Heavy commercial duty vehicles have been used to for many years. High energy dissipation is required to stop these types of vehicles. Selection of brake type is related with the brake resists to this physical and environment conditions and also comfortability of drivers and passengers. Brake squeal is the most common costumer complaint for brake systems. This problem is main interest and tackled in many ways. In this thesis, vibration characteristics of the heavy commercial duty brake system, which is a drum brake, is studied by Finite Element Method to analyze the brake squeal. Natural frequencies and mode shapes of drum and shoe which are in frictional contact are determined by using ANSYS. Block Lanczos solver is preferred for this analysis. Experimental modal tests are accomplished to compare finite element results with experimental ones. Then, the noise characteristics of the brake system are obtained by performing a series dynamometer tests. In these experiments, four parameters are selected to investigate the decreasing and eliminating the noise. The selected parameters are deceleration rate, pressure, temperature and friction coefficients. The results are presented in tables and graphs.