Schlage has several options shown below.
The letters GD, HD, BD, or BDC should be put after the lock function. EXAMPLE: ND53BD GD = Schlage SFIC core HD = Construction core BD = Less core BDC = Plastic temporary construction core
The keycam may have failed, example here, the latest design keycam can be easily identified as the colored changed to black. Replace either the keycam or chassis as needed...
 This could also happen if the tailpiece isn't installed in a KIL, FSIC, or SFIC cylinder.  The FSIC driver also could have come loose from the core in the spindle.
The lever removal tool can be used to remove levers in both the ND and the L Series mortise locks.
On August 15, 2012 Schlage began shipping a new, more ergonomic, lever removal tool to coincide with Phase 1 of the ND-Series improvement project.  This tool can be used for Schlage ND-Series ...
The Schlage ND is shipped with a driver/tailpiece when ordered with a LD, BD, or JD suffix.
Only the chassis components are modified for thicker door applications, the lever and spindle assemblies remain intact.  The following parts may be modified depending on the function of the lock ...
Only the Schlage ND-Series can be prepped to accept non-Schlage cores. All designs are supplied with the appropriate tailpiece Non-Schlage cores are NOT included Lever designs available vary d...
The default backset is 2 3/4" and the latch faceplate dimensions are 1 1/8" x 2 1/4". The latch supplied is the 13-047 deadlatch and 13-048 springlatch.