How to Bleed and Replace Brake Fluid on a 1990 Yamaha YFM350ER MOTO-4
Shop parts for a 1990 Yamaha YFM350ER MOTO-4 ATV.
This MotoSport-exclusive guide walks you through a safe, effective brake fluid change and bleed procedure tailored for the 1990 Yamaha YFM350ER MOTO-4. It covers tools, a step-by-step method, troubleshooting, and model-specific notes owners should know about maintenance and aging components.
Before you begin – safety & preparation
- Work on a flat, stable surface with the engine off and key removed.
- Wear safety glasses and nitrile gloves. Brake fluid is corrosive to paint & plastics.
- Use only fresh, sealed brake fluid of the type specified by the bike – DOT 3 or DOT 4 are commonly used on this era of Yamaha; verify the cap marking before purchasing.
- Protect painted surfaces with rags and use a catch container for expelled fluid. Dispose of old fluid per local hazardous-waste rules.
- Have replacement parts on hand if needed: bleed hose, crush washers for banjo fittings, replacement rubber hoses and caliper seals if lines or seals are cracked or brittle.
Tools & supplies
- Fresh DOT 3 or DOT 4 brake fluid (confirm reservoir cap marking)
- Clear vinyl tubing that fits snugly over bleed nipples
- Small catch bottle and a hand-held vacuum pump or syringe (preferred for cleaner bleeding)
- Open-end wrenches for bleed nipple (usually 8mm or 10mm)
- Line clamp or zip-ties, rags, funnel, gloves, safety glasses
- Optional: new crush washers for banjo bolts and replacement hoses if original lines are aged
Model-specific notes for the 1990 Yamaha YFM350ER MOTO-4
- This ATV is now an older machine; rubber brake hoses and caliper seals commonly harden or crack. Inspect lines for swelling, cracks, or soft spots before bleeding. Replace suspect lines prior to introducing fresh fluid.
- Brake fluid contamination is common in long-stored machines. Expect dark, discolored fluid and plan to flush until fluid runs clear.
- Bleed nipple locations are on the calipers and master cylinder assemblies. The front system uses handlebar master cylinder(s); the rear uses a foot-operated master cylinder near the engine frame. Lift or remove any small covers to access reservoirs on this model.
- Banjo bolt fittings at calipers may be brittle with age; have a backup plan for seized fittings — penetrating oil and correct-size tools, and be cautious to avoid rounding bolts.
Step-by-step: replacing brake fluid & bleeding the system
- Locate reservoirs. Clean the caps and surrounding area thoroughly to prevent dirt entering the system when opened.
- Remove reservoir cap & diaphragm. Siphon or absorb as much old fluid from the reservoir as possible to reduce contamination when topping up.
- Top the reservoir with fresh fluid to the recommended level. Keep the reservoir topped during the entire bleeding process to avoid drawing air in.
- Start with the caliper furthest from its master cylinder (if front/rear separate, bleed the rear master cylinder system first if it's the furthest). For each caliper: place clear tubing over the bleed nipple and route into the catch bottle partially filled with a little brake fluid to avoid air re-entry.
- Using a vacuum pump or syringe at the bleed nipple, apply steady suction while an assistant gently squeezes and releases the brake lever or pedal. If using the lever/pedal method without a pump, have the assistant hold pressure when the nipple is closed to avoid sucking air back in.
- Open the bleed nipple about 1/4 turn while pumping; fluid and air bubbles will travel into the tubing. Close the nipple before the lever/pedal is released. Repeat until no air bubbles appear and fluid runs clear.
- Top off the reservoir frequently between cycles to prevent drawing air into the master cylinder.
- Repeat the process for every caliper/master cylinder in the correct sequence: furthest to nearest relative to its master cylinder. For split front/rear systems, bleed the rear master and caliper assembly(s) first, then front.
- With all bleed nipples closed, pump the brake lever/pedal to build firm pressure. If the lever/pedal feels spongy, repeat bleeding until firm.
- Torque bleed nipple and banjo fittings to proper snugness without over-tightening. Wipe any spilled fluid, replace reservoir diaphragm & cap, and check brake light switch operation if applicable.
- Road-test the ATV at low speed in a safe area to confirm braking performance. Recheck reservoir level and inspect for leaks after the first short ride.
Troubleshooting & tips
- Persistent sponginess: inspect master cylinder internal seals and caliper pistons for damage. Old seals often need replacement on a 1990 model.
- Seized caliper pistons: use caliper rebuild kits and replace dust boots. Do not force a corroded piston without proper tools.
- Mixing fluids: never mix synthetic DOT 5 (silicone) with DOT 3/4. Stick to DOT 3 or DOT 4 as indicated on your reservoir cap.
- If banjo bolts or fittings are rounded or seized, replace them rather than risk stripping threads; MotoSport carries OEM-style replacements to restore reliability.
Final inspection & maintenance schedule
- After bleeding, inspect all lines, fittings, and calipers for leaks periodically over the next 24-48 hours.
- For older ATVs like the 1990 YFM350ER, plan to replace rubber hoses and caliper seals every few years or at first sign of wear to maintain braking integrity.
- Brake fluid should be changed every 1-2 years or sooner If the fluid darkens; regular replacement prevents moisture accumulation and internal corrosion.
Following this procedure will restore a firm brake pedal/lever feel and refresh the hydraulic system on your 1990 Yamaha YFM350ER MOTO-4. For model-specific replacement parts and kits, visit the MotoSport parts page provided above to find compatible hoses, seals, and caliper rebuild kits tailored to your ride.
Related Shopping Categories
Shop Brake Fluid for a 1990 Yamaha YFM350ER MOTO-4 ATV.
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Shop Brake Lines for a 1990 Yamaha YFM350ER MOTO-4 ATV.
Shop Brake Tools for a 1990 Yamaha YFM350ER MOTO-4 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.