Ford F-650 2001 Owner's Manual page 112

Driving
Parking brake warning chime — F650 SuperCrewzer Only
If a chime sounds when pulling the yellow knob out, your parking brake
is not functioning properly, seek service immediately. This chime will
sound until the yellow knob is pushed in or eight minutes have passed. If
the yellow knob is pulled out again the chime sounds as a reminder that
immediate service is required to the parking brake system.
Releasing spring brake manually — F650 SuperCrewzer Only
Do not attempt to disassemble the parking brake chamber under
any circumstances. The high spring load may cause serious
injury if the chamber clamps are removed.
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 prevent the vehicle from moving.
Unexpected and possibly sudden vehicle movement may occur if
these precautions are not taken.
Remove the clevis which is attached
to the end of the spring chamber
rod. This can be done by using a
wrench on the flats of the rod to
thread it out of the clevis. There is
sufficient thread length in the clevis
to fully release the parking brake.
112