Bleeding the Brakes on a 2017 Kawasaki Ninja 300

Shop parts for a 2017 Kawasaki EX300 - Ninja 300 Motorcycle.

First, Confirm What Your EX300 Is Working With

The 2017 Kawasaki Ninja 300 uses hydraulic disc brakes at both ends, so this job covers two separate systems: the front circuit fed by the lever on the right handlebar, and the rear circuit fed by the pedal on the right footpeg bracket. Each has its own master cylinder, its own reservoir, and its own bleeder at the caliper, and each gets bled on its own. The two circuits are independent on this bike – the front lever does not operate the rear brake and the pedal does not operate the front – so there is no linked-brake sequence to worry about here.

ABS was offered as an option on this model year, so take a moment to identify your own machine before you start. An ABS-equipped Ninja 300 will have a toothed ring and a wheel speed sensor at the wheels, and the dash will show an ABS indicator when the key is first turned on. If your bike has no such hardware, it is the non-ABS version and the procedure below applies exactly as written. If it does have ABS, the same caliper-level bleeding still works fine for a routine fluid refresh, but there is an important limit covered further down.

Why Brake Fluid Needs Replacing, Not Just Topping Off

Brake fluid is hygroscopic, meaning it pulls moisture out of the air over time, and that moisture does two harmful things. It lowers the fluid's boiling point, so hard, repeated braking can generate vapor in the caliper and give you a lever that goes soft exactly when you need it most. It also darkens the fluid and can accelerate wear inside the master cylinder and caliper seals. That is why many riders treat a bleed as scheduled maintenance rather than a repair.

On top of the calendar, bleed the Ninja 300 whenever the lever or pedal feels spongy, when the lever creeps closer to the grip than it used to, when the fluid in either reservoir looks dark or cloudy, or after any work that opened the hydraulic system – new lines, a caliper rebuild, or master cylinder service. A lever that firms up only after two or three quick pumps is a classic sign that air is in the circuit.

Tools and Supplies to Have on the Bench

  • Fresh brake fluid of the type printed on the master cylinder reservoir cap, from a sealed container that has not been sitting open
  • A box-end wrench that fits the bleeder valve snugly – a box-end grips the flats far better than an open-end and is much less likely to round the bleeder
  • A length of clear tubing that fits tightly over the bleeder nipple
  • A small catch bottle to hang the tubing into
  • Rags or shop towels, plus a spray bottle of water for rinsing spills
  • A syringe or turkey baster for pulling old fluid out of the reservoir
  • The correct driver for the reservoir cap screws

A one-way check-valve bleeder or a vacuum bleeder makes the job much easier when you are working alone, since you no longer have to coordinate the lever and the bleeder valve at the same time.

Setting Up So You Do Not Damage the Finish

Get the bike securely upright on a stand so the reservoirs sit level and you can reach both calipers comfortably. Turn the handlebars until the front reservoir is as flat as it will get before you remove the cap. Brake fluid attacks paint and most plastics on contact, so drape rags over the front fender, the fairing panels, the dash area, and the rear tail section before you open anything. If a drop lands on a painted surface, wipe it up immediately and rinse the area with water rather than rubbing it in.

Bleeding the Front Brake, Step by Step

  1. Wipe the reservoir cap and the area around it clean so grit cannot fall in, then remove the cap and the diaphragm.
  2. Use the syringe or baster to draw most of the old fluid out of the reservoir. Leave enough at the bottom that you are not pulling air into the master cylinder port.
  3. Refill with fresh fluid from the sealed container, keeping the level well up the sight glass or above the lower mark.
  4. Slide the clear tubing over the front caliper bleeder and route the other end into the catch bottle, with the bottle positioned so the tubing runs upward then down – that shape helps you see bubbles travel.
  5. Fit the box-end wrench onto the bleeder.
  6. Squeeze the front lever firmly and hold it against the grip. Do not release it yet.
  7. Open the bleeder about a quarter turn. Fluid and any trapped air will push out through the tubing, and the lever will travel toward the grip.
  8. Close the bleeder snugly before you let the lever go. Releasing with the bleeder open is the fastest way to suck air back into the caliper.
  9. Release the lever slowly and let it return on its own.
  10. Check the reservoir and top it off. Repeat the squeeze, open, close, release cycle until the fluid coming through the tubing runs clean and clear with no bubbles, and the lever feels firm.

If your bike has more than one front caliper, bleed them one at a time and finish one completely before moving to the next. As a general habit, start with the caliper farthest from the master cylinder in terms of hydraulic path, then work toward the closest.

Bleeding the Rear Brake

  1. Clean around the rear reservoir cap, then open it and remove most of the old fluid.
  2. Top up with fresh fluid.
  3. Attach the clear tubing to the rear caliper bleeder and run it to the catch bottle.
  4. Press and hold the brake pedal down.
  5. Open the bleeder a quarter turn, let fluid and air escape, then close it snugly while the pedal is still held.
  6. Release the pedal, top off the reservoir, and repeat until the fluid runs clean and bubble-free and the pedal feels solid underfoot.

Finishing Up: Levels, Tightness, and Leak Checks

Once both circuits are bled, set the fluid in each reservoir to the level marked on the housing – not overfull, since fluid expands and needs headroom. Reinstall the diaphragm and cap and snug the screws down evenly. Give each bleeder a final snug turn with the box-end wrench; it needs to be tight enough to seal and no more, because overtightening can crush the seat and create a leak. Wipe down every surface you touched, rinse any suspect areas with water, and then look closely at the bleeder valves and the banjo fittings at both master cylinders and calipers for weeping or wetness.

Confirming the Job Before You Ride

Pull the front lever and press the rear pedal separately. Each should feel firm and consistent, and neither should slowly sink while you hold steady pressure on it. Spin the front and rear wheels by hand and confirm they turn freely without the pads dragging. Then, in a safe, empty area at low speed, test each brake on its own before riding normally.

When This Job Belongs in a Shop

If the lever or pedal will not firm up after several full bleeding cycles, if it only firms up after pumping, if bubbles keep appearing no matter how long you bleed, or if you find fluid weeping from a master cylinder or caliper, stop and have the bike inspected. On an ABS-equipped Ninja 300, a routine caliper bleed is fine, but if the reservoir ever ran dry, or the ABS unit or its lines were disconnected, air may be trapped inside the ABS unit itself. That requires a dealer-level procedure or diagnostic tool, and it is not a home-garage job.

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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.