How to Bleed the Front Brakes on a 1993 TRX 300 FourTraxby Chris Gilliland
Honda's 1993 TRX300 FourTrax all-terrain vehicle was equipped with a hydraulic front brake system. Unlike standard hydraulic brakes, which are typically paired with disc-like brake rotors, the TRX300 relied on a drum-style brake assembly attached to both front wheels. Over time, the fluid within the brake system could develop air bubbles and absorb water in the form of condensation, reducing the brakes' efficiency. This is often felt as reduced braking capability and a soft, almost sponge-like feeling from the brake lever. Removing water and air-contaminated brake fluid is done through a set of valves built into the front brake.
Loosen the front wheel lug nuts on both sides of the ATV, using a 17 mm socket and a breaker bar. Lift the front wheels off of the ground using a jack placed beneath the ATV's engine. Unscrew the lug nuts and pull both wheels off of the front wheel hubs.
Remove the front brake master cylinder's rectangular fluid reservoir cover using a Phillips screwdriver. Pull the inner diaphragm out of the reservoir, then suck out the old brake fluid using a syringe or hand pump. Refill the reservoir with fresh DOT 3 brake fluid until the fluid is level with the top of the round reservoir sight gauge.
Tap the front brake master cylinder and the upper brake line fitting lightly to dislodge any trapped air bubbles, then pull and release the brake lever several times to draw fresh brake fluid into the brake circuit. Refill the reservoir if the fluid level drops significantly.
Remove the rubber dust cap from the left front brake bleed valve, located at the rear of the left front wheel hub. Push a three-foot length of clean 1/4-inch inner diameter plastic hose over the bleed valve, then lay the free end of the hose in a plastic catch container.
Have an assistant pull in and hold the front brake lever firmly in place. Turn the bleed valve counterclockwise a quarter-turn using an 8 mm crescent wrench. A small stream of brake fluid will shoot into the plastic hose as the valve is opened. Turn the valve counterclockwise to close it, then instruct your assistant to slowly release the brake lever. Repeat two to three times to fill the plastic hose with brake fluid.
Inspect the condition and color of the brake fluid trapped within the hose. When fresh, brake fluid is clear and has a light tan hue. If the brake fluid appears dirty or contains air bubbles, you must continue bleeding the brake circuit.
Open the bleed valve and have your assistant pull in and hold the brake lever in place. Close the bleed valve, then have your assistant slowly release the lever. Continue to bleed the left front brake in this manner until the fluid caught in the hose is free of air bubbles and clear.
Pull the hose off of the left front brake bleed valve using a shop towel. Wipe away any spilled fluid, then push the rubber dust cap onto the valve. Refill the master cylinder reservoir with DOT 3 brake fluid.
Remove the rubber dust cap from right front brake bleed valve, then push the plastic hose onto the valve. Bleed the right front brake, using the same method as the left brake. Stop when the brake fluid is clear and free of air bubbles.
Pump the front brake lever in several times. The lever should feel firm a quarter to half of the way into its stroke, indicating that there is hydraulic pressure in the brake circuit. If the lever feels soft and provides a sponge-like sensation, re-bleed the front brakes, starting with the left brake.
Pull the hose off of the left front brake bleed valve, using a shop towel. Wipe away any spilled fluid, then push the rubber dust cap onto the valve.
Refill the master cylinder reservoir with DOT 3 brake fluid until the fluid level is at the halfway point in the reservoir's sight gauge. Reinstall the reservoir lid and inner diaphragm.
Mount the front wheels onto the wheel hubs, then screw the lug nuts into place by hand. Lower the wheels to the ground and remove the jack. Tighten the lug nuts to 47 foot-pounds using a torque wrench.
- Check the reservoir's fluid level often and refill it before the reservoir empties. An empty reservoir will draw air into the brake circuit, forcing you to restart the bleed procedure to remove the trapped air bubbles.
- Always start the bleed procedure with the brake farthest away from the master cylinder.
- Leave the master cylinder reservoir half-full to allow the brake fluid to expand as its heats up though normal use. Over-filling the reservoir can cause the fluid to leak or build up enough pressure to lock the brakes.
- Brake fluid is a solvent and can easily damage painted surfaces as well as causing skin or eye irritation. Cover any painted body panels with a fabric drop cloth and wear protective gloves while working on your TRX 300's brake system.
- Used brake fluid must be taken to a Honda repair facility or an auto parts supply house for disposal.