Bleeding the Brakes on a 2020 KTM RC 390
Shop parts for a 2020 KTM RC 390 Motorcycle.
Know Your RC 390’s Brake Layout Before You Start
The 2020 RC 390 uses hydraulic disc brakes at both ends. A hand lever on the right bar pressurizes the front circuit and a foot pedal works the rear, and the two systems share nothing but fluid and a reservoir design. That independence is good news for a home mechanic: you can bleed one circuit completely, test it, and then move to the other without worrying that a mistake up front will affect the back. The front brake on this bike uses a single caliper, so you have one bleeder to work with at the wheel rather than a pair to balance.
This model also carries an ABS unit. For a routine fluid refresh — the kind of job this article covers — bleeding through the caliper bleeders is the normal approach and works fine. What you should not attempt at home is purging air that has made its way inside the ABS module itself. If the reservoir ever ran dry while the system was open, or if the ABS unit or its lines were disconnected during other work, the module can trap air that a lever-and-bleeder routine will not clear. That situation calls for a dealer or a shop with the right diagnostic equipment. There is no linked or combined braking on the RC 390, so the front lever does not activate the rear caliper and you do not have to follow a cross-circuit sequence.
Signs It’s Time, and Why It Matters
The most obvious cue is feel. A lever that has gone soft, or one that now travels noticeably closer to the grip than it used to, usually means air has entered the system or the fluid has degraded. A pedal with a mushy, vague bite tells the same story at the rear. Pop the reservoir cap and look at the fluid: fresh brake fluid is clear and pale, while fluid that has been in service for a couple of seasons turns dark, cloudy, or tea-colored. Any of those signs means it is time to flush.
There is also a maintenance reason that has nothing to do with how the brakes feel. Brake fluid is hygroscopic, meaning it pulls moisture out of the air over time, and that absorbed water lowers the fluid’s boiling point. Under hard, repeated braking — exactly the kind of use an RC 390 invites — fluid with a depressed boiling point can generate vapor in the caliper and give you a long, soft lever right when you need the brake most. Many riders simply refresh the fluid on a regular interval rather than waiting for symptoms. You should also bleed after any work that opened the hydraulic system: new lines, caliper service, or master cylinder repairs.
Tools and Supplies to Have Ready
- Fresh brake fluid of the type printed on the master cylinder reservoir cap, from a sealed container. Do not substitute a different specification, and do not use a bottle that has been open and sitting on the shelf.
- A box-end wrench that fits the bleeder valve snugly. A box-end grips the flats fully and is far less likely to round the bleeder than an open-end wrench.
- A length of clear tubing that fits tightly over the bleeder nipple, plus a catch bottle to hang it in.
- Rags or shop towels, and a syringe or turkey baster for pulling old fluid out of the reservoir.
- The correct driver for the reservoir cap screws.
- Optional but helpful: a one-way check-valve bleeder or a vacuum bleeder, either of which makes a solo job much less fiddly.
Setting Up the Bike and Protecting the Finish
Get the RC 390 upright and stable on a stand before you touch anything. For the front circuit, turn the handlebars so the reservoir on the bar sits level; a tilted reservoir will spill fluid the moment the cap comes off. Drape rags over the bodywork, the instrument cluster, and any painted surface near the reservoir and the caliper. Brake fluid attacks paint and many plastics on contact, and a single drip left to sit can leave a permanent mark. If a spill does happen, wipe it up immediately and rinse the area with water rather than waiting until the job is done.
The Bleeding Procedure, Step by Step
- Remove the reservoir cap and diaphragm. Use the syringe or baster to draw most of the old fluid out of the reservoir, but stop before the level drops far enough to expose the port at the bottom.
- Top the reservoir up with fresh fluid from your sealed container.
- Push the clear tubing onto the bleeder valve and route the other end into the catch bottle, positioned so you can watch the fluid coming through.
- Squeeze the front lever and hold it against the grip. Keep steady pressure on it for the whole step.
- With the lever held, open the bleeder about a quarter turn with the box-end wrench. Fluid and any trapped air will push out through the tube. You will feel the lever travel toward the grip as pressure releases.
- Close the bleeder fully before you let the lever go. This order is the whole trick — releasing the lever with the bleeder open draws air straight back into the caliper.
- Release the lever, then repeat steps 4 through 6. Watch the tube each time: you are looking for the fluid to change from dark and cloudy to clean and clear, with no bubbles trailing through it.
- Check the reservoir level every few pulls and top it off. Never let it run low enough to pull air in at the master cylinder, or you will be starting over.
- Once the fluid runs clean and bubble-free, hold the lever, close the bleeder snugly — firm, not cranked down hard — and remove the tubing.
- Move to the rear circuit and repeat the same sequence using the foot pedal in place of the lever. If you are ever working on a bike with two front calipers, bleed them one at a time, starting with the caliper farthest from the master cylinder.
Finishing Up and Checking for Leaks
Fill the reservoir to the level marking on the body, not above it, then reinstall the diaphragm and cap and wipe down the area. Look closely at the bleeder you just closed and at the banjo fittings at the master cylinder and caliper for any weeping or dampness. A bleeder that seeps needs a touch more snugness; a fitting that leaks needs attention before the bike goes anywhere.
Testing Before You Ride
Pull the lever and press the pedal. Both should feel firm and consistent, and neither should slowly sink while you hold steady pressure on it. Spin each wheel by hand to confirm the brakes are not dragging. Then find a safe, empty area and test the brakes at low speed before riding normally. If the lever still will not firm up after several rounds of bleeding, if it only firms up when you pump it, if bubbles keep appearing no matter how long you work, or if fluid is leaking anywhere in the system, stop and take the bike to a shop — particularly if there is any chance air reached the ABS unit.
Related Shopping Categories
Shop Brake Fluid for a 2020 KTM RC 390 Motorcycle.
Shop Brake Lines for a 2020 KTM RC 390 Motorcycle.
Shop Brake Pads for a 2020 KTM RC 390 Motorcycle.
Shop Stands for a 2020 KTM RC 390 Motorcycle.
Shop Brake Tools for a 2020 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.
