Ford 2003 Mustang Workshop Manual page 2634

Transmission will not shift
into one gear—all others
OK
Transmission is locked in
one gear and cannot be
shifted out of that gear
Transmission leaks
Crankshaft pilot
bearing.
Internal
damage.
Gear teeth.
Manual shift
linkage.
Backup switch
ball.
Internal
components.
Internal
components.
Fork on rail.
Lubricant.
INSTALL a new bearing.
INSPECT the
synchronizer sleeves for
free movement on their
hubs. INSPECT the
synchronizer blocking
rings for widened index
slots, rounded clutch
teeth and smooth
internal surface. CHECK
countershaft cluster gear
for excessive end play.
CHECK shift forks for
worn or loose mounting
on shift rails. INSPECT
the synchronizer sliding
sleeve and the gear
clutch teeth for wear or
damage. REPAIR or
INSTALL a new
component as
necessary.
If worn or damaged,
INSTALL new gears.
REFER to Section 308-
03A or Section 308-
03B .
REPAIR or INSTALL
new components as
necessary.
If REVERSE is the
problem, CHECK
backup switch for ball
frozen in extended
position.
INSPECT the shift rail
and fork system,
synchronizer system and
the gear clutch teeth for
restricted travel.
REPAIR or INSTALL
new components as
necessary.
INSPECT the problem
gears, shift rails, forks
and the synchronizer for
wear or damage.
REPAIR as necessary.
REFER to Section 308-
03A or Section 308-
03B .
CHECK the shift rail
interlock system.
REFER to Section 308-
03A or Section 308-
03B .
CHECK the level and
type.