Dirt bike’s hand-operated front brake is vital to safely navigate rough terrain. A damaged brake will place the rider in a dangerous situation. Most brake problems are caused by a loss of hydraulic pressure or front wheel instability. Hydraulic pressure loss is caused by leaks within the brake lines or fittings, allowing air and contaminants into the system and creating a spongy feeling at the front brake lever. Instability is caused by a warped brake rotor and appears as a violent shudder when braking. Repairing these problems can be performed with basic tools, but requires some familiarity with your motorcycle.
Restoring Hydraulic Pressure
1) Restore hydraulic pressure within the brake system by replacing any leaking, worn or damaged fittings and hoses.
2) Remove the cap from the master cylinder’s fluid reservoir and suck out as much of the fluid with a hand pump as possible. Refill the reservoir with fresh brake fluid.
3) Locate the bleed valve on the front brake caliper and remove its rubber dust cap. Slip a length of clear plastic hose over the valve, placing the opposite end into a jar or container.
4) Turn the valve counter-clockwise a quarter turn with a 6 mm wrench to open the valve. Pull in and hold the front brake lever to force a small amount of brake fluid out of the valve. Close the valve, turning it a quarter turn clockwise with a 6 mm wrench. Release the brake lever. Repeat until the fluid trapped within the hose has become clear and free of bubbles or debris.
5) Remove the plastic hose and wipe away any spilled brake fluid with a clean shop towel. Top off the reservoir with fresh brake fluid and replace the cap. Pull in the front brake lever to check the hydraulic pressure. A firm pull should be required to engage the front brake. If the lever still feels soft or spongy, repeat Steps 1 though 4 and inspect the brake system for leaks.
6) Place the motorcycle on a stand or lift to raise the front wheel off of the ground.
7) Remove the front brake caliper, using an Allen key to unbolt it from the front fork. Slide the caliper off of the front brake rotor and suspend it from the handlebars with a bungee cord.
8) Remove the front wheel, using a socket wrench to remove the front axle lock nut. Tap the front axle out of the front fork with a rubber mallet and lower the wheel to the ground.
9) Unbolt the front brake rotor from the wheel using an Allen key. Install a new brake rotor onto the wheel. Reinstall the front wheel onto the motorcycle, sliding the front axle through the front fork and wheel. Screw the front axle lock nut into place and tighten with a socket wrench.
10) Slide the front brake caliper over the rotor. Use an Allen key to tighten the caliper’s bolts. Lower the motorcycle from the stand.
* Do not attempt these repairs if you doubt your ability to complete the job properly. Instead, have the work performed by a qualified motorcycle technician.
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