I took out my dirt bike out after a long summer break. As I started going down the hill I noticed I had no rear break. The break is there but pressing on the plunger causes no pressure on pads. Inspected the fluid level and it's fine. Lines are free of obstructions and undamaged. I am no mechanic but I can usually find my way around my bike but this one has me puzzled. Any ideas why the pressure is gone?