How to Bleed and Replace Brake Fluid on a 1990 Honda TRX300 FOURTRAX 2X4

Shop parts for a 1990 Honda TRX300FOUR ATV.

This MotoSport guide gives a clear, safe procedure to flush and bleed the brake system on a 1990 Honda TRX300 FOURTRAX 2X4. Follow each step carefully, use the proper fluid, and address model-specific notes near the end.

What you'll need

  • DOT 3 brake fluid (Honda recommends DOT 3; DOT 4 is acceptable if specified on replacement parts)
  • Brake bleeder wrench or appropriate box wrench
  • Clear plastic tubing to fit bleed nipple
  • Catch bottle partially filled with old fluid to prevent air reintake
  • Turkey baster or fluid syringe (to remove reservoir fluid)
  • Clean rags and brake-safe parts cleaner
  • Gloves and eye protection
  • Jack and stands or ramps to raise wheels for access (if needed)
  • Assistant for manual push-bleeding (recommended)

Safety first

  • Work on a level surface with the engine off and parking brake applied. Remove spark plug wires to prevent accidental starts when working nearby.
  • Brake fluid damages paint and plastics — wipe spills immediately.
  • Dispose of contaminated fluid properly.

Prepare the ATV

  1. Clean the master cylinder reservoir cap and area around it to keep dirt out.
  2. Remove the cap and diaphragm. Siphon or turkey-baste as much old fluid out as possible to minimize contamination when refilling.
  3. Top the reservoir with fresh DOT 3 fluid to the recommended level. Keep cap off but reservoir covered loosely with a clean rag to minimize dust.
  4. Identify bleed nipples on the caliper(s) or wheel cylinder(s). On the TRX300 you may have front caliper(s) and a rear caliper or drum — locate accordingly.

Bleeding sequence and method

General rule: start at the wheel farthest from the master cylinder and finish at the closest. For the TRX300 common sequence is rear right, rear left (if dual), then front(s). If your machine has a single rear drum with a wheel cylinder, bleed the wheel cylinder last.

Manual two-person bleed (recommended)

  1. Have your assistant sit on the machine and apply steady firm pressure to the brake lever or pedal when instructed.
  2. Attach clear tubing to the bleed nipple; place other end into the catch bottle partially filled with old fluid to prevent drawing air back in.
  3. Open the bleed nipple about a quarter to half-turn. Instruct assistant to slowly squeeze brake lever/pedal until you see fluid and bubbles in the tubing. Close the nipple while pressure is applied, then instruct assistant to release lever/pedal. Repeat until fluid runs clear with no air bubbles.
  4. Top up the reservoir between cycles so it never runs low.
  5. Proceed through each wheel in the proper sequence.

One-person push-bleed (if no assistant)

  1. Use a one-way valve bleeder or a Mity-Vac type pump to pull fluid through. Alternatively, push the lever/pedal slowly and hold while you open and quickly close the bleed nipple, then reseat the nipple before releasing brake pressure.
  2. Maintain reservoir level throughout; repeat until clear fluid with no bubbles exits each bleed point.

Finishing steps

  1. When all circuits are clear, tighten bleed nipples to spec (hand tight plus quarter-turn, or per torque spec if known), then wipe clean.
  2. Top the reservoir to the MAX line, reinstall diaphragm and cap securely.
  3. Pump the brake lever/pedal several times with the engine off until you get a firm pedal feel. If the lever/pedal is spongy, recheck for air and repeat bleeding.
  4. Test brakes at low speed in a safe area before normal riding.
  5. Clean any spilled fluid and dispose of waste fluid responsibly.

Model-specific notes for the 1990 TRX300 FOURTRAX 2X4

  • The 1990 TRX300 is a simple hydraulic system with no ABS; bleeding follows conventional caliper/wheel-cylinder practice.
  • Older rubber hoses and seals can absorb moisture; if the fluid was very dark or contaminated, consider replacing flexible brake hoses and the master cylinder diaphragm when servicing.
  • Parking brake linkage and rear drum components (if equipped) can be rusty on older units — inspect and lubricate pivot points when working at the rear wheel.
  • Use new DOT 3 fluid after a full replacement; avoid mixing DOT 5 (silicone) with glycol-based fluids. DOT 4 is compatible if needed for higher boiling point, but DOT 3 is the factory standard for this era.
  • Bleed frequency: every 1-2 years for reliability and contamination prevention, or immediately if you detect soft pedal, contamination, or moisture intrusion.

Troubleshooting

  • Persistent spongy lever/pedal after bleeding: recheck for air leaks at hose fittings, master cylinder seals, or caliper pistons; inspect hoses for internal collapse.
  • Brake drag after bleeding: ensure caliper pistons fully retract and adjust parking brake as needed; debris or corroded sliders can cause sticking.
  • If you encounter seized bleed nipples, apply penetrating oil and avoid rounding the nut; use a correctly fitting wrench.

Following these steps keeps your TRX300 FOURTRAX braking performance safe and reliable. Replace worn hydraulic components when in doubt and keep fresh DOT 3 fluid on hand for regular maintenance.

Related Shopping Categories

Shop Brake Fluid for a 1990 Honda TRX300FOUR ATV.

Shop Brake Bleeders for a 1990 Honda TRX300FOUR ATV.

Shop Brake Pads for a 1990 Honda TRX300FOUR ATV.

Shop Brake Lines for a 1990 Honda TRX300FOUR ATV.

Shop Brake Tools for a 1990 Honda TRX300FOUR 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.