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Before we get into it, lets start with the basics of the car differential; whether it be gas, diesel, hybrid, or electric. A cars power source delivers a certain amount of power to the wheels via a driveshaft, or a front differential transaxle in the case of a frontwheeldrive car. The power produced by this driveshaft needs to be split to drive the two wheels. Thats why differentials exist: to split the power between the wheels while allowing them to travel at different speeds. There isnt just one gear in a car differential or diff, but a few different parts.
start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 98, the reader should be able to: • • • Prepare for ASE Manual Drive Train and Axles (A3) certification test content area “E (Rear Axle Diagnosis and Repair) Describe how the differential allows engine torque to be applied to both drive wheels and still allow a difference in the speed of the drive wheels during cornering Determine the rear axle ratio Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 98, the reader should be able to: • • • • Perform a tooth contact pattern check and determine corrective action Describe how to determine proper drive pinion gear depth Explain how to achieve proper drive pinion bearing preload Describe how to adjust the ring gear position to provide the proper backlash Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: axle ratio coast (or concave) side • companion flange • crown diff • differential case • drive (or convex) side • drive pinion gear floating position heel • hunting gear sets • hypoid gear set lap nonhunting gear sets Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Continued ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: partially nonhunting gear sets • pinion gear • pinion shaft • preloaded clutch rear end • ring gear • ring gear runout • root side gears • spider gears • straddle-mounted pinion toe • turning torque • viscous coupling Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PURPOSE AND FUNCTION OF A DIFFERENTIAL The differential allows engine torque to be applied to both drive axles, which rotate at varying speeds during cornering and while traveling over bumps and dips in the road The differential also changes the direction of engine torque 90° from the rotation of the driveshaft lengthwise with the vehicle These two purposes of a differential can be summarized as follows: To change the direction of engine torque See Figure 98–1 To allow the drive wheels to rotate at different speeds See Figure 98–2 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 98–1 The differential assembly changes the direction of engine torque and increases the torque to the drive wheels Figure 98–2 The difference between the travel distance of the drive wheels is controlled by the differential Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 A differential is a mechanical addition and subtraction assembly By splitting the engine torque to the drive wheels when the vehicle is turning a corner, the torque forces cause the side gear and pinion mate gears to subtract torque from one side and add torque to the opposite side Figure 98–3 When the vehicle turns a corner, the inner wheel slows and the outer wheel increases in speed to compensate This difference in rotational speed causes the pinion gears to “walk” around the slower side gear Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PARTS OF A DIFFERENTIAL A differential is also called a rear end or abbreviated simply as a diff Whenever any vehicle makes a turn, the outside wheel must travel a greater distance than the inside wheel The driveshaft applies torque to the drive pinion gear that meshes below the center line of a ring gear as shown here Figure 98–4 A hypoid gear set uses a drive pinion that meshes with the ring gear below the center line of the ring gear Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 This type of gear set is called a hypoid gear set and requires gear lubrication specifically designed for this type of service The ring gear is attached to a differential case that also contains small beveled spider gears or pinion gears A pinion shaft passes through the two pinion gears in the case In mesh with the pinion gears are two side gears that are splined to the inner ends of the axles See Figure 98–5 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458