Mimicking neutron star precession by polar cap current-pattern drifting
  We propose a model for rotating current patterns within radiopulsar polar cap accelerators which has observational consequences that mimic those which have been attributed to neutron star free precession. The model is a simple extension of a canonical one for the origin of the "drifting subpulses" often observed within the pulse envelope of radiopulsars.   The new model's current pattern rotation period (with respect to the neutron star) is estimated to be of order a year. Associated with that rotation are small oscillations in spin-down torque, pulse arrival time, and radiobeam direction with this same period. These have estimated magnitudes which support a reinterpretation of free precession "observations" which could resolve the severe problem of obtaining anywhere near the otherwise required precession parameters with canonical neutron star models. 
M. Ruderman and J. Gil