How to Bleed & Replace Brake Fluid on a 1998 Honda TRX300 FOURTRAX 2X4

Shop parts for a 1998 Honda TRX300 FOURTRAX 2X4 ATV.

This MotoSport guide covers safe, professional steps to drain, replace, and bleed the hydraulic brake system on a 1998 Honda TRX300 FOURTRAX 2X4. Procedures below are written for the stock hydraulic front brake and the rear brake master cylinder system used on this model year. Use this as a shop-level how-to unique to MotoSport maintenance content.

What you’ll need

  • Fresh DOT 3 (or DOT 4 compatible) brake fluid – Honda recommends DOT 3; never mix with silicone-based fluids
  • Clear tubing that fits the bleeder nipple
  • Catch bottle or jar
  • Rubber gloves & eye protection
  • Bleeder wrench or appropriate open-end wrench for bleeder nipple
  • Syringe, turkey baster, or small suction pump to remove old fluid from the reservoir
  • Clean shop rags and brake-clean spray
  • Jack or stands to safely support the ATV if wheel removal is needed
  • Assistant for manual-pump bleeding (optional if using vacuum or pressure bleeder)

Model notes & cautions specific to the 1998 TRX300 FOURTRAX 2X4

  • This model is non-ABS; bleeding is manual/hydraulic only.
  • The front uses a hydraulic disc caliper system. The rear operates from a separate master cylinder/hydraulic circuit. Treat each circuit separately.
  • Reservoir & rubber components are old on a 1998 machine – inspect the reservoir cap diaphragm, lines, and banjo seals for cracking or swelling. Replace any aged rubber before relying on the system.
  • Use DOT 3 brake fluid unless you have already upgraded components and confirmed DOT 4 compatibility; always match the fluid type used previously or fully flush the system when changing types.
  • Brake fluid will damage paint & plastics. Protect surfaces — immediately wipe any spills and use brake cleaner on metal parts.

Preparation

  1. Park the ATV on level ground and secure it so it cannot roll. Remove key and disconnect battery if doing extended work.
  2. Clean the reservoir cap area thoroughly to prevent contamination when opening. For the TRX300, the front reservoir is on/near the handlebars & the rear master cylinder is by the right foot/near the frame — confirm which circuit you are servicing.
  3. Inspect lines, fittings, calipers, and the reservoir for corrosion, cracks, or leaks. Replace any damaged parts first.
  4. Raise the front or rear wheel if needed to access bleed nipples; support ATV securely on stands.

Drain & replace fluid (reservoir flush)

  1. Remove reservoir cap and diaphragm. Using a syringe or turkey baster, remove as much old fluid as possible from the reservoir. Dispose of used fluid properly.
  2. Refill the reservoir with fresh fluid to near the max line. Keep the cap off but do not let the fluid level run low during bleeding.
  3. If the old fluid is heavily contaminated or dark, perform multiple reservoir flushes: remove old fluid, refill, then bleed until expelled fluid is clear and bright.

Bleeding procedure – manual pump method

Bleed each circuit separately. Start with the line furthest from the master cylinder (commonly front caliper, then rear master cylinder circuit). Maintain reservoir fluid level throughout.

  1. Attach clear tubing to the bleeder nipple and route the other end into a catch bottle partially filled with a little fluid to prevent air re-entry.
  2. Have an assistant slowly apply the brake lever/pedal to build firm pressure, then hold it.
  3. With pressure applied, open the bleeder nipple about 1/4 turn to allow fluid and air to escape into the tubing. Close the nipple before the assistant releases the lever/pedal.
  4. Repeat pump-open-close cycles until the expelled fluid is clear and bubble-free. Keep the reservoir topped up between cycles to avoid sucking air into the master cylinder.
  5. When complete, tighten the bleeder snugly and wipe the area clean. Move to the next bleed point if the caliper has multiple bleeders; bleed the highest/outer caliper bleed first, then inward/next.

If using a vacuum or pressure bleeder

  • A vacuum pump at the bleeder nipple speeds the process: attach tubing, apply vacuum, open nipple, watch fluid flow until clean, then close nipple before removing vacuum. Ensure vacuum does not collapse hoses.
  • A pressure bleeder on the reservoir feeds clean fluid through the system — follow the tool manufacturer instructions and maintain correct pressure limits for ATV hydraulic systems.

Final steps & inspection

  1. Once all circuits show clear, bubble-free fluid and firm actuator feel, top reservoir to max line and reinstall diaphragm & cap securely.
  2. Pump the brake lever/pedal several times until firm resistance is felt and confirm no sink or sponginess. If spongy, re-bleed.
  3. Check all fittings, hoses, and the bleeder nipple for leaks while applying pressure.
  4. Inspect pads, rotors, drums, and hardware — replace worn pads or drums. Ensure caliper slide pins move freely after cleaning and lubrication with high-temp brake grease where applicable.
  5. Dispose of old brake fluid per local regulations; do not reuse.

Tips & common issues

  • Spongy brakes after bleeding usually indicate air remains in the system, the reservoir level dropped during bleeding, or there is moisture contamination in fluid — repeat the bleed and consider a full system flush.
  • If brake lever feels soft only when hot, old fluid moisture may be boiling — replace fluid and inspect for moisture ingress.
  • Inspect and replace aging rubber hoses; internal deterioration can introduce air and reduce brake performance.
  • After any brake service, perform a slow-speed test ride in a safe area to confirm proper operation before full use.

MotoSport maintenance reminder

MotoSport recommends using new OEM-quality seals, banjo washers, and fresh fluid when servicing older ATVs. For the 1998 TRX300 FOURTRAX 2X4, replacing the reservoir diaphragm, bleeder dust caps, and any suspect hoses during a brake fluid overhaul prevents repeated services and ensures reliable stopping power.

Related Shopping Categories

Shop Brake Fluid for a 1998 Honda TRX300 FOURTRAX 2X4 ATV.

Shop Brake Bleeders for a 1998 Honda TRX300 FOURTRAX 2X4 ATV.

Shop Brake Pads for a 1998 Honda TRX300 FOURTRAX 2X4 ATV.

Shop Brake Lines for a 1998 Honda TRX300 FOURTRAX 2X4 ATV.

Shop Brake Tools for a 1998 Honda TRX300 FOURTRAX 2X4 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.