If you're the easily frustrated type little else probably raises your ire than a bit of brake drag.
It's annoying, ruins your ride and finding the root cause takes some investigative work. If you've never had the privilege, brake drag feels like something is holding you back. It's pinned but speed isn't there and you swear your dirt bike keeps braking but you're not applying the brakes.
Brake drag or grabbing most often occurs on the back wheel which explains a little of its shrouded nature. When it happens in the front it's much more discernible and if it's bad enough you probably can't ride your bike. In either case, once brake drag is indicated start from the often (and hopefully) easy fix then work your way to the much harder solution.
The Problem is You
Riders generally rest their foot on the brake pedal while riding which normally isn't a big deal unless you're resting a bit too comfortably and inadvertently applying the brakes. Usually though, the pedal is adjusted incorrectly so even slight pressure engages the brake system. Adjust the pedal at the master cylinder above the clevis.
Rocks and Debris
It's not uncommon for a rock to get stuck or mud and grime to build up in between the pads and rotor causing friction. Rocks and dirt also interfere with the caliper putting unnecessary force on the pad to the rotor. A thorough cleaning of the brake system eliminates the problem just double check the caliper and pads remain aligned before heading out.
Bent or Warped Rotor
Place your dirt bike on a stand and spin the affected wheel. Does it flow smoothly or is there an obvious hang-up? If it's bad, you'll hear it rub. You just might have a bent or warped rotor. Wheel alignment could also be an issue.
Check for kinks, damage or other restrictions to the brake lines. Sometimes crashes or just riding in general results in twists and turns ultimately pinching the brake lines.
First check the brake fluid in the master cylinder. Is it dirty? If so, change it. Next, check that the plunger/piston works effectively and doesn't leak. The plunger should move back and forth freely when applying the brakes. Check out the diagram of a function brake system:
Additionally, when releasing the brakes the plunger returns to a "resting" state as brake fluid returns to a reservoir until the next time you apply the brakes - this pushes the plunger in, along with the fluid to squeeze the pads together via the caliper. If a blockage occurs, the reservoir remains dry which builds pressure ultimately leading to the brakes locking up. This can also damage the pads, rotor and caliper. Any master cylinder problem requires a rebuild and this kit should do the trick.
A thorough inspection of the brake system covers the pads and pins to ensure correct installation and good working order. Replace any pins or the caliper (front caliper) if damaged. Also, double check the caliper pistons readily move without sticking and make sure the brake pad spring is installed correctly.
Finally, regular cleaning and maintenance is your best line of defense. After riding, clean the brake system, remove dirt and debris, and inspect the pads, caliper, pins and bracket for damage and proper function. Apply brake grease (yes, grease specific to brakes) to the pad clip areas of the caliper and bracket, on the back of the pads lightly where they contact the caliper piston, on the hanger bracket pins, and lightly on the pad pin surface.
Want to know more about dirt bike brakes? Check out: