Copyright Goodheart-Willcox Co., Inc. Heavy Equipment Power Trains and Systems 820 As mentioned, a hydrostatic-propelled track-type tractor has a much simpler system design and can eliminate items 2 through 9. In Chapter 9, Planetary Gear Set Theory, the power flow through a Caterpillar three- speed dozer transmission is explained. Once the operator selects the transmission speed and direction, the power exits the transmission and is delivered to two helical transfer gears, which deliver power to a bevel gear set. See Figure 24-8. The bevel ring gear drives the hollow shaft to which the inner axle shafts are internally splined. Both inner axle shafts transfer power to the accompanying left and right steering clutches and brakes. Based on how the operator moves the dozer’s drive controls, power moves through and then exits the steering clutches and brakes via the outer axle shafts. The outer axle shafts deliver the power to the right and left final drives, which function as the mechanisms driving the track undercarriages on both sides. Pro Tip There are instances when a technician must remove the axle shafts so the tractor can be towed. For example, if the engine or transmission is inopera- tive and the machine needs to be moved into the shop, such a procedure would be necessary. On a Caterpillar steering clutch and brake dozer with an elevated sprocket, the axles are removed through the center of the final drives, Figure 24-9. A slide hammer can be used to remove the axle shafts. Be sure to follow the manufacturer’s service procedures. Warning The tractor’s parking brake is no longer effective once the axle shafts are removed. If the dozer is positioned on a slope, the tractor will roll down the slope if the axle shafts are removed. Steering Clutch and Brake Controls Steering clutch and brake tractors commonly have mechanical levers or electronic fingertip switch con- trols for propulsion and steering. See Figure 24-10. Goodheart-Willcox Publisher Figure 24-8. The transfer gear and bevel gear sets are incorporated into the transmission housing. After the transmission speed and direction are selected by the operator, power is sent to the transfer gear set, which sends power to the bevel gear set. The bevel ring gear drives the shaft that mates with the two inner axles. Only one of the two transfer gears is visible in the photo. Goodheart-Willcox Publisher Figure 24-9. A Caterpillar steering clutch and brake tractor with an elevated sprocket has two inner axle shafts and two outer axle shafts that are both removed through the center of the final drives. A—Inner axle shaft. B—Outer axle shaft. Back of Transmission Front of Transmission Power input Helical transfer gear Inner axle shaft cavity Bevel ring gear A B