How to Bleed and Replace Brake Fluid on a 2021 Kubota RTV520

Shop parts for a 2021 Kubota RTV520 ATV.

This guide from MotoSport covers a complete, safe, step-by-step procedure to replace and properly bleed the brake system on a 2021 Kubota RTV520. It includes tools, safety notes specific to the RTV520, recommended fluids & seals, and troubleshooting tips so you can restore firm, reliable brakes.

What you need

  • DOT 4 brake fluid (use factory-specified fluid if different; consult your owner’s manual)
  • Brake bleeder wrench or correct-sized open-end wrench
  • Clear tubing that fits over bleeder nipples
  • Catch bottle or jar, funnel, clean rags
  • Hand-operated vacuum bleeder or pressure bleeder (recommended for fastest, cleanest job)
  • Jack and stands or ramps to lift and support the RTV520 safely
  • Torque wrench and basic hand tools
  • Brake parts cleaner, disposable gloves, eye protection

Model-specific notes for the 2021 Kubota RTV520

  • The brake fluid reservoir is located under the hood near the master cylinder; it is a small plastic reservoir with MIN/MAX marks. Keep the cap and reservoir area clean to avoid contamination.
  • The RTV520 typically uses DOT 4 compatible fluid; do not mix with silicone-based fluids. If the RTV520 has ABS or traction-assist hardware on a variant, follow the ABS-specific bleed sequence from the manual or use a pressure bleeder to ensure proper purge.
  • Parking brake cables and rear drum/caliper access may require removing cargo bed panels on select trims. Allow extra time to access rear bleeder nipples.
  • Rust, stuck caliper pistons, or collapsed hoses are common wear items on older RTVs — inspect all rubber lines, fittings, calipers, and wheel cylinders while you have the wheels off.
  • Always replace rubber reservoir cap grommet or seal if damaged; contamination here will ruin new fluid quickly.

Safety first

  • Work on a level surface with the engine off, key removed, and parking brake engaged where safe.
  • Wear gloves and eye protection. Brake fluid damages paint; wipe spills immediately and rinse with water.
  • Support the RTV520 on stands or ramps; never rely on a jack alone when working under the vehicle.

Preparation

  1. Clean the master cylinder reservoir cap and area to prevent contamination.
  2. Remove enough old fluid from the reservoir using a syringe or turkey baster so the fluid level is near the MIN mark but not empty.
  3. Top off with fresh DOT 4 fluid to the MAX line. Keep the cap loosely in place to minimize air entry while working.
  4. Loosen lug nuts, raise the RTV520, and remove wheels to access bleeder nipples on each caliper or wheel cylinder.
  5. Identify bleed sequence: generally right rear, left rear, right front, left front on many UTVs. If in doubt, follow the Kubota service manual sequence for the RTV520 or use the longest line/most remote caliper first (often right rear).

Bleeding methods

Method A - Two-person manual bleed

  1. One person sits in the cab and presses the brake pedal; the other opens and closes bleeder nipples.
  2. Attach clear tubing to the bleeder nipple and route into a catch bottle partially filled with old fluid (prevents air re-entry).
  3. Have the helper pump the pedal 3–5 times and hold firm. Open the bleeder nipple about a half-turn to let fluid and air out, then close it before the pedal is released. Repeat until clear fluid with no bubbles appears, then move to the next wheel.
  4. Keep reservoir topped between cycles to avoid drawing air into the master cylinder.

Method B - Vacuum bleeder (recommended for one-person, cleaner job)

  1. Attach the vacuum bleeder to the bleeder nipple with tubing and apply vacuum per the tool instructions.
  2. Open the bleeder and allow fluid to be drawn out until clear, bubble-free fluid appears. Close the bleeder, release vacuum, then move on.
  3. Keep reservoir topped to prevent air entry.

Method C - Pressure bleeder (best for ABS or stubborn air)

  1. Use a pressure bleeder on the master cylinder reservoir per tool instructions. Pressurize the system to the specified safe pressure (usually low psi). Open bleeders in sequence until clear fluid runs out and no bubbles are present.
  2. Pressure bleeding is fastest and helps purge ABS modulator cavities when applicable.

Bleeding tips & details

  • Always bleed from the caliper/wheel cylinder bleeder nipple, not the master cylinder.
  • Work one wheel at a time to keep the system organized. Tighten bleeder nipples to the specified torque in the manual after each wheel (snug is usually 8–15 ft-lb depending on nipple size; consult the manual for exact spec).
  • If you get a spongy pedal after all wheels are bled, bleed the master cylinder (bench bleed if removed) and repeat the wheel sequence.
  • If you suspect air in an ABS unit, cycle the ABS pump per factory procedure or use a diagnostic/bleed tool for ABS units.
  • Dispose of old brake fluid per local hazardous waste regulations.

Final checks

  1. With all wheels bled and nipples tightened, ensure reservoir is topped to MAX and cap is sealed.
  2. Reinstall wheels, torque lug nuts to the specified value for the RTV520, lower the vehicle, and torque again to spec.
  3. Start the RTV520, press the brake pedal to confirm firm pedal travel. Park on a safe slope and test the parking brake function.
  4. Perform a low-speed road test in a safe area to check braking effectiveness and pedal feel.

Troubleshooting

  • Persistent soft pedal: likely air still in the system, leaking line, or failing master cylinder. Recheck hose and fitting integrity and repeat bleeding.
  • Leaking bleeder nipple or caliper seal: replace the damaged part and bleed again.
  • Collapsed rubber hoses or swollen lines: replace rubber brake hoses as necessary; don’t reuse damaged hoses.

Routine maintenance recommendations

  • Replace brake fluid every 1–2 years depending on use and exposure to moisture. Heavy-duty or wet conditions call for more frequent changes.
  • Inspect brake pads, rotors, drums, and hardware whenever you change fluid. Replace worn pads and hardware proactively to prevent damage.
  • Keep the reservoir cap and seal in good condition to prevent contamination and premature fluid degradation.

Follow these steps and model-specific precautions to safely replace and bleed the brake fluid on your 2021 Kubota RTV520. If you encounter unusual symptoms, or if the vehicle has ABS/advanced electronics and bleeding methods above don’t restore pedal feel, contact a professional technician or your Kubota dealer for service.

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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.