How To Bleed 2019 Honda CB300R Motorcycle Brakes

Bleeding the Brakes on a 2019 Honda CB300R

The 2019 Honda CB300R stops on hydraulic disc brakes at both ends — a single front caliper fed by the lever-mounted master cylinder, and a rear caliper fed by the pedal master cylinder. Both circuits are serviceable in a home garage with hand tools, and both benefit from the same treatment. Honda also built this model with ABS, and most examples on the road have it, so look for the ABS badge or the toothed sensor ring at each wheel before you start. If your bike is ABS-equipped, the caliper-level bleed described here is still the correct routine for refreshing fluid; the notes near the end explain the situations that belong in a shop instead.

When a Bleed Is Actually Due

Brake fluid pulls moisture out of the air over time, and that moisture does two bad things: it lowers the fluid’s boiling point, so hard repeated braking can boil it and give you a lever that goes soft at exactly the wrong moment, and it darkens the fluid and lets corrosion start inside the calipers and master cylinder. A spongy lever, a lever that now pulls noticeably closer to the grip than it used to, a pedal with a vague or long travel, or fluid that looks dark or cloudy in the reservoir are all reasons to bleed. So is any job that opened the hydraulic system — new lines, caliper service, master cylinder work, or a bike that sat with the reservoir open. Plenty of riders simply flush on a regular interval as preventive maintenance, and on a light street bike like the CB300R that is a reasonable habit.

Gather These Before You Touch Anything

• Fresh brake fluid of the type printed on the master cylinder reservoir cap, poured from a sealed container. Do not substitute a different type, and do not use a bottle that has been open and sitting on a shelf.
• A box-end wrench that fits the bleeder valve snugly. A loose fit rounds the hex.
• Clear tubing that pushes firmly onto the bleeder nipple, plus a catch bottle to hang it in.
• Rags or shop towels, and a syringe or turkey baster for emptying the reservoir.
• The correct driver for the reservoir cap screws.
• Optional but genuinely helpful when working alone: a one-way check-valve bleeder or a vacuum bleeder.

Set Up So Nothing Gets Damaged

Get the bike upright and stable on level ground, on a stand if you have one. For the front circuit, turn the handlebar so the reservoir on the master cylinder sits level — a tilted reservoir spills the moment you crack the cap. For the rear, locate the master cylinder reservoir and confirm it is level and reachable. Then drape rags over the tank area, the plastics, the instrument cluster, and anything else below the reservoir, because brake fluid attacks paint and most plastics on contact. If a drop lands anyway, wipe it immediately and rinse the area with water rather than rubbing it in.

The Bleeding Procedure, Step by Step

1. Start with the front. Remove the reservoir cap screws, lift the cap and the rubber diaphragm out, and set them down somewhere clean where they will not pick up grit.
2. Use the syringe or baster to pull most of the old fluid out of the reservoir. Leave a shallow layer at the bottom — draining it dry lets air into the master cylinder and turns a simple flush into a much longer job.
3. Top the reservoir up with fresh fluid.
4. Slip the box-end wrench over the front caliper bleeder, then push the clear tubing onto the nipple and route the other end into the catch bottle.
5. Squeeze the front lever smoothly and hold it. Slow, steady strokes are what you want; rapid pumping whips air into the fluid.
6. While the lever is still held, open the bleeder about a quarter turn. Fluid and trapped air will push out through the tube. Watch the tube, not your hands.
7. Close the bleeder fully before you release the lever. This is the single most important habit in the whole job — release first and the system sucks air and old fluid right back in.
8. Release the lever slowly, then check the reservoir and top it off. Repeat the squeeze–open–close–release cycle, topping off every few rounds so the reservoir never runs low.
9. The first several cycles will push out dark, contaminated fluid. Keep going until what comes through the tube is clean and completely free of bubbles.
10. Move to the rear and repeat the same sequence using the pedal instead of the lever, pressing and holding it while you crack the rear bleeder. On any bike with more than one caliper on a single circuit, work the caliper farthest from the master cylinder first — on the CB300R each circuit has its own caliper, so simply finish the front before starting the rear.

Closing It Out Correctly

Snug the bleeder down firmly with the box-end wrench — tight enough to seal, not so tight that you crush the taper or strip the hex. Fill the reservoir to the level marking, but leave the small air gap the diaphragm needs; an overfilled reservoir can weep past the cap. Reinstall the diaphragm and cap and snug the screws. Rinse away any fluid residue around the calipers and reservoir with water, dry the area, then pull the lever and press the pedal a few times and look closely at the bleeder and at the banjo fittings for any weeping.

Verify the Job Before You Ride

The lever should feel firm and consistent, and it should hold steady pressure for a slow thirty-count without creeping toward the grip. The pedal should behave the same way. Spin each wheel by hand and confirm the brake is not dragging — a wheel that stops quickly on its own means something is bound up. Then take the bike to an empty lot and test at walking pace, building up gradually. If anything feels soft, long, or inconsistent, stop and diagnose rather than riding it out.

When to Stop and Take It In

If the lever will not firm up after several full rounds of bleeding, air is trapped somewhere a caliper bleeder cannot reach, and continuing to pump is not the answer. A lever that only feels good after a few pumps means air is still in the system. Bubbles that never stop can point to air being drawn past the bleeder threads or a tube that is not sealing on the nipple. Fluid weeping from the master cylinder or a caliper means a seal needs attention, not more bleeding. And on an ABS bike, if the reservoir ever ran dry, or the ABS unit or its lines were disconnected, air may have entered the modulator itself — that requires a dealer-level procedure and diagnostic tool, so have the bike transported rather than ridden. Knowing where the home job ends is part of doing it well.

Related Shopping Categories

Shop Brake Fluid for a 2019 Honda CB300R Motorcycle.

Shop Brake Lines for a 2019 Honda CB300R Motorcycle.

Shop Brake Pads for a 2019 Honda CB300R Motorcycle.

Shop Stands for a 2019 Honda CB300R Motorcycle.

Shop Brake Tools for a 2019 Honda CB300R 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.