2006 Sequoia Limited, 4 wheel discs, factory rear air ride. Brake pedal just got soft one day and I found the rears weren't working. With the rear tires off the ground the brakes will hold at idle, nothing more. Rear pads were replace about a year before this started. So far I have replaced FL caliper (found one piston frozen), front pads, flushed brake fluid. Today I found that with the rear brake line port on the master cylinder plugged the pedal was still soft/mushy so I put on a new master cylinder. Still no rear brakes. What the hell am I missing?