Brake Drag and wheel binding?
Excessive brake drag is usually caused by one of several possible culprits:
1) Warped backplates; if your pads aren't flat, you'll definitely experience greater brake drag as when the lever is released and the caliper pistons are retracted from the pads, the you'll still have rotor/friction material contact since the seals can only retract the pistons a very small fraction.
2) Misalignment; if the wheel/caliper/fork assembly alignment is off, binding of the assembly will often occur (bent axles and triple-clamps will be a problem here too). This is particularly true if assembled and tightened while on a front wheel stand (attaching from the fork bottoms). Best way is to have everything assembled but not tightened on the stand, then let it down and bounce the fork/wheel a few times to center everything, then tighten.3) Poor Piston Retraction: Poor piston retraction can be a major culprit and cause of rotor over-heating and distortion, accelerated pad wear, and glazed friction surfaces (creating brake squeal, etc.). Check to make sure all pistons are not only moving freely in their bore, but are retracting as well (when the lever is released). You'll need to block the other pistons to isolate the individual your checking, alternate one at a time. If then suspect, replace all piston seals (we recommend this regardless with a used or suspect caliper).
4) Excessive deposition layer build-up: all friction materials impart a thin transfer layer on the brake rotors pad track. This is a normal part of the bed-in process. But some transfer more than others, creating an excessive and/or uneven build-up that can cause problems with brake drag, brake judder and deteriorating performance. Suspect rotors should be bead-blasted or rotor honed if you don't have access to the blast cabinet (Racers: do this at least every third race weekend, more often if possible). For best results, it is recommended to perform this regiment every time you change friction materials!
5) Disc Thickness Variation: A DTV of over +.0005" can often result in brake vibration. Although not common, is does occur. Suspect rotor should be carefully measured with an accurate 0-1" micrometer by an experienced technician.