How to bleed and replace brake fluid on a 2008 Yamaha BigBear 400 4X4 – MotoSport shop guide

Shop parts for a 2008 Yamaha BigBear 400 4X4 ATV.

This MotoSport procedure walks you through safely replacing and bleeding the hydraulic brake fluid on a 2008 Yamaha BigBear 400 4X4. Follow each step deliberately, use clean tools and fresh brake fluid, and work in a clean, well-ventilated area. Brake work affects safety — if you are not confident, have a qualified mechanic perform the job.

What you will need

  • DOT 4 brake fluid (Yamaha recommends DOT 4 for many models — verify label on master cylinder cap)
  • Clear plastic tubing to fit bleed nipples
  • Small clear catch bottle (to monitor bubbles)
  • Wrench set (for bleed nipples and caliper fittings)
  • Vacuum bleeder or hand pump (optional but speeds job)
  • Turkey baster or fluid syringe (to remove old fluid from reservoir)
  • Clean lint-free rags and brake cleaner
  • Rubber gloves and eye protection
  • Jack or stands to safely lift the ATV, wheel chocks

Safety and model notes specific to the 2008 BigBear 400

  • The BigBear 400 uses sealed hydraulic calipers and a reservoir on the handlebar master cylinder for the front brake. There is a separate rear master cylinder/reservoir for the rear brake. Confirm which reservoir feeds which brake before starting.
  • Use only DOT 4 fluid unless the master cylinder cap explicitly states another type. Mixing fluids or using mineral oil will damage seals.
  • Keep fluid off painted surfaces — brake fluid will strip paint. Wipe any spills immediately with water and a rag.
  • There is no ABS on this model, but check for worn hoses or leaks around banjo fittings common on older BigBear units.
  • Brake fluid should be replaced every two years or sooner if contaminated or dark. Inspect caliper seals, hoses, and pads while you have the system open.

Preparation

  • Park ATV on level ground, engage park/parking brake, block wheels.
  • Lift and support the bike so wheels can spin freely if required for caliper access.
  • Clean around master cylinder reservoir caps to prevent contamination when opened.
  • Remove the master cylinder reservoir cap(s) and diaphragm. Use a turkey baster to remove old fluid from the reservoir down to just above the inlet level, leaving a small amount to avoid drawing air into the lines.
  • Refill reservoir with fresh DOT 4 fluid to the cold full mark or safe level. Do not overfill.

Bleeding order

Work from the caliper farthest from each master cylinder toward the closest. For most BigBear 4X4 setups that means:

  • Rear brake: farthest rear caliper first, then nearer caliper (if dual calipers exist).
  • Front brake: farthest front caliper first, then the closer one.

Step-by-step bleed procedure – manual pump & hold method

  1. Attach clear plastic tubing to the bleed nipple on the caliper and place the other end in a clear bottle partially filled with clean brake fluid to prevent air re-entry.
  2. Have an assistant pump the brake lever or pedal several times and hold pressure. With pressure held, open the bleed nipple about a 1/4 turn to allow fluid and air to escape into the bottle. Close the nipple before the assistant releases pressure. Repeat until no air bubbles appear and fluid is clean. Keep the reservoir topped up between cycles to avoid drawing air into the master cylinder.
  3. Repeat this for each caliper in the specified order. Always close the bleed nipple firmly after each caliper is bled.
  4. For stubborn air, angle the ATV so trapped air migrates toward the reservoir — incline the machine slightly, never tilt violently. Pump and hold cycles help dislodge trapped air from caliper chambers.

Step-by-step bleed procedure – vacuum or pressure bleeder (preferred for one-person jobs)

  1. Connect vacuum pump to the bleed nipple or attach a pressure bleeder to the master cylinder reservoir per bleeder instructions.
  2. Open the bleed nipple and pull vacuum until fluid runs clear and bubble-free. Close nipple and move to the next caliper, keeping the reservoir topped with fresh fluid.
  3. If using a pressure bleeder, pressurize the reservoir as directed and open calipers sequentially until clean fluid flows.

Finishing checks

  • After bleeding, ensure each bleed nipple is tight and free of leaks. Wipe away any residual fluid.
  • Top reservoirs to proper level and reinstall diaphragms and caps securely.
  • Pump the brake lever/pedal several times until firm. If the lever feels spongy, re-bleed the system focusing on the caliper with recurring air.
  • Inspect hoses, banjo fittings, and caliper seals for leaks while cycling the brakes. Replace any worn or cracked hoses immediately.
  • Test brakes at low speed in a safe area before regular riding.

Maintenance tips specific to the BigBear 400

  • Pad inspection: the BigBear's calipers are straightforward to remove; inspect pads and replace if thickness is below manufacturer minimum or unevenly worn.
  • Banjo bolt torque: tighten banjo bolts and bleeder nipples snugly by feel; overtightening can strip threads in aluminum calipers. If you replace hardware, use new crush washers on banjo fittings.
  • Store brake fluid sealed and discard any opened bottles older than a few months; brake fluid absorbs moisture quickly.
  • If the front master cylinder lever is loose at the pivot or shows play after bleeding, inspect the pivot and lever assembly for wear and lubricate or replace parts as needed.

Performing a clean, methodical bleed will restore brake feel and reliability. If brakes still perform poorly after a complete bleed and inspection, contact a professional mechanic to check caliper pistons, master cylinder internal seals, or hidden leaks.

Related Shopping Categories

Shop Brake Fluid for a 2008 Yamaha BigBear 400 4X4 ATV.

Shop Brake Bleeders for a 2008 Yamaha BigBear 400 4X4 ATV.

Shop Brake Pads for a 2008 Yamaha BigBear 400 4X4 ATV.

Shop Brake Lines for a 2008 Yamaha BigBear 400 4X4 ATV.

Shop Brake Tools for a 2008 Yamaha BigBear 400 4X4 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.