How to Bleed & Replace Brake Fluid on a 1987 Yamaha Bigbear 350 4X4

Shop parts for a 1987 Yamaha Bigbear 350 4X4 ATV.

This MotoSport-exclusive guide walks you through a safe, complete brake-fluid change and bleed procedure specific to the 1987 Yamaha Bigbear 350 4X4 (MMY). Follow each step carefully, use proper tools, and replace worn hardware you discover along the way.

What you need

  • Clean DOT 3 or DOT 4 brake fluid (check current master-cylinder cap marking; DOT 3 is commonly used)
  • Brake-bleeder wrench or box wrench set
  • Clear vinyl tubing & a catch bottle (marked for used brake fluid)
  • Vacuum or pressure bleeder (optional for one-person bleeding)
  • Clean rags, gloves, eye protection
  • Stiff wire brush, small screwdriver, pliers
  • Replacement bleed-screw crush washers or new bleeder screws if corroded
  • Service manual or torque wrench for fastener specs

Model notes – what owners of the 1987 Bigbear 350 should know

  • The 1987 Bigbear 350 uses hydraulic brakes with wheel cylinders/bleeder screws at the hubs. It is an older MMY design so expect surface corrosion on bleeders, fittings and lines if original.
  • Rubber lines can age and swell — inspect for cracking, soft spots or leaks. Replace if more than surface wear is present.
  • Brake shoes, wheel cylinders and backing plates should be inspected when removing wheels. Contamination from leaking wheel cylinders is common on older machines.
  • Brake fluid will attack paint and plastic — protect the finish and wipe spills immediately.
  • If the master-cylinder reservoir is metal, check for internal corrosion and debris; consider rebuilding or replacing if fluid looks rusty or contaminated.

Preparation

  • Park the ATV on level ground, secure with chocks and engage parking brake.
  • Remove the seat and any body panels necessary to access the master-cylinder reservoir and bleed nipples on the wheel cylinders.
  • Clean the reservoir cap area; prevent dirt from entering the system. Remove cap and diaphragm carefully and inspect fluid color.
  • Record initial fluid level and condition. Very dark or dirty fluid means a full flush is required, not just topping off.

Bleed order (recommended)

Bleed starting with the wheel farthest from the master cylinder and finish with the closest. On many Bigbear layouts that means: rear passenger-side > rear driver-side > front passenger-side > front driver-side. If in doubt, identify master-cylinder location and work outward.

Step-by-step – full fluid replacement and bleed

  1. Top off reservoir with fresh brake fluid so it never runs dry during the procedure.
  2. Attach clear tubing to the bleeder screw on the farthest wheel. Submerge the other end in a small container partially filled with fresh fluid to prevent air re-entry.
  3. Have a helper slowly depress the brake pedal several times and hold it down. With pedal depressed, open the bleeder screw about 1/4 turn until fluid runs into the tubing. Close the screw, then allow the pedal to return. Repeat until fluid runs clear and free of bubbles. Keep reservoir topped between cycles.
  4. Repeat the process for each wheel in the bleed order. If you're using a vacuum or pressure bleeder, follow the tool instructions but maintain the same sequence.
  5. After all wheels are bled, cycle the pedal to ensure it feels firm. If it's spongy, repeat bleeding or inspect for leaks/air entry points.
  6. Wipe all fittings clean, torque bleeder screws to the specified value if available, and replace crush washers where applicable.
  7. Fill the reservoir to the correct level, reinstall diaphragm & cap, and clean any spilled fluid from painted surfaces. Test brakes at low speed before returning to normal use.

One-person vacuum/pressure bleed method

  • Use a vacuum pump on each bleeder or a pressure bleeder on the reservoir. This reduces pedal cycling and helps pull contaminants out of the system.
  • Observe fluid color & air bubbles; rotate through wheels until fluid remains clean.

Inspection & replacement tips

  • If bleeder screws are corroded, replace them. Damaged screws can round off and make future service difficult.
  • Replace rubber lines that show cracking or soft spots. New lines prevent internal collapse during braking and provide consistent pressure.
  • Inspect wheel cylinders/shoes for leaks and contamination. Rebuild or replace cylinders if they bleed fluid onto the shoes.
  • Consider a master-cylinder rebuild kit if the pedal requires extra travel after bleeding or if the reservoir cap shows corrosion.
  • Always dispose of used brake fluid responsibly; it is contaminant-laden and should not be poured down drains.

Common issues & troubleshooting

  • Spongy pedal after bleeding: likely remaining air, a leak, or a collapsed hose. Recheck fittings and hose condition.
  • Brake drag after bleeding: overly-tightened cables, seized wheel cylinders, or misadjusted shoes. Inspect components and adjust or rebuild as needed.
  • Persistent contamination: perform a system flush by repeatedly drawing fresh fluid through until it runs clear at every bleeder.

Final checks

  • Confirm no leaks and that wheel nuts, caliper/wheel-cylinder bolts, and bleeder screws are secure.
  • Test-ride at low speed in a safe area to verify braking performance, then recheck fluid level after the first use.
  • Log the service date and fluid type used for future maintenance intervals.

For any questions about parts or model-specific components for your 1987 Yamaha Bigbear 350 4X4 contact MotoSport’s parts specialists through the product page linked above.

Related Shopping Categories

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Shop Brake Lines for a 1987 Yamaha Bigbear 350 4X4 ATV.

Shop Brake Tools for a 1987 Yamaha Bigbear 350 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.