carcassonne

Folks,

I'm relatively new to disc brakes in general. And in montain biking which means that I apply brakes more often than experienced riders do, although I'm becoming more confident in my skills now. So, for the regular cleaning/maintenance of the bike I tried to get the rear brake mechanism as tight as possible (eg. as close as possible wihtout rubbing) when I noticed that when doing that the disc rotor would rub only during a small part of the circumference as I tighten up the barrel at the brake lever. The brakes are Avid BB5.

Taking a closer look in the gap between the rotor and the pads I saw that indeed the rotor was out of true as it seems. Torx screws are holding the rotor to the hub and the screws seems well in place. So I located the place of the rotor where it went against one of the pads and applied a bit of pression in the other way using my fingers. To my surprise this produced an effect.

So this is new to me, that disc rotors can warp and, can respond to finger pressure. I thought these things would be made of some kind of very strong metal and would always stay straight in normal use.

My question then: is disc rotor truing a common thing to do ? If so, is there a way to easily mesure the trueness (eg. like truing wheels in a truing stand) and are there tools to do this ? And lastly, if there are tools to do that, is it worth while to invest in them of woudl fingers or a pair of long nose pliers or some such be OK ? - Thanks.

Cheers,
Al

Dan Burkhart 

Disc rotors are only 2 mm thick, so no matter what they are made of, warpage can happen. Your friendly neighborhood LBS will likely have a set of Morningstar drumsticks hanging on the wall to deal with this.
And yes, it is a common thing.

Wordbiker

If you have a Park truing stand, there is a rotor truing attachment available for it. Even better is the dial indicator "upgrade". Using the DT-2 rotor truing fork with these has allowed me to straighten rotors I'd previously just throw away.

Rotors that don't rub make customers much happier with disc brakes.

norco_rider77

morningstar drumsticks, what are those? and what do they ? or are they seriously drum sticks, for playing drums?

Dan Burkhart 

It is a set of 3 tools which vaguley resemble chicken drumsticks. They have slots cut into them to slip over the rotor. The operator holds the outer 2 tools steady while using the one in the middle to gently pull the warped section of rotor straight. Park makes a version of this tool set as well, and I'm sure it works just as well, I just happen to use the Morningstar set.

apoq

coming in late, i know, but i have the same brakes, Avid BB5 and the same problem. From the get go i noticed the rubbing of the pad on the rotor from the sound it made. The guys told me it was just a matter of braking in the new brakes but, being obsesive compulsive i fidled around there and found that the rotor seemed to be warped. Is this an issue that i should solve by warranty rights or should i just try to straighten it out?

Asymmetriad

Adjustable wrench got my BB5 rotor straight in ten seconds.

Freefallman

Do the pads need to be as close as possible to the rotor? I mean as long as the caliper clamps the rotor completely before it runs out of cable it would seem to fine to me. Am I off base on this?

Black Bud

You need not set the pads in very close, and it may not even be advisable for you to do that while you get used to discs. However, you don't want to set them so wide as to almost run out of cable before the brake engages since cables do "stretch";you don't want to be caught with too much cable and too little "pull" out on the trail (or anywhere else!) Yes, there are adjusters so this problem can be 'fixed' on the "fly", but the time that a "problem" is paid attention to is all too often the time the "fix" should have been made several miles beforehand...