Copyright Goodheart-Willcox Co., Inc. Heavy Equipment Power Trains and Systems 836 • No gear shifting (similar to a hydrostatic drive). • The electric drive system has 60% fewer moving parts as compared to the powershift transmission. • The electric drive powertrain components are expected to last up to 50% longer than traditional drive components (in similar conditions) and are configured in easy to replace modules. • A tractor designed with no engine accessory drive belts, which improves machine serviceability. Chapter 26, Electric and Hybrid Drive Systems, will describe the D7E in greater detail. Note Caterpillar is unique in that they manufacture a tractor model line with each of the four different types of track steering systems: • Hydrostatic drive tractors (small dozers, D3K2–D6K2, and loaders, 953K, 963K, and 973D). • Steering clutch and brake tractors (large dozers, D10T2 and D11T). • Differential steering tractors (midrange dozers, D6T–D9T). • An electric drive track-type tractor (D7E). Tractors Equipped with Four Track Undercarriages In 1996, Case IH introduced a rubber track tractor with four individual track undercar- riages, called the Quadtrac®, Figure 24-30. The tractor is similar to other large four-wheel- drive agricultural tractors that use hydraulic articulated steering, which is explained in Chapter 25, Wheeled Steering Systems. Examples of other manufacturers who produce an articulated rubber track tractor are John Deere, New Hol- land, and Versatile. John Deere manufactures a 764 HSD high-speed dozer with four rubber tracks and an agricul- tural 9RX four track tractor, Figure 24-31. Articulated track-type tractors operate in a similar fashion to the traditional four-wheel-drive agricultural tractor. The tractors use traditional hydraulic articulated steering, have full-time four track drive, are equipped with lockable differentials, and do not use any type of twin track steering, such as differential steering, dual-path hydrostatic drive, or steering clutches and brakes. Goodheart-Willcox Publisher Figure 24-30. One of the original Case IH Quadtrac tractors. Philip McNew Figure 24-31. The John Deere 9620RX rubber track tractor and the Case IH Quadtrac. Note A few machines are equipped with a rigid frame and four rubber track undercarriages, and do not use traditional twin track steer- ing systems or articulation steering. Some agricultural row crop tractors can have their four wheels replaced with four rubber tracks. These tractors use a front steerable axle like traditional row crop tractors. Ditch Witch® manufactures a rigid frame four track trencher that uses front and rear steerable axles, known as four-wheel steer. Chapter 25, Wheeled Steering Systems, explains four- wheel steer in more detail.