[Tenchiro]

I purchased a 2002 Giant AC2, with Hayes Hydro's and 8" rotors. I broke them in according to the instructions on Hayes website. The front brake is great, but I can't seem to get the rear to not rub. When the wheel spins I can see a slight wobble in the rotor, but not so much that is hits the caliper. I dunno if this qualifies as a warranty replacable item. The mechanics where I bought the bike, have not been able to do anything but make it worse...

I set it up so that it is perfect and does not rub or make any noise, and did a short test ride. I came back a few hours later and it rubbed the caliper in all parts of it revolution. I basically took the caliper off the bike, pushed the pistons all the way in, and used the business card trick to set it up.

If I set it so it doesn't rub when I am off the bike, it does when I am on it. But I can't seem to set it so that it doesn't rub when I ride. Plus, once the rotor warms up, it screws ell my previous adjustments up as it seems to totally ride differently.

Any good mechanics in the Seattle area that can help?

Thanks

EDIT -- Is there a good way to shim those sloppy ass levers. They are so noisy, and always feel the the bolt is really loose.

 

[Shibby]

Try tightening the rear hub. Loose hubs with disc brakes have caused many a headache.

 

[Rustmouse]

Something that people tend to do with disks is eyeball them when they're torquing em down onto the hub... It's best if you use a torque wrench, but you can make do without... Just make sure you tighten the bolts holding the disc in a couple of stages, and ensure the torque is the same on all of em (uneven torque will warp even automotive disks!) It also helps to keep em tight if you clean the bolts and use blue Loctite (threadlocker) on em.. that way you don't have em backing off due to heat and vibration.

 

[rfemurfx]

tanchiro, to asnswer your question; what you need to look at is where the caliper's center sits in relation to the disc. once you've done the "card trick" look at the caliper and the gap on both sides of the rotor, it should be even.
if it is not even take note how much more adjustment you have on the caliper. do that by removing one mounting bolt and looking at the oval and noticing where the bolt hole is. if the caliper cannot be move anymore in the direction that needs to go in order to center it over the rotor, then you may need to use some shims in between the brake adapter and the frame to move it over enough.
if that is not the case and the caliper IS centered over the disc and when you use the brake the pads go back to rubbing then one of the pistons is not fully retracting. you can fix this by removing the caliper and pad of the piston which is not moving properly, once removed hold the other pad in place while squeezing the lever about 3-4 times. WATCH THE PISTON, SO YOU DONT PUSH IT OUT! do that several times until both move equaly.

if you set a caliper up off-center the piston to which the rotor is closest tends to freeze up. that is due to lack of movement and therefore lack of lubrication of the quad ring.

 

[rstrange1]

Giant sometimes welds their disc brake hangars on incorrectly. check if it is angled. You may need a new frame if your rotor isn't bent. Some people true rotors with 2 adjustable wrenches. (Not reccomended.)

 

[rfemurfx]

if you dics tabs are welded crooked or not parallel from each other you can get this fixed. there is a tool made by magura that faces the disc tabs so any miss-alignment can be corrected. it is called "GNAN-O-MAT" and any shop can buy it but not many have it. that tab mis-alignment is not only on giants, its practicaly on every frame.

 

[Tenchiro]

Thanks for all the reponses. I think I finally have it adjusted. But I still get some rubbing under heavy torque, which I think I can live with.

 

[Dave]

8" rotors are very hard to get not to rub.

 

[joE_2k2]

The larger Hope rotors have this problem too. Because bigger rotors offer more leverage, it is more prone to buckling/warping.This is why I'm changing my troublesome front disc (185mm, I'm on my 3rd now, and its perfectly aligned) and caliper to a smaller disc and caliper (165mm) on my '99 Junior Ts.