Copyright Goodheart-Willcox Co., Inc. Heavy Equipment Power Trains and Systems 822 Note On late-model steering clutch and brake tractors, the proportion the levers are moved determines the proportion of fluid pressure applied to or released from the steering clutches and brakes. For example, when the steering lever is gradually pulled rearward, the steering clutch pressure drops slightly and causes the steering clutch to slip. Steering Clutch and Brake Operation When a steering clutch and brake tractor is moving forward or in reverse in a straight path, both steering clutches will be engaged and both steering brakes will be released. The steering clutch and brake designs vary by manufacturer but typically have the following features: • The steering clutches are normally a multiple-disc design. The steering clutch can be spring applied and hydraulically released, or hydraulically applied and spring released. • The steering brake can consist of a large band and rotating drum or can be a multiple-disc design. • The multiple-disc brake can be spring applied and hydraulically released, or can be hydraulically applied and spring released. • The steering brake can also be used for both the parking brake and the service brake. In Figure 24-14, the steering clutch is hydraulically applied and the brake is spring applied and hydraulically released. The inner axle shaft drives the steering clutch’s input hub. When fluid pressure is applied to the steering clutch pressure cavity, the steering clutch engages, which causes the steering clutch drum to deliver power to the steering brake (output hub). When fluid pressure is applied to the steering brake pressure cavity, the brake releases, which allows the brake’s output hub to drive the outer axle shaft. In order for the tractor to move, oil pressure must be supplied to both the steering clutch to engage it and the steering brake to release it. Oil pressure measurements to the A B 1 2 3 Left steer Right steer Neutral Forward 1st Gear—Left Gradual Steer Forward 2nd Gear—Right Sharp Steer 1 2 3 Left steer Right steer Neutral 1 2 3 Left steer Right steer Neutral Forward 3rd Gear—Forward (Straight Path) 1 2 3 Left steer Right steer Neutral Reverse 1st Gear—Reverse (Straight Path) Transmission gear and speed control lever Left track steering lever Right track steering lever Figure 24-13. An example of an older Caterpillar doser with a mechanical transmission and steering control levers. Note the position of the transmission lever inside the C-shaped slot and the position of the two steering levels. A—The mechanical levers used to control the transmission and the steering clutches and brakes. B—A diagram of the transmission and steering controls. Goodheart-Willcox Publisher Goodheart-Willcox Publisher Reverse Forward Reverse Forward Reverse Forward Reverse Forward