THE TRACTION GEARING. 



IOI 



the other on solid ground remains still without pulling at 

 all. To provide for such emergencies, the hub of the left 

 traction wheel is made so that a pin can be inserted and both 

 wheels locked to the axle. This, of course, makes both trac- 

 tion wheels revolve together, and prevents the differential 

 i 



gear from working. The engine must be steered straight 

 when the lock-pin is used, or broken gearing is liable to 

 result. 



FIG. 34. THE DIFFERENTIAL GEAR, SHOWING SPRINGS 



Oiling the Differential. The journals of the bevel-pin- 

 ions in the differential and the hub of the left traction wheel 

 should be oiled occasionally. The left-hand or inside bevel- 



