  Braking indices of pulsars present a scientific challenge as their
theoretical calculation is still an open problem. In this paper we report
results of a study regarding such calculation which adapts the canonical model
(which admits that pulsars are rotating magnetic dipoles) basically by
introducing a compensating component in the energy conservation equation of the
system. This component would correspond to an effective force that varies with
the first power of the tangential velocity of the pulsar's crust. We test the
proposed model using data available and predict braking indices values for
different stars. We comment on the high braking index recently measured of the
pulsar J1640-4631.
