126 SCIENCE OF SUCCESSFUL THRESHING 



nion-ring. The clutch sleeve is most liable to wear in 

 plowing or hauling where the clutch is frequently used. 

 In this class of work, the sleeve of the clutch-arm must 

 be kept well lubricated. 



The Differential Gear. In order to have both traction 

 wheels pull, when the engine is traveling either forward or 

 backward, and at the same time allow one wheel to travel 

 further than the other in turning corners, the differential 

 gear is necessary. It transmits the power from the inter- 

 mediate gear to the two counter-shaft pinions, which mesh 

 with the spur gears on the traction wheels. The four 

 bevel pinions are carried by the center casting, and mesh 

 with two bevel gears, one of which is cast in one piece with 

 the right-hand counter-shaft pinion (which is loose upon 

 the shaft), and the other of which is keyed to the counter- 

 shaft and drives the left-hand counter-shaft pinion (which 

 is also keyed to the shaft). It will be seen that when the 

 engine travels straight ahead, both counter-shaft pinions 

 turn with the shaft and the whole differential revolves as 

 one piece. In turning corners, however, the bevel pinions 

 revolve, permitting one of the counter-shaft pinions to re- 

 volve faster than the other, thus allowing the traction 

 wheels to accommodate themselves to the curve of the road. 

 The differential spur wheel is a separate piece from the 

 center casting, the power being transmitted from the rim 

 to the center casting through coil springs, which relieve 

 the gearing of the shocks of starting and stopping the en- 

 gine. 



