The clutch coupling teeth are designed to slide axially in order to accommodate some machine axial expansion. What actually happens as the machinery grows axially, is that the thrust forces at the toothed coupling (and the machinery thrust bearings) build gradually, until that axial force is enough to overcome the coupling internal friction, then the axial movement takes place over a very short time (jumps) and the axial forces are thus reduced to a lower level. This may take place over a few steps as the machine temperature changes.