  Gear box dynamics is characterised by a periodically changing stiffness. In
real gear systems, a backlash also exists that can lead to a loss in contact
between the teeth. Due to this loss of contact the gear has piecewise linear
stiffness characteristics, and the gears can vibrate regularly and chaotically.
In this paper we examine the effect of tooth shape imperfections and defects.
Using standard methods for nonlinear systems we examine the dynamics of gear
systems with various faults in meshing stiffness.
