The coupled torsional and transverse vibration of a back-to-back gearbox system has been investigated experimentally and analytically. Receptance methods were used to model the system, and were shown to be effective. A detailed experimental modal analysis was performed using the swept-sine technique with an a.c. servomotor torsional exciter. Torsional excitation allowed for the dynamic response to be measured up to 1600 Hz. The model included a combination of lumped mass elements and continuous shafts with distributed inertia and damping. The bearings were modelled as having both radial and tilt stiffness and damping elements. The model simulated the experimental results well and predicted each of the first 11 natural frequencies to within 8 per cent. Of the 11 natural frequencies, 9 simulated deflected shapes matched very well, validating the modelling approach taken for the project together with the assumptions made in the derivation of the model. This paper presents the detailed results of a full torsional/transverse model analysis of the gearbox system.