An experiment is carried out to measure creep groan of a drum brake located in a trailer axle of a truck. The noise nearby the drum brake and accelerations on brake shoes, axle and trailer frame are collected to analyze the occurring conditions and characteristics of the creep groan. A multi-body dynamics model with 1/4 trailer chassis structures is established for analyzing brake component vibrations that generates the creep groan. In the model, the contact force between brake cam and brake shoes, the contact friction characteristics between brake linings and inner circular surface of brake drum, and the properties of chassis structure are included. Dynamic responses of brake shoes, axle and trailer frame during the braking process are estimated using the established model and the responses are compared with the measured results, which validate the model. Three conclusions of measurement and calculation are obtained. (1) The creep groan is usually generated when braking speed is lower than 5km/h and brake pressure changes smoothly. The change of brake pressure causes multiple harmonic vibrations of brake shoes, axle and trailer frame exhibited. (2) The creep groan is generated by stick-slip vibration of contact pair of the brake linings versus the inner circular surface of brake drum, and the vibration is transmitted to the axle through the path of fasteners, welded supports and elastic elements. (3) In this study, the 1st frequency of the collected noise and accelerations are approximately 212 Hz. The 2nd natural frequency of the axle is also close to 212 Hz, indicating that the creep groan is related to structures of chassis system.