How to Bleed and Replace Brake Fluid on a 2012 Yamaha BigBear 400 4X4

Shop parts for a 2012 Yamaha BigBear 400 4X4 ATV.

This MotoSport guide walks you through a safe, efficient brake fluid replacement and bleeding procedure specific to the 2012 Yamaha BigBear 400 4X4. Follow each step carefully, use the correct fluid for your machine, and observe all safety precautions. This procedure is written for owners who have basic mechanical experience and the proper tools.

What you need

  • Yamaha-approved brake fluid (check your owner’s manual for DOT specification — DOT3 or DOT4 as specified)
  • Wrench set and combination pliers
  • Brake-bleeder wrench or correct-size box wrench for bleeder screws
  • Clear plastic tubing and a catch bottle
  • Turkey baster or fluid siphon
  • Clean lint-free rags and disposable gloves
  • Brake cleaner and a small brush
  • Jack or stands to safely support the vehicle if needed
  • Optional: vacuum bleeder or pressure bleeder for faster, one-person bleeding

Safety and prep

  • Work on a level surface with the engine off and key removed.
  • Protect painted and plastic surfaces from contact with brake fluid; it will damage finishes.
  • Keep the reservoir cap and fluid bottle closed except when adding fluid — brake fluid is hygroscopic (absorbs water) and must be kept fresh.
  • Wear gloves and eye protection. Dispose of old fluid responsibly.

Model-specific notes for the 2012 Yamaha BigBear 400 4X4

  • The BigBear 400 uses hydraulic brakes with a master cylinder reservoir mounted on the handlebar (front) and a rear master cylinder/reservoir located near the rear brake pedal depending on your model configuration. Confirm which circuits are present on your machine before starting.
  • There is no electronic ABS system to complicate bleeding on this model, but dual-circuit systems require bleeding both circuits until clear fluid appears.
  • Inspect calipers, lines and banjo fittings for leaks, wear or corrosion while you work. The BigBear is commonly ridden in wet & muddy conditions, so pay special attention to line chafe, banjo bolt seals, and caliper boots.
  • If you notice spongy brakes after bleeding, inspect master cylinder seals and caliper pistons for damage or sticking; the BigBear’s service life in rough terrain can accelerate component wear.

Preparation steps

  1. Park the ATV securely and remove any cargo. If you need wheel access, support the machine with jack stands and remove wheels per factory guidance.
  2. Clean the reservoir cap area to prevent contamination. Remove the cap and diaphragm, then siphon or carefully pour out old fluid until the reservoir is nearly empty.
  3. Top the reservoir with fresh fluid and keep the cap loosely in place to limit contamination while allowing pressure equalization during bleeding.
  4. Identify the calipers and bleeder screws. Place catch bottles beneath each bleeder and fit clear tubing over the screw to direct fluid into the bottle.

Bleeding sequence and methods

General principle: bleed the circuit starting with the caliper farthest from its master cylinder and finish with the nearest. Use one of the methods below.

Two-person manual pump method

  1. Person A pumps the brake lever or pedal slowly several times and holds it fully applied.
  2. Person B opens the bleeder screw a 1/4 to 1/2 turn. Fluid and air will flow into the tube. Close the bleeder screw before Person A releases the lever/pedal.
  3. Repeat until the expelled fluid is clear and free of bubbles, maintaining the reservoir level between minimum and maximum to avoid introducing air.
  4. Move to the next farthest caliper and repeat until all calipers in that circuit are clear.

One-person vacuum or pressure bleeder

  1. Attach vacuum pump to the bleeder fitting or use a pressure bleeder on the reservoir per tool instructions.
  2. Open the bleeder and draw fluid until it flows clear and bubble-free. Close the bleeder before releasing vacuum, or follow the pressure bleeder manufacturer’s procedure for safe depressurization.

Gravity bleed (slow) method

  1. Top the reservoir and open bleeders in sequence from farthest to nearest. Allow fluid to flow by gravity until clear fluid exits. This is slow but useful if you lack tools.
  2. Monitor and top the reservoir frequently.

Front and rear circuit tips

  • If the BigBear has separate front and rear reservoirs/circuits, complete the full bleed of one circuit before starting the other.
  • If there is a combined reservoir feeding multiple circuits, bleed the circuit designated as farthest first, then the other(s).
  • Always keep the reservoir filled to prevent air from being drawn back into the lines.

Finishing up

  1. With clear fluid and no air bubbles at each bleeder, close all bleeder screws to the specified snugness (hand-tight plus a short turn; avoid over-torquing banjo bolts and bleeders).
  2. Top each reservoir to the proper level, reinstall diaphragms and caps, and wipe any spilled fluid from painted surfaces with brake cleaner immediately.
  3. Reinstall wheels if removed and torque axle nuts/lug nuts to spec.
  4. Test brake lever/pedal feel at low speed in a safe area before returning to normal riding. Brakes should be firm and responsive; if spongy, repeat bleeding or inspect components for leaks or internal damage.

Maintenance tips and troubleshooting

  • Change brake fluid periodically per service schedule; if fluid is dark or contaminated, replace it. Fresh fluid extends seal life and improves braking performance.
  • If you cannot get firm brakes after repeat bleeding, inspect master cylinder bore, caliper pistons, and seals for wear or damage. Mud and water ingestion are common causes of component failure on BigBear machines used in wet terrain.
  • Replace copper crush washers on banjo fittings when disturbed to ensure leak-free seals.
  • Record the fluid type and date of service for future maintenance tracking.

Common pitfalls to avoid

  • Never mix different types of brake fluid in the system unless both are compatible per the vehicle manual.
  • Do not let the reservoir run dry during bleeding — that introduces air and requires restarting the process.
  • Avoid using petroleum-based cleaners on rubber seals; use brake cleaner or isopropyl where appropriate.

Follow these steps carefully and the braking system on your 2012 Yamaha BigBear 400 4X4 will be refreshed and reliable. If you encounter a persistent problem or internal master cylinder/caliper damage, consult a qualified technician or MotoSport service resources.

Related Shopping Categories

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Shop Brake Lines for a 2012 Yamaha BigBear 400 4X4 ATV.

Shop Brake Tools for a 2012 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.