THE TRACTION GEARING 



127 



Locking the Differential. When both traction wheels 

 have resistance, they pull equally, but if the engine be 

 "jacked up" until one of them is off the ground and free to 

 turn, then when the engine is started, the differential gear 

 will allow the free traction wheel to revolve at twice its 



'OIL GROOVE 

 COUNTERSHAFT ! ; 



FIG. 40. THE DIFFERENTIAL GEAR, SHOWING SPRINGS. 



usual speed, while the traction wheel on the ground will 

 scarcely pull at all. Revolving at twice its usual speed 

 means that the free traction wheel makes, for example, 

 one revolution to nine of the fly-wheel, instead of, to the 

 usual eighteen. Often, when one wheel is in a slippery 

 place, it will spin around, while the other on solid ground 

 remains still without pulling at all. To provide for such 



