Copyright Goodheart-Willcox Co., Inc. 583 Chapter 17 ∣ Final Drives with factory-equipped tracks use a bull- and-pinion final drive with a different ratio because the track frame carries the structural load. John Deere 9000 series and 9010 series combines also use a final drive that has a planetary gear set. A bull-and-pinion produces the first reduction and a plane- tary gear set produces the second reduc- tion. See Figure 17-17. Tandem Chain Drives In some off-highway machines, tandem chain drives propel tandem drive wheels. A tandem chain drive consists of a pair of drive sprockets that drive a pair of chains and driven sprockets that are splined to a drive wheel. Each side of the machine has two chains used to propel a set of tandem wheels. Examples include skid steers and motor graders. Skid steer chain drives have a hydro- static motor on each side of the machine that provide the input to the chain drive. In many skid steers, a single-speed or two-speed hydraulic motor directly drives the two small drive sprockets. See Figure 17-18. The skid steer’s drive sprockets have their own separate chain and propel a large wheel sprocket (driven sprocket). A driven sprocket is splined to each drive wheel's axle. See Figure 17-19. In motor grader tandem chain drives, a traditional power shift trans- mission sends power to a differential. Figure 17-16. This Case IH combine final drive uses a bull-and-pinion gear set for the first reduction and a planetary gear set for the second reduction. A—The pinion gear has been set beside the bull gear to show how the pinion drives the bull gear. B—On the back side of the bull gear is the 33-toothed planetary sun gear, which meshes with the three planetary pinion gears. A B Input pinion gear (16 teeth) Planetary carrier pinion gear Output drive hub Bull (reducer) gear (73 teeth) Planetary ring gear (75 teeth) Planetary carrier Sun gear (33 teeth) Bull (reducer) gear (73 teeth) Drive hub splined to planetary carrier Planetary carrier Pinion gear (16 teeth) Goodheart-Willcox Publisher Figure 17-17. This John Deere 9600 combine uses a combination bull-and-pinion and planetary gear set final drive. Right drive axle Three-speed transmission Hydrostatic drive motor Left drum brake Final drive planetary gear set Final drive bull-and-pinion gear set Left drive axle Goodheart-Willcox Publisher Goodheart-Willcox Publisher