How to Bleed & Replace Brake Fluid on a 2009 Yamaha BigBear 400 4x4
Shop parts for a 2009 Yamaha BigBear 400 4x4 ATV.
This MotoSport proprietary guide covers bleeding and replacing the hydraulic brake fluid on the 2009 Yamaha BigBear 400 4x4 (MMY). Follow these steps carefully to maintain braking performance and safety. If you’re unsure at any step, contact a qualified mechanic or MotoSport tech support for guidance.
Important model notes for the 2009 Yamaha BigBear 400 4x4 (MMY)
- The BigBear 400 uses a conventional, non-ABS hydraulic brake system with a front master cylinder/reservoir and a rear brake circuit. Identify the master cylinder reservoir location before starting.
- Factory brake fluid spec: use DOT 4 (or the manufacturer-recommended DOT rating stamped on the reservoir cap); don’t mix DOT 5 (silicone) with glycol-based DOT 3/4 fluids.
- Brakes are exposed to water, mud & vibration on this ATV. Seal condition around the caliper bleeder nipples and flexible hoses should be inspected while bleedingreplace any cracked or leaking hoses.
- Parking on a level surface and securing the ATV (chock wheels, put in park/neutral as appropriate) is critical for safe bleeding.
Tools & supplies
- DOT 4 brake fluid only (new, sealed container)
- Clear plastic tubing to fit bleed nipples
- Catch bottle (semi-transparent) or bleeder kit
- Wrenches for bleeder nipples (open-end or flare nut compatible)
- Assistant or a pressure/vacuum bleeder
- Clean rags, gloves, safety glasses
- Brake cleaner, small wire brush (for cleaning nipple area)
- Torque wrench for caliper/hose fittings if replacing parts
Preparation
- Park on a level surface, engage parking brake (if equipped) and chock wheels.
- Remove wheels or lift ATV for wheel access if necessary to reach calipers/bleeders comfortably.
- Clean around the master cylinder cap and each bleeder screw to prevent contamination.
- Inspect lines, hoses, and calipers for leaks, cracks or damaged fittings. Replace any suspect parts before bleeding.
Brake fluid replacement & bleeding procedure
- Remove the master cylinder reservoir cap and diaphragm. Siphon or absorb old fluid from the reservoir until it’s low but not empty. Keep the reservoir clean and covered to minimize contamination and moisture absorption.
- Top the reservoir with fresh DOT 4 fluid. Do not reuse fluid removed from the system.
- Identify the bleeding order: start with the caliper farthest from the master cylinder and work toward the closest. For most BigBear setups this typically means: rear caliper first (or the rear wheel furthest from the master), then front calipers, finishing with the caliper closest to the master cylinder. If uncertain, select the caliper that is visually farthest from the master cylinder as the starting point.
- Fit clear tubing over the bleeder nipple and submerge the other end in a small amount of fresh fluid in a catch bottle to prevent air re-entry.
- Have an assistant slowly depress and hold the brake pedal or lever. Open the bleeder nipple about a quarter- to half-turn. Fluid and air bubbles will flow into the tubing. Close the nipple before the assistant releases the pedal to prevent air from returning to the system. Repeat pump/open/close cycles until the expelled fluid runs clear with no air bubbles.
- Keep the master cylinder reservoir topped with fresh fluid during the entire process to avoid drawing air into the system. Never let the reservoir run dry.
- Move to the next caliper in the defined order and repeat until all circuits have clear, bubble-free fluid dispensed and the reservoir level remains steady.
- When finished, tighten all bleeder nipples snugly (don’t over-torque), wipe down components, and refill the reservoir to the correct level. Reinstall the cap and diaphragm securely.
- Operate the brake lever/pedal several times to confirm a firm, consistent feel. If the lever feels spongy, repeat bleeding. A pressure or vacuum bleeder can speed the task and often yields better results for stubborn air.
Finishing checks
- Inspect for leaks around bleeder screws, caliper banjo bolts and hoses. Torque fasteners to spec if replacing parts.
- Clean any spilled brake fluid immediately; it can damage plastics and painted surfaces.
- Properly dispose of used brake fluid per local regulations; do not reuse or pour on the ground.
- Test brakes at low speed in a safe area before returning to normal riding to ensure proper stopping performance.
Maintenance tips specific to the BigBear 400
- Brake fluid absorbs moisture over time; a routine flush every 1-2 years is a good preventive practice for off-road use and to avoid internal corrosion and boiling under heavy use.
- Because this ATV sees wet, muddy conditions, inspect and clean bleeder caps and caliper boots regularly to keep contaminants out of the system.
- If you notice persistent soft pedal/lever or frequent need to top up fluid, check for external leaks and caliper piston seals; worn seals can draw water/dirt into the system and require caliper service or replacement.
- Use OEM-quality replacement hoses and fittings where possible to maintain correct pressure and fitment for the MMY BigBear 400.
Follow this MotoSport guide to keep your BigBear 400 braking system reliable. If you need model-specific parts or replacement components, visit the MotoSport parts page linked above to find what fits your 2009 Yamaha BigBear 400 4x4.
Related Shopping Categories
Shop Brake Fluid for a 2009 Yamaha BigBear 400 4x4 ATV.
Shop Brake Bleeders for a 2009 Yamaha BigBear 400 4x4 ATV.
Shop Brake Pads for a 2009 Yamaha BigBear 400 4x4 ATV.
Shop Brake Lines for a 2009 Yamaha BigBear 400 4x4 ATV.
Shop Brake Tools for a 2009 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.