How to Bleed and Replace Brake Fluid on a 2018 Polaris Sportsman 850 SP
Shop parts for a 2018 Polaris Sportsman 850 SP ATV.
This MotoSport guide walks you through safely flushing and bleeding the brake system on a 2018 Polaris Sportsman 850 SP, what to watch for on this MMY model, tools and supplies, and best practices to leave the system clean, air-free, and reliable.
What you need to know about the 2018 Polaris Sportsman 850 SP
- The Sportsman 850 SP uses a hydraulic disc brake system with a master cylinder and remote reservoirs. Check the master cylinder cap for the specified DOT fluid type; many Polaris models use DOT 4, but confirm on your machine before purchasing fluid.
- This model does not use an ABS pump. Brakes are mechanical/hydraulic and susceptible to contamination from water or incorrect fluid; change fluid if it looks dark, milky, or contaminated.
- Brake lines are routed close to the frame and suspension; inspect lines and hoses for wear, chafing, leaks, and secure mounting before and after service.
- Have a service manual or OEM torque specs available for caliper mounting and banjo bolt torque when reassemblingMotoSport recommends following Polaris torque values exactly.
Tools & supplies
- Correct DOT brake fluid (confirm on master cylinder cap).
- Clear plastic tubing sized to the bleeder nipple plus a catch bottle.
- Wrenches for bleeder nipples (typically 8mm or 10mm) and banjo bolts per model.
- Turkey baster or fluid syringe to remove old fluid from the reservoir.
- Clean shop rags, brake cleaner, disposable gloves, eye protection.
- Optional: vacuum bleeder, pressure bleeder, or two-person helper.
- Jack or ramps and stands to safely raise/stabilize the ATV if needed.
Safety and prep
- Work on a flat, stable surface with the engine off and key removed. Chock wheels to prevent movement.
- Protect painted surfaces from brake fluid; it strips paint. Cover surrounding areas with rags or plastic.
- Wear gloves and eye protection. Dispose of old fluid per local regulations.
- Do not reuse DOT brake fluid once it has been opened for extended periods; buy a fresh bottle.
Step-by-step: Full fluid replacement and bleed
Procedure covers reservoir, calipers, and final system bleeding. Perform on one axle at a time (rear first is common), finishing at the wheel farthest from the master cylinder.
- Locate the master cylinder/reservoir. Clean the cap area thoroughly to prevent contamination, then remove the cap and diaphragm.
- Use a turkey baster or syringe to remove as much old fluid from the reservoir as possible. Dispose of removed fluid properly.
- Top the reservoir with fresh DOT fluid to the fill line. Keep the cap off during the process but don't let the reservoir run dry at any time.
- Start with the caliper farthest from the master cylinder (typically rear right on many Polaris routing) and work toward the master cylinder, ending with the nearest caliper. If unsure of routing, trace the hard line from the reservoir to confirm sequence.
- Attach clear tubing to the bleeder nipple and place the other end into a catch bottle partially filled with clean brake fluid to prevent air from being sucked back in.
- Open the bleeder nipple ~1/4 turn. Have a helper slowly depress and hold the brake lever/pedal; then have them release. Each squeeze pushes fluid and air out. Repeat until clear fluid with no air bubbles appears in the tubing. Keep reservoir topped up during the process.
- If you're working alone, use a vacuum bleeder or pressure bleeder to pull fluid through each caliper. With a vacuum unit, attach the hose to the bleeder nipple, open the nipple, and pump until clean fluid flows. For a pressure bleeder, pressurize the master cylinder reservoir per tool instructions and open bleeders in sequence.
- Tighten bleeder nipples to spec once air-free fluid flows. Wipe any spills immediately and recheck fluid level in the reservoir.
- Repeat bleeding at each caliper in sequence until every location yields clear, bubble-free fluid and the brake lever/pedal feels firm.
- When finished, top reservoir to the correct level, reinstall the diaphragm and cap, clean any spilled fluid, and test lever/pedal firmness with the ATV stationary.
- Road-test cautiously at low speed to confirm braking performance, then recheck reservoir level and inspect for leaks.
Tips for reliable results
- Never let the reservoir run dry during bleeding – doing so reintroduces air into the system and forces you to repeat the procedure.
- Replace rubber seals, hoses, or worn caliper components if you find leaks or cracked lines during inspection.
- Use short, firm pedal/lever strokes — long, fast strokes tend to pull air into the system at the master cylinder.
- If fluid looks milky, it indicates water contamination — replace and bleed the system immediately; contaminated fluid lowers boiling point and compromises stopping power.
- After bleeding, verify torque on any removed banjo bolts and clean the area with brake cleaner. Follow Polaris torque specs from the service manual.
Common issues specific to the Sportsman 850 SP
- Reservoir contamination: riding in wet, muddy conditions can contaminate the reservoir cap area. Clean before opening and replace the diaphragm or cap if degraded.
- Line routing and chafe: suspension movement can pinch lines; inspect clamps and replace worn sections. A worn hose can leak internally and cause spongy brakes.
- Brake lever feel: if you still have a soft lever after bleeding, recheck for master cylinder internal seal leaks or caliper piston issues — both require repair or overhaul.
Maintenance schedule
- Inspect brake fluid color and level every 3 months or after heavy use. Replace fluid every 1-2 years or sooner if contaminated or discolored.
- Inspect lines, fittings, and caliper hardware annually or after rough trail use.
Final checks
- Confirm there are no leaks, the lever/pedal is firm, and brake performance is consistent.
- Perform a low-speed test ride and re-inspect for leaks and fluid level.
For model-specific parts, replacement seals, and service kits for the 2018 Polaris Sportsman 850 SP, MotoSport stocks OEM-compatible components to complete your brake service and keep your machine stopping safely.
Related Shopping Categories
Shop Brake Fluid for a 2018 Polaris Sportsman 850 SP ATV.
Shop Brake Bleeders for a 2018 Polaris Sportsman 850 SP ATV.
Shop Brake Pads for a 2018 Polaris Sportsman 850 SP ATV.
Shop Brake Lines for a 2018 Polaris Sportsman 850 SP ATV.
Shop Brake Tools for a 2018 Polaris Sportsman 850 SP 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.