Copyright Goodheart-Willcox Co., Inc. Heavy Equipment Power Trains and Systems 824 Caution The steering brakes can be used for both a parking brake and service brakes. As described in Chapter 12, Hydrodynamic Drives, a dozer torque converter should not be stall tested in a low transmission gear because the tractor often has enough torque to drive through the parking brake. Steering Clutch and Brake Disadvantages Steering clutch and brake tractors must slow or completely stop one track in order to steer. They are not capable of counter rotating. Hydrostatic-propelled tractors, differential- steered tractors, and electric drive tractors have power applied to both tracks during a turn, which allows the tractor to maintain a constant speed while making a turn. Examples of Steering Clutch and Brake Track-Type Tractors Some manufacturers still use steering clutch and brakes for controlling track steering on their highest horsepower tractors. Caterpillar’s two largest dozers, the D10T2 and D11T, have steering clutches and brakes. Komatsu’s two largest dozers, the D375A-6 and D475A-5, also have steering clutches and brakes equipped. Dressta® dozers (formerly International dozers) have a steering clutch and brake system installed in their TD-8R, TD-9R, and TD-10R dozers. Differential Steering Systems Multiple manufacturers offer a twin track steering system that is often referred to as differential steering. A differential steering system does not contain a traditional differ- ential. It instead uses planetary gear sets, bevel gears, spur or helical gears, and a reversible hydraulic motor to provide variable power to twin track tractors. The tractor’s opera- tor can infinitely vary the speed between the right and left tracks. As the operator steers the tractor, the steering differential increases the speed of one track and proportionately reduces the speed of the other track. Tractors equipped with differential steering are capa- ble of counter rotation. See Figure 24-16 for examples of tractors with differential steer- ing systems. Although differential steering system designs and nomenclature vary, some similarities do exist between the different systems. Differential Steering Operation In a differential steering system, the steering differential receives either one or both of the following inputs. The first is a hydraulic steering motor input, which determines the direc- tion of the turn (left or right) and how sharp of a turn is made. The second is a powershift transmission input, which determines the speed and the direction of the tractor’s propul- sion (forward or reverse). The steering differential delivers uninterrupted power to the tracks through two output shafts, a right and left axle shaft, which drive a right and left planetary final drive respectively. Manufacturer Tractor Steering Nomenclature AGCO MT Challenger twin rubber track tractors Differential steering Caterpillar D6T, D8T, and D9T dozers Differential steering Case New Holland (CNH) Case 1650K and 1850K dozers Fiat Kobelco D180 New Holland DC150 and DC180 Power steer John Deere 8000T–8000RT and 9000T–9000RT rubber twin track tractors Differential steering Komatsu D65EX-17, D85EX-15, D155AX-7, and D275AX-5 dozers Hydrostatic steering system (HSS) Goodheart-Willcox Publisher Figure 24-16. Examples of differential-steered twin track tractors.