Really not too off topic: disk brake question

[PATRICK MOORE]

I say "not too off topic" since the brakes in question are on the
Fargo which is quite Rivendellianishly (gad, how's that for a cobbled
together adverb? Rivishly?) set up and, moreover, the disks are really
the only brakes that will allow quick wheel changes between 27 mm rims
and 44 mm rims.

Anyway: The front Avid BB7 rotor has been bent and rebent and is now
rather wavy and just barely nicks the pads as it goes by -- so
slightly that feathering the brake will stop it for a half mile or so;
but it comes back. I don't want to back off the pads any further. Does
anyone have any instructions or can anyone point me to instructions on
the web for getting a slightly wavy disk (160 mm) back into plane?

The exactly similar disk on the Kojak wheelset is centered fine, as
are both rears.

The "shish-shish-shish" sound was rather annoying just now on my afternoon ride.

Thanks.

--
"When in Rome, do as they done in Milledgeville."

Flannery O'Connor

-------------------------
Patrick Moore, Albuquerque, NM, USA
For professional resumes, contact Patrick Moore, ACRW
http://resumespecialties.com/index.html
-------------------------

[Peter Morgano]

I had a smiliar problem on a Giant Traverse (I know, I know) that used to be my around town ride. LBS said that if you were good with soft hammer on a work bench/bench vise you could do it but really to just buy new discs if you want it to be "perfect."

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[Jim Mather]

Park actually makes a rotor truing tool:
http://www.parktool.com/product/rotor-truing-fork-dt-2

And a Youtube how to: http://www.youtube.com/watch?v=nHdQkm14JVw

jim m
wc ca

[ascpgh]

I built a Karate Monkey as a drop bar, disk-braked (BB-7), all-weather commuter and will occasionally suffer some pad drag that plays the high spots of any nominal wobble of the rotating rotors. Will resolve after some lesser force applications of the brakes, probably starting to get a bit reluctant to respond to the recoil spring that retracts the moving pad. Mine is growing some collective recalcitrance beyond cable drag in this function, I've probably exceeded the design life with the amount of environmental exposure to which I've subjected these great little brakes. This bike started as an experiment that could be terminated on a frame that could have cantilevers installed the day I soured on the disks. 

 I chose the biggest disk diameter (185mm at the time) so that there was more swept area and more material across which to share any necessary truing or tuning. In my mind truing smaller diameter rotors seemed more likely to get out of hand quicker as any any adjustment to effect change of a dimension at the braking surface would require a greater angle to be formed compared to larger diameters. Seemed like a way to avoid replacing rotors more often. 

Mine are at the six year mark and I am likely to replace the calipers themselves (or pen a whole new commuter project) before the rotors due to accumulated degradation of all exposed surfaces and mechanisms. I completely get the non-Riv argument about disks but after my ride last Sunday at the annual Pedal Pittsburgh long loop where the final 15 miles were logged climbing up onto Mt. Washington then across the ridge line it creates via drops down into neighborhoods then back up to the crest with a finale of a four mile descent through the forests of Glass Run, all in a pouring down heavy rain. My Rambouillet ate a complete set of brake blocks over the course and those rim brakes, bathed in the volume of water we rode in, were nearly to zero effectiveness. Thank goodness for familiarity of the roads and frequent communication with others to keep things from becoming too much of a scare. The discs in the group functioned remarkably and those riders were amazed by how flustered others were over wet rim braking.

Andy Cheatham

Pittsburgh, PA

[PATRICK MOORE]

Thanks for the replies. After reading, I looked online at replacement
rotors and see that you can get them for under $10, so that is a way
out. The video was very helpful in that it reduces to clear, discrete
steps the rather blundering and intuitive approach I was trying. I'll
use a crescent wrench for now.

I don't think my calipers are bad, since, again, it is only this one
disk that offends: the other three are fine. But I do have, I think, a
spare set in the box when that time arrives.

[Mark Chandler]

Truing rotors can be pretty difficult.  Before attempting to true a rotor, always make sure that the mounting bolts are properly tightened.

I've also found that this stuff works well for getting rid of "flutter":

http://www.gravelbike.com/?p=1177 

[PATRICK MOORE]

Thanks; must look at those bolts. And I'll remember Squeal Out if a
rotor starts squealing.

Maybe I'll remove the rotor, place it on a metal slab, and beat the
hell out of it. It will make me feel good, even if it does no good to
the rotor. I'm glad I no longer have 185s or whatever -- more chance
of bending.

That -- bending -- is the sole liability of disks, at least mechanical
ones (I've not used hydraulics). I used to shove wheels in the back of
the car, or else sling them up against a wall and this front rotor has
paid the price before I realized I had to be careful. Also they don't
modulate as well as my goodest calipers (single pivots -- old SunTour
S Pro? -- with worn in Kool stops are as good as any dual pivot I've
used, and modulate better) or nice wide profile cantis but otherwise
they are very nice for fast wheel swaps and not worrying about
grinding down expensive rims during sand riding and no g-dum housing
hangars, balky QR mechs, and such.