How to Bleed & Replace Brake Fluid on a 2020 Polaris Sportsman 850 TRAIL
Shop parts for a 2020 Polaris Sportsman 850 TRAIL ATV.
This proprietary MotoSport guide walks you through safely flushing and bleeding the brake system on your 2020 Polaris Sportsman 850 TRAIL. Follow these steps carefully to restore firm lever/pedal feel, remove air, and replace old fluid with fresh DOT 4 brake fluid. If you’re not comfortable working on brakes, have a professional tech perform the service.
What you’ll need
- Fresh DOT 4 brake fluid (Polaris recommends DOT 4confirm cap marking before use)
- Clear hose/tubing that fits bleed nipples
- Catch bottle for old fluid
- Wrench set sized for caliper bleed nipples
- Turkey baster or fluid syringe (for reservoir cleaning)
- Rubber gloves, shop rags, safety glasses
- Brake bleeder pump or a helper for the manual bleed method
- Torque wrench (for reassembly where applicable)
- Container for used brake fluid for proper disposal
Important model notes for the 2020 Sportsman 850 TRAIL
- The Sportsman 850 TRAIL uses hydraulic brakes with DOT 4 fluid. Always confirm the marking on the reservoir cap before adding fluid.
- Some Sportsman models use a combined braking system (CBS) or separate front/rear circuits. Verify which circuits your unit has before bleeding: if there are two reservoirs or separate master cylinders (handlebar and foot), bleed each circuit independently.
- Avoid spilling brake fluid on painted surfaces, plastics, or rubber components — it damages finishes. Immediately wash any spills with water and a rag.
- Replace fluid every 12 to 24 months or as specified in your maintenance schedule; moisture in fluid leads to corrosion and reduced boiling point.
Prep and safety
- Work on a flat surface. Set the ATV on a stable stand or level ground and engage parking brake or put transmission in park/neutral with key off.
- Wear eye protection & gloves. Keep brake cleaner and fresh water nearby to rinse spills.
- Clean around the brake fluid reservoir cap before opening to avoid contaminating the system.
Step-by-step: Flush & replace brake fluid
- Inspect reservoir(s): remove dirt from the cap area, then remove the cap and diaphragm. Note the fluid level and color. If dark or contaminated, a full flush is recommended.
- Remove most old fluid: use a turkey baster or syringe to extract as much old fluid from the reservoir as possible without introducing air. Dispose of the fluid properly.
- Add fresh DOT 4 fluid to the reservoir to the recommended level. Keep the cap loosely on to minimize contamination while allowing the system to breathe during bleeding.
- Locate bleed nipples: on each caliper, find the bleed screw and fit a clear hose over it. Submerge the hose end in a catch bottle partially filled with clean brake fluid to prevent air re-entry.
- Bleeding order: identify which caliper is furthest from the master cylinder for that circuit and start there, finishing with the caliper closest to the master cylinder. If you have separate front and rear circuits, complete one circuit at a time. If circuits are linked by CBS, follow the sequence based on your unit’s layout — typically rear then front, or furthest to nearest per circuit.
- Manual bleed (helper method): have an assistant slowly depress the brake lever/pedal to the floor and hold it. Open the bleed nipple about a quarter turn to let fluid and air escape into the tubing until flow slows. Close the nipple, then have the assistant release the lever/pedal. Repeat until clear, bubble-free fluid flows and the lever/pedal feel is firm. Keep the reservoir topped off during the process to avoid introducing air.
- Vacuum or pressure bleeder (preferred for one-person operation): attach the bleeder to the caliper hose, apply vacuum/pressure, and open the bleed nipple to draw fluid until clear. Monitor reservoir level and refill as needed. Follow manufacturer instructions for your bleeder tool.
- Work through all bleed nipples per the chosen sequence. Each time you open a nipple, only allow fluid to run until clear, then tighten securely before the next pump or release to avoid sucking air back into the system.
- After bleeding each caliper, clean the nipple threads, torque nipples to fitment spec if available, and wipe away any fluid. Refill reservoir to the correct level and reinstall reservoir diaphragm & cap.
- Confirm pedal/lever feel: the lever/pedal should be firm and consistent with no sponginess. If spongy, repeat bleeding until all air is removed.
- Test ride slowly in a safe area, apply brakes repeatedly to confirm performance. Reinspect fluid level and any fittings for leaks after the test ride.
Post-service checks & maintenance tips
- Check for leaks at calipers, hoses, fittings, and master cylinder after bleeding and after a test ride.
- Record the service date and mileage. Replace fluid at the interval appropriate for your riding conditions — severe use may require more frequent changes.
- Inspect brake pads, caliper pistons, and rotors while working. Replace pads that are near the wear limit and service sticking pistons promptly.
- Store opened brake fluid in a sealed container and discard any fluid that has been exposed to air for extended periods, as DOT fluids absorb moisture.
- If the unit has any electronic brake components or sensors, avoid contaminating them and verify function after service.
Troubleshooting
- Persistent spongy lever/pedal: continue bleeding, check for leaks, inspect flexible hoses for internal collapse, and verify master cylinder seals are intact.
- Brake fade or poor stopping: ensure fluid is fresh DOT 4, pads and rotors are in good condition, and no air remains in system.
- Brake fluid contamination or dark fluid returns during bleeding: perform a complete flush until clear fluid exits each bleed nipple.
Following this MotoSport-exclusive procedure will help ensure your 2020 Polaris Sportsman 850 TRAIL brakes perform reliably and safely. If any step is unclear or you encounter mechanical issues beyond basic bleeding, consult a certified ATV technician.
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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.