The phrase, “gas is your friend” is a popular one in some ATV riding circles. It means that, contrary to popular belief, squeezing the throttle a little more might actually help you out of a jam, like when the rear end starts to swap from side to side over a set of moguls. Brakes are your friend, too. Here are a few tips on how to perform ATV brake service on an ATV disc brake system.
The first step in ATV brake service is to remove the wheel to expose the caliper and brake rotor for service. But before you dismount the caliper, loosen the brake pad mount hardware. If you first remove the caliper and then try to loosen the bolts, you might not be able to hold the caliper firmly enough to get good leverage. With the brake pad bolts loose, remove the caliper from the mount; it’s often fastened with two Allen bolts.
Remove the pad hardware and pull the old pads out of the caliper. If the pads pushed together while you were messing with the assembly, wedge a flat screwdriver between the pads to separate them. Inspect the brake rotor for gouges and other damage. If you have the manufacturer’s specification and the means to take an accurate measurement — a micrometer — make sure the rotor hasn’t worn too thin. Replace the rotor if it’s damaged or worn.
Install the new pads in the caliper, but make sure you don’t contaminate them with grease. If they are soiled, spray them with brake cleaner and wipe clean. With the pads in the caliper, remount the caliper to the ATV and reinstall the wheel.
Another important step of ATV brake service is to flush the brake fluid. Brake fluid is hydroscopic, meaning that it absorbs water, and water degrades brake fluid because it promotes corrosion within the brake system and it reduces the brake fluid’s boiling point. A reduced brake fluid boiling point can lead to brake failure and all-out brake system failure.
To flush the brake fluid, remove the wheel if necessary to gain better access to the brake caliper. Attach a clear rubber hose to the brake fitting on the caliper and feed it into a container like a water bottle. This will help contain the old fluid as it’s purged from the caliper and protect hard parts from corrosion caused by the brake fluid.
Loosen the fitting with a wrench about a quarter turn and have a helper slowly squeeze the brake lever/pedal until it bottoms out against the handlebar or floorboard. Fluid should flow out of the caliper, but if it doesn’t, loosen the fitting a little further.
Close the fitting and then have your helper release the brake lever. Now loosen the fitting again and have your helper gently squeeze the lever/pedal again to purge more old fluid from the system. Tighten the fitting and release the lever/pedal. Continue this process until all of the brake fluid has been evacuated.
With the system empty of fluid, remove the master cylinder cover and add new brake fluid to the reservoir. Your ATV will likely require DOT 3 or DOT 4 brake fluid, refer to the master cylinder cover and add the type of fluid that’s spec’d on the cover.
With the reservoir filled to within roughly one-quarter of an inch from the top, have your helper gently squeeze the lever to push new fluid into the brake line and bleed out the air. After about five pumps, hold the lever to the bar and then loosen the fitting in the caliper; air will purge out.
After a few cycles, the system will start to build pressure and fluid will start to come out of the fitting. Continue to add new brake fluid to the reservoir and bleed the air until your helper feels firm pressure and air no longer bubbles out with the fluid.
Clean up spilled brake fluid with brake cleaner and a shop towel. Brake fluid is corrosive, so be sure to clean all affected parts. Test the brake system before you hit the trail.
