Copyright Goodheart-Willcox Co., Inc. Heavy Equipment Power Trains and Systems 574 Note The gearing systems found in final drives were detailed earlier in this textbook. • Chapter 6, Belt and Chain Drives—chain drives • Chapter 7, Manual Transmissions—gearing • Chapter 9, Planetary Gear Set Theory—planetary gear sets • Chapter 16, Differentials—spiral bevel gear sets Number of Gear Reductions Machines can have single-reduction, double-reduction, or triple-reduction final drives. The number of reductions equals the number of different gear pairings that work together to provide the final gear ratio. For example, a double-reduction final drive might have two gear sets that work together to produce a final gear ratio of 20:1. The torque entering the final drive is multiplied by 20 and the speed is divided (reduced) by a factor of 20. Refer to Chapter 7, Manual Transmissions, for an in-depth explanation of gear ratios. Final drives may be used in conjunction with a spiral bevel ring and pinion gear set in the differential. For example, a mining truck has a spiral bevel ring and pinion gear set in the differential that provides a torque multiplication and turns the power flow at a 90° angle. The mining truck also has either a single-reduction or double-reduction final drive at the drive wheels. An excavator, on the other hand, uses a hydraulic motor to drive either a double-reduction or triple-reduction final drive. The excavator does not use a spiral bevel ring and pinion gear set. Location of the Final Drives A final drive can be a stand-alone component or integrated into the axle housing. Final drives that are integrated in the axle housing are either inboard or outboard. Inboard final drives are located right next to the differential. Outboard final drives are located near the drive wheels or drive sprockets. Tandem chain final drives are located near the drive wheels on skid steers and motor graders. Final Drives Integrated into the Axle Housing The most common location for integrated final drives is within the drive axle housing (dif- ferential housing). Inboard final drives have a planetary design or a bull-and-pinion gear design. Inboard Single-Reduction Planetary Final Drive An inboard single-reduction planetary final drive attaches directly to the axle’s differ- ential housing. At each side, one of the differential’s side gears drives the planetary sun gear. The ring gear is bolted stationary to the axle housing, and the planetary carrier is the output member and attaches directly to the axle’s driveshaft. See Figure 17-1. The station- ary outer axle housing is sometimes referred to as the trumpet housing because of its shape, Figure 17-2. Machines with inboard planetary final drives include agricultural tractors, wheel loaders, and loader backhoes. Inboard Double-Reduction Planetary Final Drives John Deere manufactures a 9R series four-wheel-drive agricultural tractor with inboard double-reduction planetary final drives. Only the higher-horsepower agricultural