This study investigates the significance levels of the clutch pedal effort parameters in heavy duty vehicles with manual transmission. A non-linear multibody dynamic model of the clutch system is developed to show the effect of clutch system parameters on clutch pedal performance in an experimental design. The most critical factors are selected the release load on release bearing, mechanical ratio, clutch servo assist air pressure, hydraulic ratio, expansion loss ratio, spring forces. The two level factorial designs for each critical factor represent the experimental design. The results of the study show that clutch servo assist air pressure has the most significant effect on the pedal effort, and the level selected in the experimental design is an important parameter for the reliable results.