How to Bleed and Replace Brake Fluid on a 2004 Yamaha Grizzly 660 4X4

Shop parts for a 2004 Yamaha Grizzly 660 4X4 ATV.

This MotoSport-exclusive guide walks you through safely flushing old brake fluid and bleeding the brake systems on a 2004 Yamaha Grizzly 660 4X4. Follow these steps carefully to restore firm brake lever/pedal feel and help prevent corrosion or system failure.

What you’ll need

  • DOT 4 brake fluid (Yamaha recommends DOT 4; do not mix with DOT 5 silicone)
  • Clear plastic hose that fits over bleed nipples
  • Catch bottle for old fluid
  • Brake bleed pump or hand-held vacuum/pressure bleeder OR a helper
  • Open-end wrenches (commonly 8 mm or 10 mm for bleed nipples and banjo bolts)
  • Turkey baster or syringe to remove old fluid from reservoir
  • Clean rags, gloves, and brake cleaner
  • Torque wrench (to reinstall fittings to factory torque)

Key model notes for the 2004 Grizzly 660

  • The Grizzly 660 uses hydraulic front and rear brakes with DOT 4 fluid. Never use DOT 5.
  • There are separate master cylinders for front and rear systems (handlebar lever for front, foot master cylinder for rear). Bleed each master as an independent circuit.
  • Plastic components, painted surfaces, and rubber parts are vulnerable to brake fluid — clean spills immediately with water and brake cleaner to avoid damage.
  • Inspect caliper seals, hoses, banjo fittings, and the reservoir diaphragm while you work; replace any swollen/cracked components to prevent future leaks.
  • Always follow the order furthest-from-master to closest-to-master when bleeding lines to avoid trapping air.

Preparation

  1. Park on a level surface, secure the machine, and remove the keys.
  2. Clean the area around the front and rear brake fluid reservoirs to keep contaminants out.
  3. Remove the reservoir cap and diaphragm carefully; cover the opening to limit debris ingress.
  4. Use a turkey baster or syringe to remove as much old fluid from each reservoir as possible. Dispose of old fluid properly.
  5. Refill the reservoir with fresh DOT 4 fluid to the specified level. Keep the cap and diaphragm nearby but off to the side so you can monitor fluid level during bleeding.

Bleeding procedure – recommended methods

Choose one: manual (helper), vacuum pump, or pressure bleeder. The vacuum or pressure method reduces contamination risk and is easier if you’re working alone.

General bleed order

For each master cylinder (front and rear), identify all calipers/bleed nipples served by that master. Always start with the caliper furthest from the master cylinder and work toward the closest caliper. If you are unsure which caliper is furthest, trace the brake line routing visually.

Using a vacuum bleeder

  1. Slip clear tubing over the caliper bleed nipple and place the other end in a container partially filled with old fluid.
  2. Attach the vacuum pump to the bleed nipple. Open the nipple about a 1/4 turn with the appropriate wrench.
  3. Apply vacuum and gently operate the brake lever (front) or press the brake pedal (rear) several times, then hold it down as fluid and air evacuate. Continue until clear, bubble-free fluid appears.
  4. Close the bleed nipple, release vacuum, then tighten nipple to snug (final torque to factory spec when possible).
  5. Top off the reservoir and repeat for the next caliper in order. Keep the reservoir level above the minimum at all times.

Using a pressure bleeder

  1. Fill the pressure bleeder reservoir with DOT 4 and attach it to the brake fluid reservoir per the bleeder instructions.
  2. Pressurize per tool directions and open the furthest bleed nipple. Let fluid flow until clear and bubble-free, then close the nipple.
  3. Repeat for each caliper moving toward the master, topping the reservoir as needed.

Manual bleed with a helper

  1. Attach clear tubing to the bleed nipple and submerge the other end in a jar with old fluid.
  2. Have your helper slowly apply and hold the brake lever or pedal while you open the bleed nipple. Fluid and air will push into the jar.
  3. Close the nipple before the helper releases the lever to prevent drawing air back in. Repeat until the fluid is clear and free of bubbles.
  4. Work through calipers from furthest to closest and keep the reservoir level topped up.

Tightening & final checks

  • When each bleed nipple is closed, torque banjo bolts and bleed nipple fittings to factory specs if available; if unsure, tighten securely and inspect for leaks during a short test ride.
  • Replace reservoir diaphragm and cap. Clean any spilled fluid from painted surfaces immediately.
  • Test lever and pedal feel at low speed in a safe area. Brakes should feel firm and consistent. If sponginess persists, repeat bleeding until all air is removed.
  • Check for leaks around calipers, hoses, master cylinders, and banjo fittings after the test ride and re-torque if necessary.

Maintenance tips specific to the Grizzly 660

  • Change brake fluid every 1–2 years or sooner if it becomes dark or contaminated; moisture absorbs into DOT fluid and reduces boiling point.
  • Inspect hose routing at the swingarm and steering linkages for chafing during regular service intervals; replace any hose with visible cracking or swelling.
  • Keep the reservoir cap and diaphragm in good condition to avoid contamination in the closed system.
  • If you ride in muddy or wet conditions often, inspect and clean caliper pistons and seals more frequently.

Troubleshooting

  • If brake feel never firms up: check for flexible hose swelling or internal master cylinder leak — replace suspect components.
  • If you get fluid leaking at a union after bleeding: tighten, clean, and recheck; replace copper crush washers on banjo fittings if needed.
  • If corrosion or pitting is found on rotor surfaces, service or replace rotors to ensure effective braking.

Performing a proper fluid replacement and bleed will restore braking performance and extend the life of the Grizzly 660’s hydraulic components. If you encounter persistent issues, consult a qualified technician or authorized service for a deeper inspection.

Related Shopping Categories

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Shop Brake Lines for a 2004 Yamaha Grizzly 660 4X4 ATV.

Shop Brake Tools for a 2004 Yamaha Grizzly 660 4X4 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.