Bleeding the Brakes on a 2017 Honda CBR300R

Shop parts for a 2017 Honda CBR300R Motorcycle.

How the CBR300R's Brake System Is Configured

The 2017 CBR300R stops on hydraulic disc brakes at both ends. Up front, a single caliper is fed by a master cylinder mounted on the handlebar; out back, a second caliper is driven by a pedal-actuated master cylinder near the right footpeg. The two circuits are completely separate, which means each one gets bled on its own and neither one can be fixed by working on the other.

Honda sold this model in both standard and ABS form, so take a moment to identify what is sitting in your garage. An ABS-equipped bike will have a tone ring and wheel sensor at the hubs and an ABS indicator on the dash. That distinction matters later: routine fluid replacement through the caliper bleeder is the same job either way, but if air has migrated into the ABS modulator, the home procedure below will not clear it. This bike does not use a linked or combined braking system, so the front lever works the front brake only and the pedal works the rear only.

Signs That the Fluid Needs Attention

Brake fluid is hygroscopic, meaning it pulls moisture out of the air over time. That absorbed water lowers the fluid's boiling point, and a brake that fades on a long downhill or during repeated hard stops is often suffering from old fluid rather than worn pads. Many riders simply refresh the fluid on a schedule instead of waiting for a symptom, and on a lightweight sport bike like the CBR300R that habit pays off.

Bleeding is also the right response to a lever that feels spongy or pulls closer to the grip than it used to, a pedal with a soft, vague feel, fluid that looks dark or cloudy in the reservoir sight glass, or any recent work that opened the hydraulic system — new lines, a caliper rebuild, or master cylinder service. Air is compressible and fluid is not, so any bubble trapped in the circuit turns lever travel into mush instead of clamping force.

Tools and Supplies to Collect First

  • Fresh brake fluid of the type printed on your master cylinder reservoir cap, from a sealed container. Do not substitute a different specification.
  • A box-end wrench that fits the bleeder valve snugly — a snug fit matters more than the size on the stamp.
  • Clear tubing that pushes firmly over the bleeder nipple, plus a catch bottle to hang it in.
  • A syringe or turkey baster for pulling old fluid out of the reservoir.
  • The correct driver for the reservoir cap screws.
  • Rags or shop towels, plus water for rinsing spills.
  • Optional but helpful: a one-way check-valve bleeder or a vacuum bleeder, which makes a one-person job far less fiddly.

Setting Up the Bike and Protecting the Finish

Get the CBR300R upright and stable on a stand so the reservoir sits level and you are not chasing fluid toward the cap opening. Turn the handlebar until the front reservoir is horizontal before you touch the screws. Then drape rags over the tank, the fairing panels, the dash, and the area around the reservoir — brake fluid attacks paint and clear plastic on contact, and a drip you notice ten minutes later has usually already done its damage. Wipe any spill immediately and flush the area with water.

Bleeding the Front Brake, Step by Step

  1. Clean the reservoir cap and the area around it so grit cannot fall in, then remove the cap and the diaphragm.
  2. Draw most of the old fluid out of the reservoir with the syringe, leaving the bottom covered. Never let the reservoir run dry at any point in this job.
  3. Top up with fresh fluid from the sealed container.
  4. Push the clear tubing onto the front caliper bleeder and route the other end into the catch bottle, with the bottle positioned so you can watch the fluid move.
  5. Squeeze the front lever slowly and hold it against the grip.
  6. With the lever held, crack the bleeder about a quarter turn with the box-end wrench. Fluid and any trapped air will push out through the tube.
  7. Close the bleeder before you release the lever. Releasing first draws air back in through the nipple.
  8. Repeat the squeeze–hold–open–close cycle, checking the reservoir level every few pulls and topping it off as needed.
  9. Keep going until the fluid arriving in the tube is clean and free of bubbles, and the lever feels firm rather than springy.

If your bike happens to carry two front calipers, work through them one at a time rather than trying to do both at once. The general practice is to start with the caliper farthest from the master cylinder and finish with the closest one.

Bleeding the Rear Brake

  1. Confirm the rear reservoir is level and accessible, and protect the surrounding bodywork.
  2. Remove the cap, extract the old fluid, and refill with fresh fluid.
  3. Fit the tubing to the rear caliper bleeder and lead it to the catch bottle.
  4. Press and hold the brake pedal down.
  5. Open the bleeder a quarter turn, let the fluid and air escape, then close it fully before letting the pedal return.
  6. Repeat, watching the reservoir level, until the fluid runs clean and bubble-free and the pedal feels solid.

Finishing the Job Correctly

Snug the bleeder down firmly without overtightening — it seals on a tapered seat and does not need to be cranked. Fill the reservoir to the level marking, not above it, then reinstall the diaphragm and cap. Wipe down the caliper, the bleeder, and the master cylinder, and look closely at the bleeder and the banjo fittings for any weeping. A damp fitting after a few minutes of sitting is a leak that needs attention before the bike moves.

Testing Before You Ride

Pull the front lever and press the rear pedal several times. Both should feel firm and consistent, and neither should slowly sink while you hold steady pressure. Spin each wheel by hand to confirm the brakes are not dragging. Then, in a safe open area, test the brakes at low speed before riding normally.

When This Job Belongs in a Shop

Stop and get professional help if the lever will not firm up after several honest attempts, if it only firms up after pumping, if bubbles keep appearing no matter how long you bleed, or if fluid is seeping from the master cylinder or a caliper. On an ABS-equipped CBR300R, any event that let the reservoir run dry or that involved disconnecting the ABS unit or its lines can push air into the modulator, which generally requires a dealer-level procedure or diagnostic tool to purge. Take the bike in rather than riding it with a soft lever.

Related Shopping Categories

Shop Brake Fluid for a 2017 Honda CBR300R Motorcycle.

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Shop Brake Pads for a 2017 Honda CBR300R Motorcycle.

Shop Stands for a 2017 Honda CBR300R Motorcycle.

Shop Brake Tools for a 2017 Honda CBR300R 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.