How to Bleed and Replace Brake Fluid on a 1999 Yamaha Bigbear 350 2X4

Shop parts for a 1999 Yamaha Bigbear 350 2X4 ATV.

Overview

This guide from MotoSport walks you step-by-step through flushing and bleeding the brake fluid on a 1999 Yamaha Bigbear 350 2X4. Procedures below are written for a competent DIYer with basic tools. If you are unsure about any step, stop and get professional help.

Tools & Supplies

  • New DOT 3 or DOT 4 brake fluid (match the type already in system; do not use DOT 5 silicone)
  • Clear plastic tubing that fits snugly over bleeder nipples
  • Catch bottle or container
  • Wrench set (bleeder nipple size typically 8mm or 10mm)
  • Flat screwdriver or small pick (to remove rubber bleeder cap)
  • Clean rags and isopropyl alcohol for cleaning
  • Brake cleaner and a small brush (optional)
  • Safety glasses and nitrile gloves
  • Assistant (recommended for manual pump/hold method)
  • Torque wrench (for reassembly torque checks)

Safety Precautions

  • Brake fluid damages paintcover painted surfaces and wipe spills immediately with water and rags.
  • Work on a level surface with wheel chocked and engine off.
  • Dispose of old fluid per local regulations.

Model Notes for the 1999 Yamaha Bigbear 350 2X4

  • The Bigbear 350 2X4 is a simple, rugged ATV with conventional hydraulic brakes. Reservoirs may be separate for front/rear or combined depending on factory routingverify reservoir locations before starting.
  • On older Bigbears rubber hoses, seals and bleeder nipples can be corroded or swollen. Inspect lines and fittings; replace any hoses or hardware that show cracking, soft bulging or corrosion.
  • Caliper pistons on this model can seize or drag if fluid is old or contaminated. If one wheel is slow to bleed or pistons do not move freely when you compress the caliper, consider rebuilding the caliper or replacing it.
  • Banjo bolts and crush washers should be replaced if you disturb the hose-to-caliper connections.

Preparation

  1. Park ATV on level ground, apply parking brake (if fitted), and secure with wheel chocks.
  2. Locate the brake fluid reservoir(s). Clean the cap and surrounding area to prevent contamination.
  3. Remove the cap and top up the reservoir to the full mark with fresh DOT 3 or DOT 4 fluid. Keep the cap loosely in place to limit contamination while working.
  4. Raise the wheel(s) you will bleed and support the ATV so wheels turn freely. Use jack stands or blocksdo not rely on a jack alone.

Bleeding Procedure – General Single-Circuit Guidance

Follow the order: farthest wheel from master cylinder first, then next farthest, finishing with the wheel closest to the master cylinder. If you are unsure which is farthest, bleed rear then front. Use either the two-person pump-and-hold method or a one-person vacuum/pressure method.

Pump-and-Hold Method (Assistant required)

  1. Attach clear tubing to the bleeder nipple and route the other end into a catch bottle partially filled with fresh fluid to avoid air draw-back.
  2. Have your assistant pump the brake lever/pedal several times and hold firm pressure.
  3. Open the bleeder nipple about a 1/4 turn to let fluid and air escape. Close the nipple before the assistant releases the lever/pedal.
  4. Repeat: pump, hold, open, close, until fluid exiting the tubing is clean and free of bubbles.
  5. Top up the reservoir frequently so it never runs low; running the system dry introduces air and means restart from the beginning.
  6. Tighten the bleeder nipple to spec (hand tight then a small fraction with wrench) and replace the rubber cap.
  7. Repeat for each wheel in the bleed sequence.

Vacuum or Pressure Bleeder Method (One-person)

  1. Connect vacuum pump or pressure bleeder per tool instructions. If using vacuum at the caliper, use tubing to a clean bottle and apply steady vacuum while opening each bleeder briefly until clear fluid flows.
  2. If using a pressure bleeder on the reservoir, pressurize to the recommended psi, open bleeders in sequence until clear fluid without bubbles is observed, then close each bleeder before moving to the next.
  3. Maintain reservoir level during the entire procedure.

Special Tips for the Bigbear 350

  • If a caliper refuses to feed fresh fluid, remove it to inspect pistons and seals. Corrosion inside calipers is common on older ATVs.
  • If you find a stuck piston, a careful, gradual application of compressed air into the caliper fluid inlet while it is off the bike can push the piston out for rebuild — be cautious and use a rag to catch ejected fluid and protect the piston surface.
  • Replace crush washers on banjo bolts when disturbed; torque bolts to the correct spec to avoid leaks.
  • If the rear brake is drum-style (some variants), bleeding sequence is still applicable to any hydraulic slave cylinder; drum components require separate inspection for wear and proper adjustment.

Finishing Steps

  1. After bleeding all circuits, ensure reservoir is at the proper level and re-install cap securely.
  2. Clean any spilled fluid off painted surfaces immediately with water and then wipe with a clean rag.
  3. Lower the ATV, test lever/pedal feel. Brakes should be firm with minimal travel. If soft or spongy, repeat bleeding steps.
  4. Take the ATV for a low-speed test ride in a safe area to confirm braking performance. Avoid heavy braking until you are confident of proper function.
  5. Record date and mileage of fluid change; brake fluid typically should be replaced every 1-2 years depending on use and environment.

Common Problems & Solutions

  • Persistent air in system: Ensure reservoir never runs dry and use consistent bleed technique. Check for leaking connections or a cracked reservoir cap diaphragm.
  • Leaky bleeder nipples: Replace nipple and crush washer; ensure threads and mating surfaces are clean.
  • Brake drag after service: Check caliper piston retraction and pad clearance; caliper slide pins need cleaning and lubrication.

Parts & Consumables to Consider Replacing

  • Brake hoses (if rubber is aged or cracking)
  • Bleeder nipples and rubber caps
  • Caliper rebuild kits (seals, pistons where necessary)
  • Fresh DOT 3 or DOT 4 fluid
  • Banjo bolts and crush washers

Conclusion

Bleeding and replacing brake fluid on a 1999 Yamaha Bigbear 350 2X4 is straightforward when done methodically: keep the reservoir topped, follow the correct bleed order, and inspect hydraulic components for wear. For older Bigbears always inspect hoses, calipers and fittings for age-related deterioration and replace parts as needed to ensure safe, reliable braking.

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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.