100 POWER AND THE PLOW 



sun gear is in rotation forward, the internal gear is driven back- 

 ward through these pinions. For the forward motion the 

 entire system moves as a unit. In this system a single lever 

 controls the entire mechanism for forward and reverse travel. 

 The pinion which drives the traction gears fits loosely on the 

 long hub of the reversing disk, and is attached to the belt 

 pulley by a key. This key moves radially on the back of the 

 pulley and enters a slot in a flange cast on the "sun" gear. This 

 pin is operated by a small lever extending through to the outer 

 face of the pulley, so that the pulley can be disengaged from 

 the spur flange pinion at the will of the operator and used for 

 belt driving. 



DIFFERENTIAL 



The differential may be mounted on either the counter- 

 shaft or the real axle. In the former case, which is the rule 

 on the most powerful tractors, power is applied to either wheel 

 by means of a master gear, which is braced to the rim. The 

 spokes then serve only to support the weight of the tractor. 

 The axle often remains stationary, or "dead," both wheels 

 turning upon it. In gas tractors the axle is usually continuous, 

 though short, or stub, axles are occasionally employed. When the 

 differential is located on the real axle, power is applied through 

 the axle, hub, and spokes, which adds a twisting strain to the 

 load upon the latter. The wheels are necessarily independent, 

 hence a sleeve revolving upon the axle is used to drive the 

 wheel which is loose on the axle. In many cases the dif- 

 ferential may be locked, so that if one wheel gets into soft 

 ground the other may propel the tractor out of the difficulty. 



BRAKE 



Control of the tractor on sharp inclines and in other emer- 

 gencies requires the installation of a powerful, quick-acting 

 brake. Where a band- wheel clutch is used in the transmission, 

 a simple form of brake is a shoe on the face of the band- wheel. 



