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This paper deals with the synchromesh behaviour of the manual car gearbox. Firstly, the state of the art on Borg-Warner-type synchronizers is presented. Then, the gear-changing process is studied and eight main operating phases are defined. The phases are described using classical tribological, mechanics, and thermodynamics theories. Models are interconnected to describe synchronizer behaviour and they are included in a numerical simulation software. Measured data are compared with the results of simulation software. Then, stick-slip phenomenon during gear changing is studied. Stick-slip is supposed to be present in two contact zones: sleeve splines and the synchronizer cone. The effects in both zones are discussed. Finally, the double bump phenomenon is studied. Double bump is assumed to be the maximum axial operating force coming from short successive phases at the end of the gear-changing process. Due to the angular integer division of splines and to the non-definite angular position of mechanical parts, sliding sleeve displacement into the ring and gear claw clutch splines gives secondary angular rotation and large increases in the axial operating force. The model can explain large variations and random dispersion of the measured double bump force peaks.