Mechanically controllable break junctions of the heavy-fermion superconductor have been investigated. Josephson-like I - V characteristics could be found only for low-ohmic contacts, but without the oscillatory pattern of the critical current in a magnetic field. High-ohmic contacts always had a finite residual resistance as if there was a normal layer at the contact. Some of these contacts showed Andreev-reflection-like features in the differential resistance , while resistive transport usually affected them. We have also realized true vacuum tunnelling: the exponential dependence of the current on the width of the vacuum gap and the transition from tunnelling to metallic contact indicate a nearly free-electron mass of the tunnelling charge carriers, as well as a typical metallic carrier density of . The temperature dependence of the tunnelling current yields direct information about the thermal-expansion coefficient of the samples and its anisotropy. The superconducting features of the I - V characteristic vanish when the contact resistance exceeds about . They could not be resolved by vacuum tunnelling, pointing to a pair-breaking effect of the heavy-fermion interfaces.