How to Bleed the Brakes on a 2019 KTM RC 390

Shop parts for a 2019 KTM RC 390 Motorcycle.

The 2019 KTM RC 390 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 a pedal-driven master cylinder, with a two-channel ABS unit sitting between them. Both circuits are serviceable at home with hand tools, and both reward a periodic flush. The one detail that separates this bike from a plain non-ABS machine is the ABS module, which holds a small pocket of fluid that a simple caliper bleed never circulates. That matters if air has ever been allowed into the system, and it shapes the advice near the end of this guide.

Understanding the Layout Before You Touch Anything

Front and rear are separate circuits on the RC 390 — the lever works the front only, the pedal works the rear only — so each side is bled independently and a fault on one does not affect the other. Each has its own reservoir: the front one is built into the master cylinder on the handlebar, and the rear is a small remote reservoir down by the pedal. Look at the cap on each before you buy anything, because the cap states the fluid specification the system was built for, and that is the only fluid you should pour in. Buy it fresh, in a sealed container, and discard whatever is left over.

Because this is an ABS-equipped machine, know the limit up front. A routine flush through the caliper bleeder valves is fine and is exactly what most riders do to refresh old fluid. But if the reservoir has run dry, if a line or the ABS unit has been removed, or if the lever went soft after a drop, air may be trapped inside the ABS module itself. Clearing that requires a dealer-level procedure or a diagnostic tool to cycle the pump. Do not improvise it.

When a Bleed Is Actually Needed

A spongy lever, a lever that now pulls noticeably closer to the grip than it used to, a pedal with a long soft travel, or fluid that looks dark or cloudy in the sight glass are all reasons to bleed. So is any job that opened the hydraulic system — new lines, caliper service, master cylinder work. Even with no symptoms, brake fluid absorbs moisture from the air over time, which lowers its boiling point and can bring on fade during hard or repeated braking. Many riders simply refresh the fluid on a regular interval as preventive maintenance rather than waiting for a soft lever.

Tools and Supplies to Gather

  • Fresh brake fluid matching the specification printed on the reservoir cap, from a sealed container
  • A box-end wrench that fits the bleeder valve snugly — a box-end grips better than an open-end and is less likely to round the hex
  • Clear tubing sized to fit tightly over the bleeder nipple
  • A small catch bottle for the old fluid
  • Rags or shop towels, plus a syringe or turkey baster for emptying the reservoir
  • The correct driver for the reservoir cap screws
  • Optional: a one-way check-valve bleeder or a vacuum bleeder, which makes a one-person job much easier

Setting Up the Bike

Get the RC 390 secure and upright on a stand so it cannot tip while you are working the lever. Turn the handlebars until the front reservoir sits level, then drape rags over the tank area, the fairing panels, the instrument cluster, and anything else below the master cylinder. Brake fluid attacks paint and plastics on contact, so wipe up any drip immediately and rinse the area with water if a spill reaches a painted surface. Lay out your tools within reach before you open anything, since you will need one hand on the lever for most of the job.

Bleeding the Front Brake

  1. Remove the reservoir cap and diaphragm, then use the syringe to draw most of the old fluid out. Leave a little in the bottom so you do not push air into the master cylinder.
  2. Refill with fresh fluid to a sensible working level and set the cap loosely back on to keep debris out.
  3. Fit the clear tubing over the front caliper bleeder valve and route the other end into the catch bottle, with the bottle positioned so you can watch fluid move.
  4. Slide the box-end wrench onto the bleeder, then squeeze the lever slowly and hold it against the grip.
  5. With the lever held, crack the bleeder about a quarter turn. Fluid and any trapped air will push out through the tube.
  6. Close the bleeder fully before you release the lever. Releasing first draws air back in through the open valve, which is the single most common mistake in this job.
  7. Repeat the squeeze–hold–open–close–release cycle, topping off the reservoir every few cycles so it never runs low enough to pull air in.
  8. Keep going until the fluid arriving in the tube is clean and free of bubbles, then finish with the lever held and the bleeder closed.

If your bike has two front calipers, bleed them one at a time and finish the caliper farthest from the master cylinder first, then move to the closer one. The general practice of starting at the farthest point keeps you from pushing old fluid back through a caliper you have already cleaned.

Bleeding the Rear Brake

  1. Open the rear reservoir, remove most of the old fluid, and top up with fresh fluid.
  2. Attach the clear tubing to the rear caliper bleeder and lead it into the catch bottle.
  3. Press and hold the pedal down, open the bleeder a quarter turn, then close it before letting the pedal return.
  4. Repeat, checking the reservoir level between cycles, until clean bubble-free fluid appears in the tube.

Finishing the Job

Tighten each bleeder snugly with the box-end wrench — firm enough to seal, never so tight that you risk damaging the caliper threads. Fill each reservoir to the level marking, reinstall the diaphragm and cap, and wipe away every trace of spilled fluid. Then inspect the bleeder valves and the banjo fittings at both calipers and at the master cylinders for weeping or dampness.

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 open area, test the brakes at low speed before riding normally — a short, gentle stop tells you more than a parking-lot guess.

When to Take It to a Shop

Stop and get professional help if the lever will not firm up after several honest bleeding attempts, if it only firms up after pumping, if bubbles keep appearing no matter how long you bleed, or if you find fluid leaking from a master cylinder or caliper. Any situation where air may have entered the ABS unit — a reservoir run dry, a disconnected line, a dropped bike — also belongs with a shop that can cycle the pump properly. Brakes are not the system to gamble on, and a second set of trained hands is cheap insurance.

Related Shopping Categories

Shop Brake Fluid for a 2019 KTM RC 390 Motorcycle.

Shop Brake Lines for a 2019 KTM RC 390 Motorcycle.

Shop Brake Pads for a 2019 KTM RC 390 Motorcycle.

Shop Stands for a 2019 KTM RC 390 Motorcycle.

Shop Brake Tools for a 2019 KTM RC 390 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.