Squealing BB7s
 

I run BB7 road discs on my commuter. When I switched to Shimano centerlock hubs with Shimano rotors (LX level...I forget the exact model number) the rear started screaming.

I've painstakingly set them up, and re-checked the setup. It's perfect.

I've cleaned them.

The front works great, and doesn't shriek.

The rear is pretty consistent in it's protests.

Do I need different pads?

Shimano rotors tend to have narrower braking tracks than the pad of the BB7, you sure it's a good match in your case?

Hadn't considered that as a potential source of squeal, so I didn't exactly break out the calipers to measure. I double checked that what both rotors claimed as 160mm was actually 160mm (it was a match) but other than that I just eyeballed it.

The scuffing from the pads looks well aligned, even if the Shimano rotor has a slightly narrower track.

I really like the center lock mounting system. Unfortunately Avid doesn't make any of their own rotors center lock compatible. And the adapters are kind of kludgy.

I'm glad Avid doesn't do centerlock as have no interest in locking myself into those hubs/rotors :D

Braking track and diameter aren't the same thing...don't want overlap on your pads vs rotors...or vice versa

If the front isn't squealing, it doesn't seem likely that you'd have an overlap issue in the rear. However, I know that when I've had a standard brake pad hanging a bit off the edge of the rim it squeals terribly so it's probably worth looking into. Pull the pads and if they are contacting the rotor completely.

sounds like you need a new rear rotor set up

Possible, depending on the type of dropout in the rear. Placement of the caliper in relation to the rotor may be off. We're assuming it's not a horizontal dropout since most disc bikes aren't, but until the OP gives us more it's just an assumption.

Banzai, how did you clean the rotors? That may be an issue too. Alcohol works best.. The rotors should say on them what pad material they're designed for. It's usually laser etched near the hub.

After using the BB7's personally on two bikes: have the disc tabs faced.

Even though Avid has their domed washer adjustment to compensate for slight alignment issues, if the brake is squealing, something is resonating. Even a little paint can allow movement of the caliper. Having a solid mounting surface after facing took all the squeal out of my BB7's.

Good point. I hadn't even considered that.

In that case, Banzai, have you checked and double checked that your rear wheel is sitting in the dropouts correctly?

Vertical dropouts. Horizontal is just stupid with discs...

I'll try the alcohol, and I'll also search for that etching.

Because of the domed washers you mention, I never considered this. Afterall, the tabs look right to me, and whatever error there may be was, in theory, taken care of by those washers.

It's curious to me that with Avid's roundagon rotors there would be no squeal though. I wonder if the much greater number of holes drilled in the Shimano rotors are causing this.

Oh yeah, but someone out there is doing it I'm sure :)

I've seen pictures. The dropout slides indepently of the frame and the disc mount is part of the dropout. No alignment issues with that set up.

The Avid CPS and pad dial adjustments can make you think they're enough to line your pads up square to the face of the rotor and that's not always true, I check mine very carefully and sometimes have to make some sort of finer adjustment (especially when you're right on the edge of the caliper's ability to move side to side, I've used washers/spacers to move the caliper to give a bit more freedom of movement when you tighten down the cps stack). I found this more true of my recently acquired Elixirs to get them centered exactly, but have done so with BB7s on a few bikes (and different hubs' tolerance can affect that also).

Well, Surly for one does not agree. I've built up a couple of 1x1 frames which have rear facing horizontal dropouts with disc brakes.
http://www.surlybikes.com/1X1.html
Had no issues with either one.