the equipment is moving forward or backward. Thisdesign lessens rolling resistance in soft ground, becauseone set of tires prepares a path for the other set.Additionally, this design provides maximum control ofthe direction of the load. Also, it enables the equipmentto be held on a straight course and permits short turns inproportion to the maximum angle of the wheels.In crab steering, both sets of wheels are turned inthe same direction. If both sets of wheels are turned atthe same angle, the machine moves in a straight line atan angle to its centerline. Results can be obtained fromeither four-wheel steering or crab steering by usingdifferent turning angles on independently controlledfront-and-rear wheels.SUSPENSION SYSTEMSA suspension system anchors and suspends thewheels or tracks from the frame with springs, as shownin figure 3-5. It supports the weight and allows thevehicle to be driven under varying loads and speedconditions over bumpy roads and rough terrain withoutgreat risk of damage.miles. The spring assemblies of the suspension systemshould be checked regularly to ensure that shackles aretight and that bushings within the shackles are notoverworn or frozen tight. Occasionally, sprayinglubricating oil on the spring leaves helps to preventsqueaking at the ends of the spring leaves. Following thelubrication chart for a particular vehicle, check andlubricate the front suspension system, includinglinkages, kingpins, and ball joints. During your checksyou may find shock absorber bushings worn. If so,document it and turn it in so the problem can be lookedat. The Construction Mechanic (CM) inspector maydecide the shock absorbers should be replaced.Some symptoms of suspension troubles in vehicleoperation that should be documented and turned in forrepair are as follows:. Hard steeringl Vehicle wandersl Vehicle pulls to one side during normal drivingl Front-wheel shimmyAlthough suspension systems are a part of yourl Front-wheel tramps (high-speed shimmy)prestart and operator maintenance responsibilities, theyusually do not need to be adjusted or replaced for manyl Steering kickbackFigure 3-5.—Front axle suspension system.3-4
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