Copyright Goodheart-Willcox Co., Inc. 587 Chapter 17 ∣ Final Drives sun gear to be the input to the last gear set. The third planetary gear set uses a stationary planetary carrier that is attached to the housing, which is bolted to the track frame. The stationary planetary carrier causes the ring gear to propel slowly in a direction opposite of the hydraulic motor shaft rotation. Therefore, to move forward, the hydraulic motor is driven counterclockwise. To move backward, the hydraulic motor is driven clockwise. Excavators can also use two planetary gear sets in the final drive, Figure 17-23. The final drive operates similarly to the final drive in Figure 17-22, but it does not contain the third-stage planetary gear set. The last planetary carrier is also held stationary, causing the ring gear to propel slowly in a direction opposite of the hydraulic motor shaft rota- tion. Examples of excavators that use double planetary gear sets in the final drives are Caterpillar 312E and 319D. Compact Rubber Track Loader Final Drives In many compact rubber track loaders, a hydraulic motor drives the planetary final drive, which propels the drive sprocket. See Figure 17-24. The hydraulic motor commonly is either an inline axial piston motor or a cam lobe motor. The final drive assembly can also have an integrated parking brake mechanism. Case New Holland rubber track loaders have a single-reduction planetary final drive. See Figure 17-25. The hydraulic cam lobe motor spins the shaft with an integrated park brake, which drives the planetary sun gear. The planetary carrier is held stationary, and the ring gear is the output member, which is propelled in a slow reduction in the opposite direction of the hydraulic motor. Track drive sprocket First stage ring gear Second stage ring gear First stage planetary carrier First stage sun gear Second stage sun gear Second stage planetary carrier Hydraulic motor Motor housing mounted to track frame Goodheart-Willcox Publisher Figure 17-23. This simplified excavator final drive uses two planetary gear sets. The hydraulic motor drives the first sun gear. The first planetary carrier drives the second sun gear. The second planetary carrier is held, which causes the ring gear to reverse the direction of rotation.