How to bleed and replace brake fluid on a 2000 Yamaha BigBear 400 2x4
Shop parts for a 2000 Yamaha BigBear 400 2x4 ATV.
The following MotoSport proprietary guide walks you through a complete brake fluid replacement and bleeding procedure for a 2000 Yamaha BigBear 400 2x4. It covers preparation, safety, system-specific notes for the BigBear MMY, step-by-step fluid replacement and bleeding for both disc and drum components, troubleshooting, and recommended maintenance intervals.
What you need
- Correct brake fluid as specified by Yamaha (consult owner’s manual; DOT 3 or DOT 4 are common) use fresh, unopened fluid
- Clear plastic tubing to fit bleed nipples
- Catch bottle (glass or plastic) with some brake fluid in the bottom to prevent air draw-back
- Wrenches for bleed nipples (usually 8mm to 10mm)
- Syringe or turkey-baster (for reservoir fluid removal)
- Brake cleaner and rags
- Jack or stands to lift the ATV safely; wheel chocks
- Latex or nitrile gloves and eye protection
Model notes — 2000 Yamaha BigBear 400 2x4
- The BigBear 400 2x4 uses a hydraulic brake system driven by a master cylinder(s) and wheel cylinders or calipers. Trim and regional variants may have front and/or rear drum or disc components. Confirm which configuration your unit has before starting.
- Brake components on this model are exposed to mud and water during typical use. Inspect boots, seals, lines and bleed nipples for corrosion or pinholes before beginning. Replace any compromised parts rather than attempting to bleed a leaking system.
- Reservoir lids may have a diaphragm; keep the area clean and avoid introducing dirt into the system while opening.
- Use only the brake fluid type recommended by Yamaha for compatibility with seals and paint. Avoid mixing DOT types unless manufacturer allows it; if switching types, flush the system thoroughly.
Preparation
- Park the ATV on level ground, engage parking brake or block wheels, and disconnect battery negative terminal if you will be working under the front cowling to avoid shorts.
- Clean the brake reservoir cap area thoroughly to avoid contamination.
- Remove enough old fluid from the reservoir with a syringe so you can add fresh fluid without spilling when you pump or open the system.
- Inspect lines, hoses and fittings. If hardware or hoses are brittle, swollen or leaking, replace them first.
Brake fluid replacement strategy
Two common methods work well: the one-person pump-and-hold method with a helper opening the bleed nipple, or a vacuum/suction bleeder. Both are covered below. The goal is to replace all old fluid and remove trapped air.
Order to bleed (recommended)
- Bleed the wheel farthest from the master cylinder first, then move progressively closer. For the BigBear 400 2x4 this usually means rear (if separate) then front. If single combined circuit, follow the same principle: farthest wheel, then next, finish at the closest to the master cylinder.
Step-by-step — one-person method with clear tubing
- Fit clear tubing securely over the bleed nipple and place the other end into a catch bottle partially filled with fresh brake fluid. The tubing end in the bottle should be submerged in fluid to prevent air re-entry.
- Top up the master cylinder reservoir with fresh fluid until it’s at the fill line. Keep the cap loosely seated so pressure changes can vent but no dirt falls in.
- Have a helper slowly apply steady pressure to the brake lever or pedal (about half to two-thirds travel) and hold it. If working alone, use a padded clamp or lever-holder while monitoring fluid level carefully.
- While the lever/pedal is held, open the bleed nipple a 1/4 to 1/2 turn until fluid and bubbles flow into the tubing. Close nipple before the helper releases the lever. Repeat pump-hold-open-close cycles until clear, bubble-free fluid appears and volume drawn contains only new fluid.
- After each cycle, immediately top up the master reservoir. Never allow the reservoir to fall near empty or air will be drawn into the system.
- When that wheel is clear, tighten the bleed nipple to the specified torque (do not overtighten), wipe clean, and move to the next wheel following the bleed order.
- After bleeding all wheels, ensure the reservoir is filled to the proper level, secure the cap, and test lever/pedal firmness. If the lever is spongy, repeat bleeding until firm.
Step-by-step — vacuum bleeder (recommended for one person)
- Attach vacuum bleeder to the master cylinder reservoir per tool instructions.
- Fit clear tubing on the bleed nipple and place into catch bottle.
- Create a light vacuum at the reservoir and open the bleed nipple until continuous fluid, free of bubbles, flows into the bottle. Keep reservoir topped with fresh fluid to prevent air entry.
- Close bleed nipple, move to the next wheel, repeat until all circuits are clear.
- Release vacuum, top off reservoir, clean cap sealing surfaces and reassemble.
Bleeding drum wheel cylinders (if applicable)
- Drum wheel cylinders bleed the same way as calipers. Remove drum per service manual to gain access if needed. Soft or spongy pedal after bleeding drum components often indicates shoe contamination or warped drums; inspect and service as necessary.
Final checks and test
- Ensure all bleed nipples are tight and caps/reservoir covers are sealed. Clean any spilled fluid from painted surfaces immediately; brake fluid can damage paint and plastics.
- With the ATV still supported, operate the brakes several times to check for firm response. Lower the ATV and perform a low-speed road test in a safe open area to confirm braking performance.
- Recheck for leaks, and recheck fluid level after test ride; top as required.
Troubleshooting
- Persistent spongy pedal after thorough bleeding: inspect master cylinder seals, flex hoses (collapse internally), wheel cylinders/calipers for leaks, and ABS or proportioning valves if equipped. Replace suspect components rather than repeatedly bleeding air into a compromised system.
- If no fluid moves when opening a bleed nipple: check master cylinder internal condition, reservoir pathways for blockages, and fitment of the tubing on the nipple.
- Air that keeps returning often indicates a leak or a failing master cylinder seal drawing air in when the pedal is released.
Maintenance interval & storage notes
- Brake fluid attracts moisture over time. MotoSport recommends replacing brake fluid every 1-2 years for recreational ATVs, or sooner with heavy use in wet/dirty conditions.
- Store replacement fluid in a sealed container; brake fluid that has been open to air for long periods should be discarded.
- After off-road use in deep water, inspect brakes and consider bleeding if you notice water ingress or soft brake feel.
Parts & replacement recommendations
- Replace rubber hoses and bleed nipples if crusted with corrosion, cracked or soft. Use OEM-spec fittings and recommended torque values when reassembling.
- If master cylinder rebuilding is necessary, use a rebuild kit designed for the BigBear 400 master cylinder to ensure correct seal materials.
- Always tighten bleed nipples to proper spec, and replace nipple washers if applicable.
Following this MotoSport proprietary procedure will give you a clean, reliable brake system on your 2000 Yamaha BigBear 400 2x4. Regular inspection and using correct fluid will protect seals and maximize stopping performance.
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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.