downhill and also as an emergency brake to effectively reduce the vehicle 39 s speed a mechanical finger commanded by the lever fetters output shaft 22 option 1 we will call 34 link zone 34 the time interval initiated when the centrifuqal force produced by counterweights 12 begins to overcome the resistance spring 92 and finished with the full engagement of coupling 3 11 the force developed by spring 92 must be such that the link zone is within the limits of velocity for which the box needs to change from 2nd to 3rd speed or vice versa if in experimenting with this gear box in a car it is found that such link zone is excessively long coupling 3 11 can be replaced by the system crank 23 spring 14 illustrated in fig4 this system has no link zone but its dynamic equilibrium is more difficult than that of the former system also in this case the energy taken by spring 14 from the motor to extend is returned to the vehicle 39 s wheels when the spring shrinks disk 4 is now a part of a rolling bearing which tends to counteract the deflection stresses produced by spring 14 disk 33 is fixed to crank 23 arms 38 may be rigidly supported by disk 4 or ca be articulated to respond to the centrifugal force developed by means of weights 12 so profiting from the fact that disk 4 is fixed to the output shaft 22 so that the angular speed of the disk will be proportional to that of the vehicle 39 s wheels spring 14 will introduce another elastic element to the box thus improving its performance in 3rd speed in this case.