How to bleed and replace brake fluid on a 2021 CFMOTO CFORCE 400

Shop parts for a 2021 CFMOTO CFORCE 400 ATV.

This MotoSport guide gives step-by-step, model-specific instructions for changing and bleeding the brake fluid on a 2021 CFMOTO CFORCE 400. Follow these procedures carefully to restore firm braking, avoid contamination, and protect the ATV's finish and seals.

What you need

  • DOT 4 brake fluid (MotoSport recommends DOT 4 for CFORCE 400 systems). Do not use DOT 5 silicone fluid.
  • Clear tubing that fits the bleeder nipple snugly
  • Catch bottle and small funnel
  • Spanners or wrenches sized for master cylinder reservoir cap and bleeder nipples (typically 8-10 mm)
  • Vacuum bleeder or pressure bleeder (recommended) or a helper for manual pump-and-hold method
  • Clean rags, isopropyl alcohol, nitrile gloves, and safety glasses
  • Small syringe or turkey baster for removing old fluid from reservoir
  • Jack or stand to safely lift wheels if needed

Notes specific to the 2021 CFMOTO CFORCE 400

  • The CFORCE 400 uses a conventional hydraulic system with a front master cylinder and a separate rear master cylinder/combination valve depending on configuration. Inspect both reservoirs; some models have the rear reservoir under the seat or a side cover.
  • Brake reservoir caps are plastic; avoid overtightening and clean the area thoroughly before opening to prevent contamination.
  • The ATV typically does not have ABS. If your model has factory safety options, confirm electrical/ABS components won't be exposed to fluid.
  • Brake lines are routed near plastic panels. Protect paint and plastic from spilled fluid & wipe any contact immediately with isopropyl alcohol.

Preparation

  1. Park the ATV on level ground and secure it with the parking brake on and engine off. Use a stand or jack to place wheels at a comfortable height if desired.
  2. Clean around each reservoir cap thoroughly to keep dirt out of the system.
  3. Put on gloves and eye protection. Open the master cylinder reservoir cap and remove the diaphragm/foam pad so you can access fluid but replace it as designed during reassembly.
  4. Use a syringe or turkey baster to remove as much old fluid from the reservoir as possible without introducing air. Dispose of fluid properly.

Bleeding procedure — preferred MotoSport method (pressure or vacuum bleeder)

  1. Top the reservoir with fresh DOT 4 fluid to the max mark.
  2. Attach clear tubing to the bleeder nipple on the caliper or wheel cylinder and submerge the far end in a small bottle partially filled with fresh fluid to prevent drawing air back in.
  3. Attach a pressure bleeder to the reservoir or a vacuum pump to the caliper bleeder as appropriate. Pressurize gently per the tool instructions — do not exceed manufacturer pressure recommendations (typically under 15 psi).
  4. Open the bleeder nipple one quarter to one half turn. Allow fluid and air to flow until clear, bubble-free fluid appears in the tubing. Keep reservoir level topped off during the entire process to prevent air ingestion.
  5. Close the bleeder nipple, then release pressure or vacuum. Wipe the nipple and repeat for the other side if dual caliper front system exists. For rear brake, locate the rear bleeder and repeat the same sequence.
  6. Cycle the brake lever/pedal slowly several times after each caliper is bled to seat seals and expel any remaining microbubbles. Recheck reservoir and top to the max mark.

Alternative — two-person manual pump-and-hold method

  1. One person pumps the brake lever or pedal slowly while the second opens the bleeder nipple briefly as the lever is held down to allow fluid and air out, then closes the nipple before the lever/pedal is released.
  2. Repeat until clear fluid flows and the lever feels firm. Keep the reservoir topped off at all times.

Final steps

  1. Once all calipers/wheel cylinders are bled, confirm reservoir fluid is at the correct level and reinstall diaphragm/foam and cap. Torque the cap snug but do not overtighten.
  2. Clean any spilled fluid with isopropyl alcohol. Inspect lines, fittings, and hose routing around the frame and plastic panels for leaks or chafing.
  3. Operate the brakes at low speed in a safe area to confirm firm pedal/lever feel before riding normally. Expect a short bedding-in period for optimal braking performance.
  4. Properly dispose of old brake fluid per local regulations. Record the service date and fluid type in your maintenance log.

Helpful tips & cautions

  • Never mix DOT 4 and DOT 5 silicone fluid. DOT 3 can be mixed with DOT 4 but DOT 4 is recommended for higher boiling point and better performance under load.
  • Keep the reservoir capped when not actively bleeding to avoid absorbing moisture; brake fluid is hygroscopic and absorbs water from the air.
  • If the brake lever remains spongy after thorough bleeding, inspect caliper pistons for corrosion or seized hardware, and check the master cylinder seals & internal bore for wear. MotoSport recommends replacing worn seals or remanufactured master cylinders rather than continuing to bleed an internally leaking unit.
  • Replace rubber hoses showing swelling, cracks, or soft spots. Old hoses can expand under pressure and cause soft brakes.
  • If the CFORCE 400 has a combination front/rear proportioning device, ensure it is bled according to the model configuration — bleed the farthest caliper first, then the nearest.

Perform brake fluid replacement every two years or sooner if the fluid looks dark or contaminated. Proper bleeding restores brake responsiveness and ensures safe operation of your 2021 CFMOTO CFORCE 400.

Related Shopping Categories

Shop Brake Fluid for a 2021 CFMOTO CFORCE 400 ATV.

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Shop Brake Pads for a 2021 CFMOTO CFORCE 400 ATV.

Shop Brake Lines for a 2021 CFMOTO CFORCE 400 ATV.

Shop Brake Tools for a 2021 CFMOTO CFORCE 400 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.