Ford 2007 F-650 Owner's Manual page 104

yellow control knob is pulled out again, the light will blink and the chime
will sound as a reminder that immediate service is required to the
parking brake system.
Releasing spring manually
Do not attempt to disassemble the parking brake chamber under
any circumstances. The high spring load may cause serious
injury.
If air pressure is released from the spring brake chamber the power
spring applies the brake and, unless air pressure can be re-established,
the spring brake must be released as follows in order to move the
vehicle.
Block the wheels to help prevent the vehicle from moving.
Unexpected and possibly sudden vehicle movement may occur if
these precautions are not taken.
Loosen the jam nut (1) and un-thread the adjustment rod (2) from the
chamber to reduce tension on the cable (3). Continue to un-thread the
adjustment rod all the way and remove it from the chamber. The nut and
shaft are metric.
2007 F-650/750 (f67)
Supplement
USA (fus)
Driving
103