How to Bleed & Replace Brake Fluid on a 1989 Yamaha Bigbear 350 4X4

Shop parts for a 1989 Yamaha Bigbear 350 4X4 ATV.

This MotoSport-exclusive guide walks you through safely draining, replacing, and bleeding the brake fluid on a 1989 Yamaha Bigbear 350 4X4 (MMY). Procedures below are written for the stock hydraulic components on this model; follow each step carefully and use MotoSport-quality replacement parts and fluids when reassembling.

Before you start

  • Park on level ground, set parking brake, remove ignition key, disconnect battery negative terminal if working near electrical parts.
  • Recommended fluid & compatibility: use DOT 3 brake fluid unless your OEM placard specifies DOT 4. Do not mix DOT fluids with mineral oil systems.
  • Protect finish: brake fluid damages paint & plastics – cover fenders and frame areas under the reservoir.
  • Have these tools ready: proper-size wrenches, clear plastic tubing, catch bottle, new DOT 3 (or OEM spec) fluid, turkey baster or fluid syringe, clean rags, rubber gloves, torque wrench, jack/stands if needed, and a helper for manual bleeding.

Model-specific notes for the 1989 Bigbear 350 4X4

  • The Bigbear uses a simple hydraulic front disc/rear drum-style layout on many of these model years; confirm whether your rear is drum or disc — bleed points will differ. The front caliper bleeder is on the caliper; the rear wheel cylinder or caliper has the bleeder screw.
  • Reservoir location: master cylinder reservoir is behind the handlebars under a rubber cap – clean around the cap before opening to keep contaminants out.
  • Brake line routing on the Bigbear is exposed along the swingarm and front forks — inspect lines for cracking, chafing, or rusted fittings and replace if aged before bleeding.
  • If your Bigbear has ABS retrofit or aftermarket parts, follow those component instructions; this guide covers standard non-ABS hydraulic systems.

Overview of the procedure

1) Remove old fluid from the master cylinder reservoir. 2) Flush system by adding fresh fluid and pumping to push old fluid toward bleed screws. 3) Open bleeder at each wheel in the correct sequence, drawing fluid until clear and bubble-free. 4) Top reservoir frequently to avoid introducing air. 5) Torque bleed screws to spec, clean up, bench test, then road test carefully.

Step-by-step: preparing and draining the reservoir

  1. Clean the area around the reservoir cap. Remove cap and diaphragm carefully.
  2. Use a turkey baster or fluid syringe to remove as much old fluid as possible from the reservoir.
  3. Refill reservoir with fresh DOT 3 (or OEM-specified) fluid to the MAX line. Replace diaphragm and loosely reseat cap so you can monitor fluid level during bleeding.

Step-by-step: manual bench-bleed or pressure prep

  • If you have a bench-bleeder or pressure bleeder from MotoSport, use it per tool instructions; it makes the job faster and helps avoid air ingestion.
  • If bench tools aren't available, proceed with helper-assisted manual bleeding: park the ATV so bleed nipples are accessible; keep the reservoir topped during the process.

Bleeding order and technique

Bleed in this sequence for best results: farthest wheel from master cylinder first, then work toward the master. On the Bigbear that typically means:

  1. Rear wheel (if rear is a hydraulic component and is the farthest),
  2. Front passenger-side wheel (if applicable),
  3. Front driver-side wheel (closest to master).

Procedure for each bleeder:

  1. Attach clear tubing to the bleeder nipple – other end into a catch bottle partially filled with old fluid to prevent air from re-entering.
  2. Have your helper slowly depress the brake lever/pedal several times and hold it to the floor.
  3. Open the bleeder one-quarter to one-half turn with a wrench until fluid and air bubbles flow into the tubing; close the bleeder before the helper releases pressure.
  4. Repeat pump-hold-open-close cycles until the fluid runs clear with no bubbles. Keep reservoir topped between cycles.
  5. Tighten bleeder to a snug torque (hand tight plus a quarter turn; avoid over-torquing) and wipe away spilled fluid immediately.

Flushing a stubborn system

  • If fluid remains dark or contaminated, perform multiple reservoir refills and repeated bleeding cycles until new fluid exits clear.
  • For hard-to-remove air pockets, elevate wheels or use gravity bleeding by raising the bleeder above the master to help air escape.

After bleeding

  • Top reservoir to MAX, reinstall diaphragm and cap, and clean any spilled fluid from paint or metal surfaces.
  • Reconnect battery negative terminal if it was disconnected.
  • Check pedal/leverage feel at rest — it should be firm with no sponginess. If spongy, repeat bleeding.
  • Road test at low speed in a safe area, applying brakes progressively to confirm consistent, firm braking. Recheck fluid level and bleeder screws after test.

Safety & maintenance tips

  • Always dispose of old brake fluid responsibly per local regulations.
  • Replace rubber hoses older than 6-8 years or with visible wear; rubber degrades and traps air.
  • Inspect master cylinder cap diaphragm for hardening or cracks — replace if compromised to prevent moisture ingress.
  • Bleed the system at least every 2 years or sooner if the brake feel degrades, fluid darkens, or the system has been opened.

Troubleshooting

  • Persistent spongy lever after thorough bleeding: suspect internal master cylinder seal leakage or collapsed hose. Inspect and replace faulty components before re-bleeding.
  • Leaking bleeder or caliper: replace or rebuild the caliper/wheel cylinder and re-bleed.

Follow these steps to keep your 1989 Yamaha Bigbear 350 4X4 stopping reliably. For model-specific replacement parts, brake hoses, caliper rebuild kits, and recommended fluids, rely on MotoSport-sourced components to maintain OEM-level safety and fitment.

Related Shopping Categories

Shop Brake Fluid for a 1989 Yamaha Bigbear 350 4X4 ATV.

Shop Brake Bleeders for a 1989 Yamaha Bigbear 350 4X4 ATV.

Shop Brake Pads for a 1989 Yamaha Bigbear 350 4X4 ATV.

Shop Brake Lines for a 1989 Yamaha Bigbear 350 4X4 ATV.

Shop Brake Tools for a 1989 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.