How to Bleed & Replace Brake Fluid on a 2018 Polaris Sportsman 850

Shop parts for a 2018 Polaris Sportsman 850 ATV.

This MotoSport-exclusive service guide walks you through safely replacing and bleeding the brake fluid on a 2018 Polaris Sportsman 850 MMY. Follow every step carefully & keep the ATV stable. If you’re not confident doing brake work, have a professional technician handle it.

What you need

  • DOT 4 brake fluid (Polaris recommends DOT 4 for this model)
  • Clear plastic tubing that fits snugly over bleed nipples
  • Catch bottle for old fluid
  • Wrench set (typically 8mm-11mm for bleed nipples and banjo bolts; confirm fit)
  • Vacuum brake bleeder or hand pump OR a second person for manual pumping
  • Disposable gloves & shop rags
  • Brake-cleaner and drip pan
  • Jack stands or solid ramps to keep the ATV level and secure
  • Small funnel or syringe for filling reservoirs

Model-specific notes for the 2018 Polaris Sportsman 850

  • The 2018 Sportsman 850 uses hydraulic disc brakes front and rear with separate master reservoir locations for front (handlebar master cylinder) and rear (frame-mounted master cylinder). Identify which reservoir services which calipers before starting.
  • DOT 4 is specified for temperature performance and compatibility with components. Do not mix DOT 5 (silicone) with DOT 4.
  • ABS is not common on base Sportsman 850 models; if your machine has ABS hardware or an electronic module, consult a dealer for special bleeding procedures to purge the ABS modulator properly.
  • Brake hoses and banjo fittings on this model are routed and fastened; inspect for chafing, cracks, or fluid seepage while you have the system open.

Preparation

  • Park the ATV on a level surface, set the parking brake, and disconnect the battery negative terminal if you will be working near electrical components or performing a long service.
  • Clean the top of the reservoir caps to prevent contamination when opened. Remove cap & diaphragm. Keep the reservoir cap loosely in position so no dust falls in.
  • Determine bleed order: start with the caliper farthest from the master cylinder and finish with the nearest. For most Sportsman 850 configurations this will be: right rear, left rear (if applicable), right front, left front — verify by distance/line routing from the master cylinder.
  • Keep the fluid level in the reservoir topped up during the entire bleed to prevent air entry.

Drain & Replace (full fluid change)

  1. Raise wheels if needed to access calipers but keep ATV level when possible. Secure on stands.
  2. Use a siphon or syringe to remove old fluid from the reservoir. Don’t let new fluid contact painted surfaces; brake fluid can damage paint.
  3. Refill reservoir with fresh DOT 4 fluid to the full mark.
  4. Attach clear tubing to the bleed nipple at the caliper you’re starting with. Put the other end into a catch bottle partially filled with clean fluid to avoid drawing air back in.
  5. Crack the bleed nipple about 1/4 turn with the correct wrench. If using a vacuum pump, attach it to the tubing and pull until fluid runs clear and without bubbles, then close nipple while vacuum is held and remove pump.
  6. If using a two-person method: one person slowly depresses brake lever/pedal several times then holds it; while held, open the bleed nipple to allow fluid/air to escape until flow slows, then close the nipple before releasing the lever/pedal. Repeat until no bubbles appear and fluid is clean.
  7. After each caliper is bled, tighten the bleed nipple and wipe away any spilled fluid. Refill the reservoir to the full mark as needed before moving to the next caliper.
  8. Work through each caliper in sequence (farthest to nearest). Finish with the caliper closest to its master cylinder.
  9. Once all calipers are bled and the reservoir is at the proper level, operate the brake lever/pedal to check for firm feel. If the lever is spongy, repeat bleeding until firm.

Gravity or pressure bench bleed for initial replacement

For a full refresh, you can bench-bleed the system by filling the reservoir and opening each bleed nipple slightly, letting gravity pull fluid until no bubbles appear. This is slower but effective. Using a pressure bleeder attached to the reservoir speeds the process and helps purge air faster.

Finishing steps

  • Tighten all bleed nipples to spec snugness (do not over-torque). Clean any spilled fluid with brake-cleaner and a rag.
  • Dispose of used brake fluid per local hazardous-waste rules.
  • Reinstall reservoir cap and diaphragm. Reconnect battery negative if disconnected.
  • Lower the ATV, test brakes at low speed in a safe area to confirm firm operation before normal riding.
  • Recheck fluid level after a short test ride and inspect for leaks at hoses, banjo bolts, and calipers.

Warnings & best practices

  • Never reuse old brake fluid. Contaminated fluid reduces braking performance and can damage components.
  • Keep brake fluid away from painted surfaces; it will strip paint. Rinse immediately with water if contact occurs.
  • If your Sportsman 850 has an ABS unit or electronic brake-assist components, avoid aggressive vacuum methods without confirming procedures for the module. When in doubt, use a professional shop or dealer procedure.
  • After bleeding, a few firm lever/pedal applications before riding are normal. If sponginess persists, rebleed and inspect for leaks or a failing master cylinder.

Quick troubleshooting

  • Persistent bubbles: reservoir being emptied between cycles — keep topped up.
  • Soft lever after bleeding: trapped air remains; repeat sequence and ensure bleed nipples are closed before releasing lever.
  • Leaks at banjo fittings: replace crush washers and torque fittings properly; inspect for thread damage.
  • Brake drag after bleeding: caliper pistons may need to be inspected for corrosion or stuck slide pins; service as needed.

Perform this service periodically as part of brake maintenance or whenever contamination or moisture ingress is suspected. Proper brake-fluid replacement keeps your 2018 Polaris Sportsman 850 stopping reliably and safely.

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Shop Brake Tools for a 2018 Polaris Sportsman 850 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.