Bleeding the Brakes on a 2017 Honda CBR300R ABS

Shop parts for a 2017 Honda CBR300R ABS Motorcycle.

Why and When to Bleed the CBR300R ABS Brakes

Brake fluid is a consumable, even though it lives in a sealed system. Over time it pulls moisture out of the air through the reservoir vent, and that moisture does two harmful things: it lowers the fluid’s boiling point, so hard, repeated braking can boil the fluid and give you a soft, fading lever, and it corrodes the master cylinder and calipers from the inside. That is why many riders flush the fluid on a schedule whether or not anything feels wrong.

Bleeding is also the fix when air has entered the system. Air compresses where fluid does not, so a lever that feels spongy, pulls closer to the grip than it used to, or slowly sinks while you hold it is telling you there is gas in the lines. Air gets in whenever the hydraulic system is opened — new brake lines, a caliper rebuild, master cylinder service, or simply letting the reservoir run dry while you were working on something else. If you have just done any of that work, plan on a bleed before the bike goes back on the road.

What the 2017 CBR300R ABS System Looks Like

Your 2017 CBR300R ABS uses hydraulic disc brakes at both ends, with a hand lever operating the front caliper and a foot pedal operating the rear. Because the model carries the ABS designation, an anti-lock modulator sits in the hydraulic circuit between the master cylinders and the calipers. That matters for one reason: a normal bleed at the caliper bleeders is the right way to refresh fluid and clear air from the lines and calipers, but the ABS unit itself is a different story. If the reservoir ran dry, or if the ABS unit or its lines were disconnected, air can be trapped inside the modulator where a hand bleed will not reach it. That situation calls for a dealer-level procedure or diagnostic tool, so plan on a shop visit rather than trying to force it at home.

The CBR300R ABS is not a linked-brake machine, so the front lever and rear pedal work independently and you bleed each circuit on its own.

Tools and Supplies to Have Ready

  • Fresh brake fluid of the type printed on your master cylinder reservoir cap, from a sealed container — fluid that has been open on a shelf has already absorbed moisture
  • A box-end wrench that fits the bleeder valve snugly
  • A length of clear tubing that fits tightly over the bleeder nipple
  • A small catch bottle for the old fluid
  • Rags or shop towels, plus water for rinsing
  • A syringe or turkey baster for pulling old fluid out of the reservoir
  • The correct driver for the reservoir cap screws
  • Optional: a one-way check-valve bleeder or a vacuum bleeder, both of which make a one-person job much easier

Setting Up Before You Open Anything

Get the bike on a stand so it is upright and stable, and turn the handlebars until the front reservoir sits level. Brake fluid attacks paint and many plastics on contact, so drape rags over the tank, the fairing panels, the instrument cluster, and anything else below the reservoir before you touch a screw. If a drop does land on a painted surface, wipe it immediately and rinse the area with water rather than rubbing it in.

Bleeding the Front Brake, Step by Step

  1. Remove the reservoir cap and diaphragm, then use the syringe or baster to draw most of the old fluid out. Leave a little at the bottom so you do not push air into the master cylinder.
  2. Refill with fresh fluid to the upper level mark.
  3. Push the clear tubing onto the front bleeder valve and route the other end into the catch bottle, with a little fluid already in the bottle so you can see bubbles.
  4. Fit the box-end wrench on the bleeder, then squeeze the front lever and hold it.
  5. With the lever held, open the bleeder about a quarter turn. Fluid and air will push out through the tube.
  6. Close the bleeder before you release the lever. Releasing with the bleeder open draws air back in.
  7. Repeat squeeze, hold, open, close, release until the fluid coming through the tube is clean and free of bubbles.
  8. Check the reservoir after every few cycles and top it off. Never let it run low enough to pull air.

If your bike has two front calipers, bleed them one at a time, and start with the caliper farthest from the master cylinder.

Bleeding the Rear Brake

The rear circuit follows the same logic with the pedal in place of the lever. Remove the old fluid from the rear reservoir, top it with fresh, attach the tube and bottle to the rear bleeder, then press and hold the pedal, open the bleeder a quarter turn, close it, and release. Keep working until the fluid runs clean and bubble-free, checking the reservoir level as you go.

Finishing Up and Checking for Leaks

When both circuits run clean, tighten each bleeder snugly — firm enough to seal, without cranking on it hard enough to damage the seat. Fill the reservoirs to the correct level marking, reinstall the diaphragms and caps, and wipe down every surface that saw fluid. Then look closely at the bleeder valves and the banjo fittings at the master cylinder and caliper for any weeping, and check again after the bike has sat for a while.

Testing Before You Ride

The lever and pedal should feel firm and consistent, and should hold pressure without slowly sinking while you keep a steady squeeze on them. Spin each wheel by hand to confirm the brakes are not dragging. Then, in a safe, low-speed area, test the brakes gently before riding normally.

When to Stop and Take It to a Shop

If the lever will not firm up after several rounds of bleeding, if it only firms up when you pump it, if bubbles keep appearing no matter how long you work, or if you see fluid weeping from the master cylinder or a caliper, stop and have the bike inspected. Any suspicion that air reached the ABS unit is also a shop job. Brakes are not the place to keep improvising.

Related Shopping Categories

Shop Brake Fluid for a 2017 Honda CBR300R ABS Motorcycle.

Shop Brake Lines for a 2017 Honda CBR300R ABS Motorcycle.

Shop Brake Pads for a 2017 Honda CBR300R ABS Motorcycle.

Shop Stands for a 2017 Honda CBR300R ABS Motorcycle.

Shop Brake Tools for a 2017 Honda CBR300R ABS Motorcycle.

Disclaimer: This guide is provided for general informational purposes only and is not intended to replace your motorcycle's official owner's manual. Always refer to your manufacturer's documentation for model-specific instructions, torque specifications, safety procedures, and maintenance requirements. If you are unsure or inexperienced, consider seeking assistance from a qualified mechanic or technician.