2000 Yamaha YFM400FWA(M) Factory Service workshop Manual, Page 275Get this manual
FRONT AND REAR BRAKES
3.Inspect: Brake fluid level Refer to "BRAKE FLUID LEVEL INSPECTION" in CHAPTER 34.Check: Brake lever or brake pedal operation Soft or spongy feeling Bleed the rear brake systemRefer to "AIR BLEEDING (HYDRAULIC BRAKE SYSTEM)" in CHAPTER 3