature or moisture. I've never had the problems with the chattering/grabbing some report, feel that's usually due to poor setup/adjustment or contamination. I've even successfully reinstalled BBDB/BB7s for friends that have had problems, some just don't take the care needed. YMMV.

With my set up, I did everything the same the first go around as I did the second, only the second time around I applied more torque to the rotor bolts and the vibration went away. I am willing to admit that there might have been a small difference between both set ups (it would be less likely for there to be no difference as it would be impossible to EXACTLY duplicate the original set up). But, there is no way that the tiny difference that inadvertently occurred during resintallation made the difference between a brake that felt like it was trying to buck me off the bike and one that slows me down without a hint of chatter. If I get bored someday, I'll confirm this by uninstalling and reinstalling the rotor but using the original torque without touching the caliper. There is very little incentive to want to relive that experience though.

What kind of sloppy set ups have you come across that have caused vibration?

...First, after you adjust the pads out, give the brake lever a couple of good squeezes to set the pads in place. I found that while the pads would sometimes rub right after an adjustment, actuating the brakes a few times would alleviate some of the rotor rub. ...

This was my problem. Thanks!

This was my problem. Thanks!

Yep, making sure the pads are firmly seated is a good thing...

This was my problem. Thanks!

Cool, it took me few aggravating adjustments of the pads before I realized this too. I was only gently squeezing the lever at first which didn't quite cut it.

Hey, Fool!

Yeah, it did sound like BB5s rather than BB7s, although the newest BB5s do have dials for both. Also no mention of checking the straightness of the rotor.


It could be frankenmike is confusing the BB5 and BB7, although they really have very little in common, the BB5 isn't on the same level in several respects. I did think that both pads were adjustable on the BB5, just that one does not have a dial adjuster but rather needs an allen or torx wrench to adjust or uses cable tension instead, but no personal experience there.

I'm sure my printed literature with my BBDB/BB7 brakes specified the lower torque value (6.2 Nm) as printed on the rotor for the rotor bolts. Perhaps when having someone update their online version something went wrong, but it doesn't make sense to me that both the larger caliper and smaller rotor bolts/screws would have the same torque value simply due to the size differential. Squealing is not what I mean by harmonic vibration, disc brakes simply sometimes squeal due to temperature or moisture. I've never had the problems with the chattering/grabbing some report, feel that's usually due to poor setup/adjustment or contamination. I've even successfully reinstalled BBDB/BB7s for friends that have had problems, some just don't take the care needed. YMMV.