In this research, ride quality of a truck is investigated to understand vibration specifications of the multi-degree of freedom 3-axle rigid truck. for this purpose, a Benz 2624 model have been modelled. An off-road duty is considered for this analysis. A modeling procedure and simulation of the truck is produced in this research. The system is modelled by a linear model which contains the seat and cab suspensions, rigid live axles, and also suspension geometries, the motion equations and system matrices are obtained by utilizing the Lagrange?s equation. Then, a numerical central difference method is utilized to gain the system responses subject to the sinusoidal road excitations. Truck?s physical parameters and dynamic properties of its components are not well-known therefore these properties have been achieved by modeling the truck in SOLIDWORKS software. Finally, a code based on these equations is developed in MATLAB software to calculate system time responses under different cases, which contains low and high drive frequency of the truck. The developed model can also be used for newer trucks with some modifications to change the current model it?s necessary to have accurate information for input data.