Front Brake Master Cylinder Rebuild Kit Compatible with 2001-2005 Yamaha Bolt Raptor 660 4BA-W0042-50-00 ATV Sport Gaitor boot Yamaha YFZ Brake fluid contamination 5TG-W0042-50-00 New

Front Brake Master Cylinder Rebuild Kit — Yamaha Raptor 250/660 / YFZ 450

Kit Contents:
• Master cylinder piston — OEM specification
• Return spring — factory tension spec
• Primary seal — high-temperature DOT 4 compatible
• Secondary seal — prevents fluid bypass
• Gaitor boot (dust cover) — keeps contaminants out
• Circlip — secures piston assembly
• Copper crush washers — for banjo bolt sealing
• Red rubber assembly grease — protects seals during installation

Applications:
• Yamaha Raptor 250 (2008-2013) including SE
• Yamaha Raptor 660 (2001-2005) including LE and SE
• Yamaha YFZ 450 (2004-2009) including Bill Ballance, LE, and SE editions

Function:
The front brake master cylinder converts lever pressure into hydraulic pressure to actuate the brake caliper. Over time, internal seals wear and degrade, causing brake fade, spongy lever feel, fluid leaks, or complete loss of front braking. This rebuild kit replaces all wear components to restore full braking performance.

When to Rebuild:
• Brake lever pulls to handlebar even after bleeding
• Visible fluid leak at master cylinder body or lever pivot
• Spongy or inconsistent brake feel
• Brake fluid discoloration (dark or cloudy fluid)
• During routine maintenance every 2-3 years or as needed

Installation Notes:
• Clean master cylinder bore thoroughly before installing new components
• Apply included red rubber grease to seals during assembly
• Use fresh DOT 4 brake fluid — never reuse old fluid
• Bleed brake system completely after rebuild
• Verify no air in system — lever should feel firm with no sponginess

ADDITIONAL CROSS-REFERENCES:
• One kit fits all listed Yamaha sport ATV models
• Replace when brakes feel spongy, lever pulls to bar, or fluid leaks