Copyright Goodheart-Willcox Co., Inc. 829 Chapter 24 ∣ Track Steering Systems Hydraulic Steering Motor At the heart of a differential steering system is a reversible hydraulic motor that provides an input into the steering differential any time the operator directs the tractor to steer. Many differential-steered tractors use a stand-alone hydraulic pump and hydraulic motor that are dedicated solely for providing a hydraulic input to the steering differential. If the hydraulic schematics for a differential steering system and a traditional closed- loop hydrostatic transmission (HST) are compared, the two will look identical. However, the hydraulic steering pump and motor in the differential are not used for propulsion, but are used only when the tractor is being steered. The HST closed-loop reverse and forward drive lines mirror the steer left and steer right pressure lines in the differential steering system. The first Caterpillar differential-steered dozer, the D8N, did not use a closed-loop hydraulic steering pump and motor. The system obtained steering oil from the implement pump and used a directional-control valve for controlling the direction of oil flow to the reversible hydraulic motor. Case New Holland differential-steered tractors also do not use a stand-alone closed-loop steering pump and motor, but use oil flow from the implement pump. Differences between Hydrostatic Transmission and Differential Steer Hydrostatic-propelled dozers share similarities with differential-steered tractors. They both feature variable track control to deliver uninterrupted power to each track. Both sys- tems can also counter rotate at various speeds. The hydrostatic-propelled tractor uses dual-path controls, which means the right and left track are controlled independently by their own hydrostatic pump and motor. The Ring gear Sun gear Hydraulic steering motor Bevel ring gear Bevel pinion gear Transfer shaft Planetary carrier Steering brake Sun gear Bevel gear shaft Input from transmission Motor pinion gear Gear A Gear C Gear E Gear B Gear D Goodheart-Willcox Publisher Figure 24-22. The Komatsu hydrostatic steering system is a differential steering system similar to the system equipped in a John Deere twin rubber track tractor. Note that on this illustration of the D275AX-5 dozer’s system, the dashed line between Gears A and B indicates the two gears are in mesh.