A master thesis within mechanical engineering performed by two student has been conducted at Scania in Oskarshamn. The purpose has been to investigate if Discrete Event Simulation using ExtendSim can be applied to increase Scanias assembly productivity. The projectiles was to investigate how the buffer systems could be managed by vary the amount of buffers and their transport speed. The assembly line takt times with regard of their availability was also investigated. The method of approach was to build a simulation model to gaining valid decision making information regarding these aspects. Process stop data was extracted and imported to ExtendSim where the reliability library was used to generate shutdowns. Comparing 24 sets over 100 runs to each other a median standard deviation of 0,91 % was achieved. Comparing the total amount of assembled cabs over a time period of five weeks with the real timedata a difference of 4,77 % was achieved. A difference of 1,85 % in total amount of shutdown time was also achieved for the same conditions. The biggest effect of varying buffer spaces was for system 6A. An increasement of up to 20 more assembled cabs over a time period of five weeks could then be achieved. By increasing all the buffertransports speeds by 40 % up to 20 more assembled cabs over a time period of ve weeks could be achieved. A push and pull system was also investigated where the push generated the best results. A 22 hour decreasement of total shutdown time and an increasement of 113 more assembled cabs over a time period of ve weeks could be achieved.