How to bleed and replace brake fluid on a 2018 KYMCO MXU 450i

Shop parts for a 2018 KYMCO MXU 450i ATV.

This MotoSport-exclusive guide walks you through safely flushing and bleeding the hydraulic brake system on a 2018 KYMCO MXU 450i, step by step. Follow these instructions closely, use proper PPE, and only use the recommended fluid. This procedure assumes basic mechanical skill and common hand tools; if you are unsure, seek professional service.

What you need

  • DOT 4 brake fluid (clean, unopened container)
  • Clear plastic tubing sized to caliper bleeder nipples
  • Clean catch bottle for old fluid
  • Rubber gloves, safety glasses
  • Torque wrench and metric socket set
  • Line wrench for bleeder nipples (usually 8 mm)
  • Brake bleeder pump or hand-vacuum pump OR helper for pedal/pedal-replacement method
  • Shop rags and brake-clean spray
  • Jack and stands or ramps to safely lift the ATV if needed

Model-specific notes for the 2018 KYMCO MXU 450i

  • The MXU 450i uses a hydraulic brake system that accepts DOT 4 fluid. Do not mix DOT 5 or silicone-based fluids.
  • There is no factory ABS on this model; bleeding is straightforward but the system can be sensitive to air and contamination.
  • Brake master cylinder reservoirs are exposed under the handlebar cover and on the rear master cylinder area. Remove plastic panels carefully to access reservoirs — plastic fasteners can break if pried roughly.
  • Brake lines are routed along the frame and swingarm. Inspect hoses for cracking, chafing, or soft spots while you work; replace any questionable components before finishing the job.
  • If your MXU has a parking/hand brake on the rear, exercise it during bleeding only as directed below to avoid introducing air into the parking-brake linkages.

Preparation

  • Work on a level surface. Securely chock the wheels and put the transmission in park or in gear with the engine off.
  • Clean the area around each brake reservoir cap thoroughly to prevent dirt falling into the system when opened.
  • Remove the reservoir caps and diaphragms and cover the reservoirs with clean plastic wrap to limit exposure to air while preparing.
  • Note the current fluid color and level; dark fluid indicates oxidation and the need for a full flush.

Drain & replace fluid (full system flush)

  • Start by removing old fluid from the reservoirs with a suction pump or turkey baster. Refill with fresh DOT 4 fluid to the max mark.
  • Identify bleeder nipples at each caliper. Typically there are two front calipers and one rear caliper on MXU-style ATVs; if you have dual rear calipers or a different arrangement, follow the farthest-first rule described below.
  • Attach clear tubing to the first bleeder nipple and place the other end in the catch bottle partially filled with fresh fluid to prevent air re-entry.
  • Use the farthest-first sequence: start bleeding the caliper physically farthest from the primary master cylinder then progress toward the master cylinder. On many MXU setups that will be: rear right (or rear), rear left (if applicable), then front left, then front right. Verify actual geometry on your machine and adjust order accordingly.
  • With a helper: have them slowly depress the brake lever/pedal several times and hold it down. Loosen the bleeder nipple about 1/4 turn so fluid and air flow into the tube until flow slows, then tighten the nipple. Instruct the helper to release the lever slowly. Repeat until clear, bubble-free fluid appears and the reservoir remains full. Keep the reservoir topped off to avoid drawing air into the master cylinder.
  • Using a vacuum or pressure bleeder: operate the tool per its instructions at each bleeder nipple until bubbles stop. Keep reservoir topped off and switch nipples in the farthest-first order.
  • Repeat the whole cycle for each caliper until fluid flowing from each bleeder is clean and free of bubbles, and the lever/pedal feels firm and consistent at normal travel height.
  • Periodically check the reservoir level and refill with fresh DOT 4; do not reuse old fluid or top with a different DOT rating.

Final checks and reassembly

  • Tighten all bleeder nipples to the correct snugness (check service manual torque if available; snug and then a small fraction of a turn is typical). Clean any spilled fluid immediately with water and mild detergent — brake fluid can damage paint and plastics.
  • Replace reservoir diaphragms and caps. Wipe down calipers and lines with brake cleaner to remove contamination.
  • Reinstall any plastic panels removed. Confirm all fasteners are secure and that brake lines are routed without pinching or tension through steering/suspension travel.
  • With the ATV still supported, pump the brake lever/pedal until firm. Lower to the ground and test brakes at slow speed in a safe area until you confirm full stopping performance before normal riding.

Troubleshooting

  • Spongy lever or pedal after bleeding: repeat the bleed procedure. Check for leaks at calipers, lines, master cylinder, and at hose banjo fittings.
  • Persistent bubbles: inspect for cracked hoses, loose fittings, or a leaking master cylinder seal that allows air in. Replace suspect components.
  • Contaminated fluid or rusty components: replace caliper seals or lines as needed. Internal rust may require caliper rebuild or replacement.

Maintenance tips & recommended schedule

  • Replace brake fluid every 1-2 years or sooner if contaminated; more frequent service is recommended for heavy utility or wet use.
  • Always cap reservoirs immediately after filling to minimize moisture absorption by the fluid.
  • Keep a small amount of DOT 4 on hand for top-offs, but avoid storing open bottles long-term; keep replacement fluid in a sealed, dry place.

Following this MotoSport guide will restore proper brake performance on your 2018 KYMCO MXU 450i. If you encounter internal master-cylinder problems, heavy caliper corrosion, or persistent air ingress, contact a qualified technician to avoid compromising safety.

Related Shopping Categories

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Shop Brake Lines for a 2018 KYMCO MXU 450i ATV.

Shop Brake Tools for a 2018 KYMCO MXU 450i 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.