Bleeding the Brakes on a 2022 KTM RC 390
Shop parts for a 2022 KTM RC 390 Motorcycle.
The 2022 KTM RC 390 runs a fully hydraulic brake setup: a front disc brake fed by a master cylinder at the lever, and a rear disc brake fed by a master cylinder at the pedal. Both circuits pass through a dual-channel ABS unit, and each circuit is independent — the lever works the front only, the pedal works the rear only. That means two separate hydraulic systems to service, each bled on its own. This guide covers refreshing the fluid and purging air from both, using ordinary hand tools, and it flags the point at which the ABS hardware puts the job beyond a home garage.
Know What You Are Working On First
Before you loosen anything, look at the two master cylinder reservoirs. The front cap sits on the handlebar-mounted reservoir; the rear cap sits on the small reservoir near the pedal. Each cap is marked with the fluid specification the system was built for. That marking is your only source of truth for fluid type — buy that fluid, and buy it in a sealed container that has never been opened. An open bottle on a shelf has already absorbed moisture, which is exactly what you are trying to remove from the system.
Because this bike carries ABS, understand the limit of a garage bleed up front. A routine flush through the caliper bleeders is fine and is what most riders need. But if the reservoir has ever run dry, or the ABS unit or its lines have been disconnected, air can be trapped inside the ABS hardware where a lever-and-bleeder routine will not reach it. That situation calls for a dealer-level procedure or diagnostic tool. Do not attempt to improvise one.
Signs the Brakes Need Bleeding
The classic symptom is a lever or pedal that feels soft or spongy, or a front lever that now comes noticeably closer to the grip than it used to. A lever that firms up only after several quick pumps is another strong indicator of air in the line. Dark, cloudy, or discolored fluid in either reservoir is a sign the fluid is past its useful life.
Bleeding is also mandatory after any work that opened the hydraulic system: new brake lines, caliper service, or master cylinder work. Beyond symptoms, brake fluid absorbs moisture from the air over time, and that moisture lowers its boiling point. A bike ridden hard with wet fluid can develop brake fade when the calipers get hot. Many riders simply refresh the fluid on a regular interval rather than waiting for a problem to appear.
Tools and Supplies to Collect
- Fresh brake fluid of the type marked on the reservoir cap, from a sealed container
- A box-end wrench that fits the bleeder valve snugly
- Clear tubing that fits tightly over the bleeder nipple
- A small catch bottle for the old fluid
- Rags or shop towels, plus a syringe or turkey baster for the reservoir
- The correct driver for the reservoir cap screws
- Optional: a one-way check-valve bleeder or a vacuum bleeder, both of which make a solo job easier
Setting Up Safely
Get the bike upright and stable on a stand so it cannot tip while you are leaning on the lever. For the front circuit, turn the handlebars until the reservoir sits level — an angled reservoir will spill. Drape rags over the tank, the fairing panels, the dash, and anything else below the reservoir, because brake fluid attacks paint and plastic on contact. If a drop lands anywhere it should not, wipe it up immediately and rinse the area with water. Keep a rag wrapped around the master cylinder and around the bleeder while you work.
The Bleeding Procedure, Step by Step
- Start with the front circuit. Remove the reservoir cap and diaphragm, then use the syringe or baster to draw most of the old fluid out of the reservoir. Do not pump the lever while the reservoir is low.
- Refill the reservoir with fresh fluid, leaving it near the full mark but not overflowing.
- Push the clear tubing onto the front caliper bleeder and route the other end into the catch bottle, with the bottle positioned so the tube runs upward from the bleeder before dropping — this helps you see bubbles.
- Squeeze the front lever and hold it firmly against the grip. Do not release it.
- With the lever held, open the bleeder about a quarter turn with the box-end wrench. Fluid and air will push out through the tube. Watch the reservoir level as it drops.
- Close the bleeder snugly before you release the lever. Releasing with the bleeder open draws air straight back into the caliper.
- Release the lever slowly, then repeat the squeeze-hold-open-close-release cycle. Top off the reservoir every few cycles so it never runs low enough to pull air in.
- Continue until the fluid coming through the tube is clean and free of bubbles, and the lever feels firm. If your bike has been fitted with a second front caliper, bleed each caliper separately, finishing with the one farthest from the master cylinder.
- Move to the rear circuit and repeat the same sequence using the pedal instead of the lever, holding the pedal down through each bleeder opening.
Finishing the Job
Give each bleeder a final snug tighten — firm, but well short of overtightening, which can damage the seat. Fill the reservoir to the correct level marking, reinstall the diaphragm and cap, and wipe away every trace of spilled fluid. Then inspect the bleeder fittings and the banjo fittings at the master cylinder and caliper for weeping or dampness.
Test Before You Ride
Both the lever and the pedal should feel firm and consistent, and neither should slowly sink while you hold steady pressure. 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.
When to Stop and Take It to a Shop
If the lever will not firm up after several full bleeding attempts, if it firms only after pumping, or if bubbles keep appearing no matter how long you bleed, stop. The same applies to fluid leaking from the master cylinder or caliper, and to any situation where air may have entered the ABS unit. Those cases need proper diagnosis, not more pumping.
Related Shopping Categories
Shop Brake Fluid for a 2022 KTM RC 390 Motorcycle.
Shop Brake Lines for a 2022 KTM RC 390 Motorcycle.
Shop Brake Pads for a 2022 KTM RC 390 Motorcycle.
Shop Stands for a 2022 KTM RC 390 Motorcycle.
Shop Brake Tools for a 2022 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.
