How to Bleed and Replace Brake Fluid on a 2018 KYMCO MXU 150X

Shop parts for a 2018 KYMCO MXU 150X ATV.

This MotoSport-exclusive guide walks you through safe, repeatable steps to fully replace and bleed the brake fluid on a 2018 KYMCO MXU 150X. Procedures below assume the MXU 150X stock hydraulic brake system is intact & that you will use the correct DOT fluid specified on your vehicle reservoir cap or in the owner's manual. If you're unsure which DOT rating to use, verify the marking on the master cylinder cap before starting.

Tools & supplies

  • Correct DOT brake fluid (use only the DOT rating shown on the master cylinder reservoir)
  • Brake bleeder kit (vacuum pump or clear hose & bottle)
  • Small open wrench set for bleeder screws (inspect screw sizes on your MXU)
  • Turkey baster or syringe (for removing old fluid from reservoir)
  • Clean lint-free rags and nitrile gloves
  • Catch container & used fluid disposal bag
  • Wheel chocks, ATV stand or ramps, jack stands rated for ATVs
  • Brake cleaner, penetrating oil for corroded fittings
  • Rubber caps or new bleeder screw caps, thread locker if specified by manual

Important notes for MXU 150X owners

  • The MXU 150X uses a compact master cylinder – reservoir fluid capacity is small; don't let the reservoir run dry during bleeding to avoid introducing air.
  • Some MXU 150X components — plastic reservoir & fittings — age brittlely; handle the cap, diaphragm, and plastic lines carefully to avoid cracking when removing.
  • Bleeder screws on the MXU 150X can be small and prone to rounding if incorrect tool size is used. Use the correct wrench and keep some penetrating oil handy for seized screws.
  • Confirm whether your unit has separate front master cylinder vs. linked system. The bleed sequence described below assumes a single master cylinder feeding multiple calipers; adjust if your unit has two separate circuits (consult your manual).
  • Dispose of old brake fluid properly — it is toxic and will damage paint and plastics.

Preparation

  • Work on a level surface with engine off and key removed.
  • Chock the wheels and lift the ATV so wheels can turn freely; secure on stands.
  • Clean the reservoir cap area to prevent contamination. Remove cap, diaphragm, and inspect fluid color — dark or contaminated fluid indicates an immediate full flush is required.
  • Siphon or turkey-baste out as much old fluid from the reservoir as possible without letting the reservoir go dry.
  • Top reservoir with fresh DOT fluid to the recommended level.

Bleeding strategy

Use the "furthest-from-master" rule: bleed the caliper farthest from the master cylinder first, then work toward the closest. On most MXU layouts this will be: rear opposite side first, then the other rear, then front sides. If your MXU 150X has a different plumbing layout, follow the routing to identify the furthest outlet.

Step-by-step bleed (manual pump + assistant)

  1. Attach a clear hose to the caliper bleeder screw and route it into a catch bottle partially filled with fresh fluid to prevent air drawback.
  2. Ask an assistant to sit on the seat and slowly pump the brake lever/pedal 3-5 times and then hold firm pressure.
  3. With pressure held, open the bleeder screw about a quarter-turn until fluid & bubbles flow into the hose, then close the screw before the assistant releases pressure. Repeat until no air bubbles appear.
  4. Top the reservoir after each caliper cycle to prevent it from running dry.
  5. Move to the next caliper (next furthest) and repeat the pump/hold/open/close cycle until all four corners are clear of air and the lever/pedal feels firm and consistent.
  6. Finish by tightening bleeder screws to a snug fit. If your manual lists torque values, use them; if not, tighten to a firm feel without over-torquing to avoid rounding or damaging threads.

Step-by-step bleed (vacuum or pressure bleeder)

  • Connect the vacuum bleeder to the caliper bleeder fitting or pressurize the master cylinder reservoir with the pressure kit per the kit instructions.
  • Open the bleeder screw and run fluid until clear, air-free fluid flows. Keep reservoir topped with fresh fluid.
  • Close the bleeder, move to the next caliper, and repeat in the proper sequence.

After bleeding

  • Confirm lever/pedal firmness with ATV on stands and with one wheel at a time rotated to verify braking action is even.
  • Inspect all connections for leaks; recheck bleeder screw tightness after a short test ride.
  • Properly dispose of old fluid; wash any spilled fluid off painted surfaces with water and brake cleaner as appropriate.
  • Reset reservoir cap and diaphragm securely; some MXU 150X owners find replacing the rubber diaphragm if cracked prevents future contamination.

Troubleshooting

  • Spongy lever after bleeding: recheck for air & verify reservoir never ran dry during process; re-bleed if necessary.
  • Bleeder screw spins or is rounded: stop, use correct-size wrench or extract and replace the bleeder screw to avoid future leaks.
  • Persistent pedal travel: inspect master cylinder seals and caliper piston condition. If seals are worn, a master cylinder or caliper rebuild may be required.
  • Seized caliper piston: use brake cleaner and careful back-pushing techniques or remove the caliper for rebuild if it won't move.

Maintenance tips specific to the MXU 150X

  • Bleed interval: replace brake fluid every 1-2 years or sooner if fluid appears dark or contaminated; MXU 150X's small reservoir means moisture contamination can make feel degrade faster.
  • Inspect plastic reservoir for hairline cracks during each service; replace early to avoid unexpected leaks.
  • When replacing brake pads or caliper hardware, always re-bleed to remove any introduced air and confirm proper piston retraction sequence.
  • Keep an OEM or quality replacement bleeder screw and small replacement rubber caps in your tool kit; they're inexpensive insurance on older MXU units.

If you prefer to buy parts, seals, replacement bleeder screws, or the correct DOT fluid for your 2018 KYMCO MXU 150X now, visit the MotoSport parts page for your model to ensure fitment and OEM-quality gear.

Related Shopping Categories

Shop Brake Fluid for a 2018 KYMCO MXU 150X ATV.

Shop Brake Bleeders for a 2018 KYMCO MXU 150X ATV.

Shop Brake Pads for a 2018 KYMCO MXU 150X ATV.

Shop Brake Lines for a 2018 KYMCO MXU 150X ATV.

Shop Brake Tools for a 2018 KYMCO MXU 150X ATV.

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.