  We use the framework of a relativistic constituent quark model to study the
semileptonic transitions of the Bc meson into CCbar charmonium states where
CCbar = etaC (1S0), J/psi (3S1), chiC0 (3P0), chiC1 (3P1), hc (1P1), chiC2
(3P2), psi (3D2). We compute the q^2-dependence of all relevant form factors
and give predictions for their semileptonic Bc decay modes including also their
tau-modes. We derive a formula for the polar angle distribution of the charged
lepton in the (l nu) c.m. frame and compute the partial helicity rates that
multiply the angular factors in the decay distribution. For the discovery
channel [B_c => J/psi (=> mu+ mu-) l nu] we compute the transverse/longitudinal
composition of the J/psi which can be determined by an angular analysis of the
decay J/psi => mu+ mu-. We compare our results with the results of other
calculations.
