We report intrinsic tunneling data for mesa structures fabricated on three over-and optimally-doped Bi 2.15 Sr 1.85 CaCu 2 O 8+δ crystals with transition temperatures of 86-78 K and 0.16-0.19 holes per CuO 2 unit, for a wide range of temperature (T) and applied magnetic field (H), primarily focusing on one overdoped crystal (OD80). The differential conductance above the gap edge shows a clear dip structure which is highly suggestive of strong coupling to a narrow boson mode. Data below the gap edge suggest that tunnelling is weaker near the nodes of the d-wave gap and give clear evidence for strong T-dependent pair breaking. These findings could help theorists make a detailed Eliashberg analysis and thereby contribute towards understanding the pairing mechanism. We show that for our OD80 crystal the gap above T c , although large, is reasonably consistent with the theory of superconducting fluctuations.