A Rider’s Guide to Bleeding 2018 Honda CB300F ABS Brakes

Shop parts for a 2018 Honda CB300F ABS Motorcycle.

The 2018 Honda CB300F ABS uses hydraulic disc brakes at both ends, and the ABS designation means an anti-lock unit is part of the hydraulic circuit. That matters for a brake bleed: routine fluid refresh and air removal are still handled at the caliper bleeders, but if the reservoir has run dry or the ABS unit or its lines have been opened, the job can move beyond a normal garage bleed. This guide walks through a careful front and rear bleed on the CB300F ABS, with the checks that tell you when to stop and hand the bike to a shop.

When the CB300F ABS Needs a Brake Bleed

Bleeding is due when the front lever or rear pedal feels spongy, when the lever pulls closer to the grip than it used to, or when the fluid in either reservoir looks dark or cloudy. It is also required after any work that opened the hydraulic system, such as new brake lines, caliper service, or master cylinder work. Even without symptoms, brake fluid absorbs moisture over time, which lowers its boiling point and can contribute to brake fade under hard use. Many riders refresh brake fluid on a regular schedule for that reason alone.

Tools and Supplies to Have Ready

  • Fresh brake fluid of the type marked on the master cylinder reservoir cap, from a sealed container
  • A box-end wrench that fits the bleeder valve
  • Clear tubing that fits snugly over the bleeder
  • A catch bottle for used fluid
  • Rags or shop towels, plus water for rinsing spills
  • A syringe or turkey baster for removing old fluid from the reservoir
  • A screwdriver that fits the reservoir cap screws
  • Optional: a one-way check-valve bleeder or vacuum bleeder to make one-person work easier

Setting Up Safely Before You Open the System

Support the CB300F ABS securely upright on a stand so it cannot tip while you work the lever and pedal. Turn the handlebars so the front reservoir sits level before you remove the cap. Cover painted surfaces, plastics, and the instrument area with rags, because most brake fluids damage paint and plastic on contact. If a spill happens, wipe it up immediately and rinse the area with water. Keep the reservoir cap and diaphragm clean and set them where they will not pick up grit.

Bleeding the Front and Rear Hydraulic Systems

The front and rear brakes on the CB300F ABS are separate hydraulic circuits, so treat them as two jobs. Work through one circuit completely before moving to the other. On any circuit with more than one caliper, bleed one caliper at a time and finish it before moving to the next; as a general practice, begin with the caliper farthest from the master cylinder.

  1. Open the reservoir for the circuit you are bleeding and use the syringe or turkey baster to remove most of the old fluid. Do not let the reservoir run dry.
  2. Refill the reservoir with fresh fluid of the type marked on the cap, leaving room for the diaphragm.
  3. Attach the clear tubing to the bleeder valve and route the other end into the catch bottle. Make sure the tubing fits snugly so air cannot be drawn in around it.
  4. For the front brake, squeeze and hold the lever. For the rear brake, press and hold the pedal. Keep steady pressure on it.
  5. Open the bleeder about a quarter turn and let fluid and air flow out through the tube. Watch the tube, not just the reservoir.
  6. Close the bleeder before you release the lever or pedal. Releasing first can pull air back into the system.
  7. Repeat the squeeze-hold-open-close-release cycle until fresh, clean, bubble-free fluid comes through the tube. Keep topping off the reservoir throughout so it never runs low enough to draw air in.
  8. When the fluid runs clean and clear, close the bleeder snugly without overtightening, then move to the other circuit if needed.

Finishing Up and Checking for Leaks

Once both circuits are bled, fill each reservoir to the correct level marking, reinstall the diaphragm and cap, and clean any spilled fluid from the bike. Check the bleeder valves and the banjo fittings at the master cylinders and calipers for weeping or wetness. A dry fitting after a firm lever or pedal test is what you want to see. Tighten the bleeder snugly, but do not force it; overtightening can damage the seat.

Testing Before Normal Riding

The front lever and rear pedal should feel firm and consistent, not spongy, and they should not slowly sink under steady pressure. Spin each wheel to confirm the brakes are not dragging. Test the brakes at low speed in a safe area before riding normally. If the lever or pedal changes feel after the bike sits, or if either one needs pumping to come up, stop and investigate before riding.

Troubleshooting and When to See a Shop

A lever or pedal that will not firm up after several bleeding attempts, a lever that firms only after pumping, persistent air bubbles, or fluid leaking from the master cylinder or caliper are reasons to stop. On the CB300F ABS, any situation where air may have entered the ABS unit itself—such as a reservoir that ran dry, or ABS unit or line work—should go to a shop with the equipment to perform the correct ABS procedure. Do not attempt to improvise an ABS bleed sequence at home. A firm, clean, leak-free system after a low-speed test is the sign the job is complete.

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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.