Copyright Goodheart-Willcox Co., Inc. Heavy Equipment Power Trains and Systems 576 In a John Deere 8000 series MFWD tractor front steer axle, the axle shaft provides input to the outboard planetary gear set’s sun gear. The ring gear is held stationary to the axle’s housing. The planetary carrier is the output member and is coupled to the wheel’s drive hub, which drives the wheel. See Figure 17-5. Many rigid-frame quarry trucks use outboard single-reduction planetary final drives in the drive axle (rear axle). A rigid-frame quarry truck final drive normally propels dual tires. See Figure 17-6. Large wheel loaders can have outboard single-reduction planetary final drives in both the front and rear drive axles. These axles are non- steer axles because the loader has articulation steering. See Figure 17-7. Articulated dump trucks and mining wheel loaders can also be equipped with outboard single-reduction final drives. See Figure 17-8. Outboard Double-Reduction Planetary Final Drives Mining wheel loaders, mining trucks, and articulated agricultural trac- tors can be equipped with outboard double-reduction planetary final drives that are incorporated into the axle housing. The two planetary gear sets are connected together in series. See Figure 17-9. Caterpillar Outboard Double-Reduction Planetary In a Caterpillar outboard double-reduction planetary final drive, the differential’s side gear delivers power to the first reduction sun gear. Both ring gears are coupled to the spindle and are held stationary. The first reduction planetary carrier delivers power to the second reduction gear set’s sun gear. The second reduction planetary carrier propels the drive wheels. Axle housing First stage stationary ring gear Second stage stationary ring gear Service brake disc Final drive’s pinion gear Pinion shaft driven by the differential’s side gear Final drive’s bull gear Driveshaft Drive hub Ring gear (stationary) Planetary carrier Sun gear Goodheart-Willcox Publisher Figure 17-3. High-horsepower John Deere 9R series four-wheel-drive agricultural tractors and scraper tractors have inboard double-reduction planetary final drives. This front axle assembly is on display at the US National Farm Progress show, providing a clear view to the underside of the front axle assembly. The bar axles are missing from the axle assembly. Goodheart-Willcox Publisher Figure 17-4. This bull-and-pinion final drive was removed from a compact utility tractor after the gears’ teeth failed. The splines on the left side of the pinion shaft mate with the differential’s side gear. The splines on the right side mesh with the service brake disc. Goodheart-Willcox Publisher Figure 17-5. A cutaway of the front axle in an 8000 series John Deere tractor. The planetary carrier is coupled to the drive wheel’s hub. The right side driveshaft is driven by the MFWD differential’s side gear and splined to the planetary gear set’s sun gear. The sun gear is the input member to the outboard planetary final drive. The axle housing holds the ring gear stationary, and the planetary carrier is the output member and is coupled to the drive hub.