2000 Ford F-550 Super Duty XLT 8 Cyl 7.3L
Is there a check valve in the system?
Front brakes are working fine, but the back brakes wont apply and there is no air in them but plenty of fluid.
Nissan Technical Advisor 1/26/2011
Could be the combination valve where the secondary piston controls the rear brakes assembly is stuck or worn or the piston calipers or the slave pistons at the rear are worn out. You have to check those possible troubles and removal of the unit is required for inspection.