How to Bleed and Replace Brake Fluid on a 1991 Honda TRX300 FOURTRAX 2X4
Shop parts for a 1991 Honda TRX300FOUR ATV.
This MotoSport exclusive service guide walks you through safely replacing and bleeding the brake fluid on a 1991 Honda TRX300 FourTrax 2X4. Follow every step carefully & use clean tools and fresh fluid to protect braking performance and hydraulic components.
What you’ll need
- DOT 3 or DOT 4 brake fluid (do not mix with silicone-based fluids)
- Clear plastic hose and a catch bottle
- Wrench for bleed nipples (typically 8 mm) & basic socket set
- Turkey baster or syringe for removing old fluid from reservoir
- Clean rags, brake cleaner, gloves & eye protection
- Optional: pressure or vacuum bleeder, assistant for pedal/lever pumping
Safety first
- Work on a flat surface with the engine off and the parking brake engaged.
- Wear eye protection & gloves. Brake fluid is corrosive to paint & plastics.
- Keep the reservoir cap sealed as much as possible to avoid contamination.
Model notes specific to the 1991 TRX300 FourTrax 2X4
- The TRX300 commonly has front disc brakes and a rear drum; bleeding points differ by wheel type — caliper nipples for discs, wheel-cylinder bleed screws for drums.
- Original rubber lines & seals on a 1991 bike can be brittle. Inspect hoses, banjo fittings, and the master cylinder for cracks or leaks before and after bleeding.
- Master cylinder reservoir is relatively small — refill frequently during the process to prevent air entry.
- If brake hardware or wheel cylinders show heavy corrosion or leaks, replace parts before bleeding to avoid repeating the procedure.
Step-by-step: Replace and bleed brake fluid
- Clean the reservoir cap area. Remove the cap, diaphragm, and any old damp / dark fluid from the top using a syringe or turkey baster. Do not let debris fall into the reservoir.
- Fill the reservoir with new DOT 3 or DOT 4 brake fluid up to the full mark. Replace the cap loosely so the system isn’t exposed to dirt.
- Locate bleed nipples: front calipers and rear drum wheel cylinder. Put a clear hose on the nipple and route it into a catch bottle partially filled with fresh fluid to prevent air re-entry.
- Start with the wheel farthest from the master cylinder (typically the rear on many ATVs, then right front, then left front — if unsure, follow farthest-to-closest rule). For drum rear, you may need to access the brake plate to reach the wheel cylinder bleed screw.
- Have an assistant slowly pump the brake lever or pedal several times, then hold firm pressure. Open the bleed nipple about one-quarter to one-half turn to let fluid & air escape. Close the nipple before the assistant releases the lever/pedal. Repeat until only clear fluid free of bubbles flows into the hose.
- Keep the master reservoir topped off during the entire process. Never let it run dry or you will reintroduce air into the system.
- Repeat bleeding at each wheel in the chosen sequence. For drum brakes, operate the brake pedal/lever exactly as above while a bleeder is opened & closed; you may need to actuate the pedal more strokes to clear the wheel cylinder.
- After all points are bled, torque bleed nipples to spec snugness (do not over-torque). Wipe all fittings clean.
- Top the reservoir to the correct level, reinstall cap and diaphragm, and clean any spilled fluid from painted surfaces with water and mild detergent followed by drying.
- Test lever/pedal feel with the engine off: controls should be firm. If spongy, re-bleed the system, focusing on the most distant circuit first.
- Lower the ATV and perform a careful slow-speed brake test in a safe area. Check for leaks, drag, or uneven braking. Re-check reservoir level after a short test ride and again after several stops.
Tips & troubleshooting
- If you see persistent bubbles, inspect the master cylinder cap diaphragm and reservoir for cracks or the hose routing for air leaks.
- Soft or sinking lever/pedal after bleeding indicates either remaining air or internal leaks in the master cylinder or wheel cylinders; rebuild or replace the leaking component.
- Replace rubber hoses if they show swelling when pressure is applied or visible cracks. Old rubber is a common cause of brake failure on vintage machines.
- Dispose of used brake fluid responsibly at a hazardous-waste facility; do not pour down drains.
Final inspection
- Ensure bleed nipples and banjo bolts are tight and leak-free. Inspect shoes, pads, rotors and drums for wear and contamination from fluid.
- Confirm brake performance under light, controlled conditions before normal use.
Perform this service every 1-2 years or sooner if fluid darkens or braking feels compromised. Regular fluid changes will extend the life of the hydraulic components and keep your 1991 TRX300 FourTrax 2X4 stopping reliably.
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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.