chap99 pps Automotive technology at University of Cambridge

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 99, the reader should be able to: • Prepare for ASE Manual Drive Train and Axles (A3) certification test content area “F” (Four-Wheel Drive Component Diagnosis and Repair) • • Explain the difference between a mode shift and a range shift Describe the purpose and function of the center 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 OBJECTIVES: After studying Chapter 98, the reader should be able to: • • • Explain the purpose and function of a viscous coupling Describe the difference between four-wheeldrive and all-wheel drive Explain how the front axle is disconnected when two-wheel drive is selected 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: annulus gear bevel gear differential electronically controlled clutch assembly input member • interaxle differential (center differential) • internal gear locking hubs • low range mode shift output member 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 KEY TERMS: part-time four-wheel drive • planet carrier • planet Pinions range shift • reaction member • ring gear sun gear 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 FOUR WHEEL DRIVE SYSTEMS Two-wheel drive vehicles use engine torque to turn either the front or the rear wheels A differential is required to allow the drive wheels to travel different distances and speeds while cornering or driving over bumps or dips in the road A four-wheel-drive vehicle requires two differentials—one for the front wheels and one for the rear wheels NOTE: The term x means a four-wheeled vehicle that has engine torque applied to all four wheels (four-wheel drive) A x is a fourwheeled vehicle that has torque applied to two wheels (two-wheel drive) 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 Four-wheel-drive vehicles require more than just two differentials The front and the rear wheels of a four-wheel-drive vehicle also travel different distances and speeds whenever cornering or running over dips or rises in the road There are three different methods used to allow for front-to-rear driveline speed variation 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 Method 1—Locking Hubs Engine torque from the transmission is applied directly to the rear differential through the transfer case The transfer case permits the driver to select a low-speed, highpower gear ratio inside the transfer case while in four-wheel drive Figure 99–1 Many light trucks and sport utility vehicles use a transfer case to provide engine torque to all four wheels and to allow a gear reduction for maximum power to get through mud or snow (Courtesy of Dana Corporation, Perfect Circle Products) 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 CAUTION: Check the owner’s manual or service manual for the recommended procedure to follow when changing from one position to another in the transfer case Some vehicles require that the vehicle be stopped before selecting between two- and four-wheel drive and between high and low range These positions and their meanings include: 4H four-wheel drive with no gear reduction in the transfer case 4L four-wheel drive with gear reduction Use of this position is usually restricted to low speeds on slippery surfaces 2H two-wheel drive (rear wheels only) in high range, meaning no gear reduction in the transfer case 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 The transfer case also applies power to the front differential Power is then applied to the front wheels through the drive axles to the locking hubs In normal 4H driving on hard surfaces, the front hubs must be in the unlocked position The front hubs are locked when-ever driving on loose road surfaces to absorb and allow for tire slippage due to the different tire speeds front to back This type of four-wheel-drive system is called part-time fourwheel drive because it can only be driven in four-wheel drive on slippery surfaces See Figure 99–2 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 Keep the Differential Vents Clear All differentials are vented to allow for expansion and contraction of differential lubricant in all temperature ranges Typically, these vents are shielded openings near the top of the differential Most trucks, especially four-wheel-drive vehicles, use an extended vent hose to prevent water from getting into the differential if the vehicle is driven in deep water If mud gets into the vent, pressure can build up inside the differential and cause lubricant leakage past the rear axle seals Whenever replacing rear axle seals, always check to make sure that the differential vent is clear Remember that four-wheel-drive vehicles use two differentials and that both the front and rear vents plus the vent on the transfer case should be checked 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 DIAGNOSING AND SERVICING LOCKING HUBS Locking front hubs should be cleaned periodically, especially if the vehicle has been driven under water or in dusty conditions Most vehicle manufacturers recommend that the hubs be cleaned and lightly coated with grease at the same time the front wheel bearings are serviced Check the service information for the exact procedure for the vehicle being serviced See Figure 99–27 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 99–27 (a) An exploded view of a Dualmatic ® manual locking hub (b) A Warn® manual locking hub (a) (b) 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 Start the inspection of the front hubs by removing the cover plate Many problems associated with locking hubs can be corrected by cleaning and lubricating the components If noise is heard from the hubs, carefully inspect the inner components on both sides of the vehicle A damaged part can cause noise in the hub on the other side Service kits are often available for the hubs and contain gaskets, seals, and retaining rings necessary for installing the hubs correctly after wheel bearing or front brake work has been completed NOTE: Check the amount of axle end play Excessive end play caused by defective bearings can cause the drive axle to move enough to damage the hubs 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 The Differential Lubricant Story - Part A four-wheel-drive vehicle was serviced and both differentials were drained and refilled as recommended by the vehicle manufacturer The owner returned shortly after picking up the vehicle and complained that the vehicle drove as if the parking brake was still applied The vehicle lacked power and would decelerate rapidly whenever the accelerator pedal was released Careful inspection of the parking brake revealed that everything was functioning correctly Because all that was done was the differential fluid service, the fluid level was checked and again, the level was correct and not overfull Then the technician checked the container of gear lubricant that was used and discovered that the parts store had accidentally sent SAE 80W-140 instead of the requested, and more commonly used, SAE 80W-90 Both lubricants were listed GL-5 meaning that they were acceptable for differentials 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 The Differential Lubricant Story - Part The container of lubricant had been installed in the portable lubricating dispenser when it was delivered, and therefore the label on the container was not visible to the technician The correct lubricant was installed in the differential and normal vehicle performance was restored The technician and the parts store learned to double-check the product before shipping or using it 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 TRANSFER CASE SERVICE Transfer cases usually require occasional lubricant change during normal service life Driver abuse often causes parts to break, requiring the overhaul or replacement of the entire assembly Always follow the vehicle manufacturer’s recommended servicing procedure 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 PHOTO SEQUENCE NV-242 Transfer Case Service 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 PHOTO SEQUENCE NV-242 Transfer Case Svc (cont.) 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 PHOTO SEQUENCE NV-242 Transfer Case Svc (cont.) 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 PHOTO SEQUENCE NV-242 Transfer Case Svc Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman (cont.) ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY A x is a four-wheel vehicle that has engine torque applied to all four wheels, whereas a x is a four-wheel vehicle that has engine torque applied to just two wheels Part-time four-wheel drive means that four-wheel drive should only be used on a slippery surface because the transfer case does not include a center differential to allow for differences in front-to-rear wheel rotational speeds Most part-time four-wheel-drive vehicles use either manualor\ automatic-locking front hubs All four-wheel-drive vehicles should be towed with all four wheels off the ground if possible to avoid possible drivetrain damage 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 SUMMARY (cont.) Full-time four-wheel-drive vehicles use a center differential All-wheel-drive vehicles usually not have a low range transfer case and are therefore not suited for serious off-road usage The center differential can be locked to provide additional traction by the use of either a viscous coupling or an electronically controlled clutch assembly A mode shift selects two-wheel drive or four-wheel drive, whereas a range shift selects either low range, neutral, or high range 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 SUMMARY (cont.) Some four-wheel-drive vehicles use Cardan-type U-joints for the front wheels, which may cause driveline vibration during rapid acceleration while cornering 10 Transfer cases may use either automatic transmission fluid (ATF) or SAE 80W-90 gear lube 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 end 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 ... (Courtesy of Dana Corporation, Perfect Circle Products) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc... DIFFERENTIAL AXLE RATIOS In most four-wheel-drive vehicles, the overall gear ratio of the front differential is slightly higher than the overall ratio of the rear differential The overall ratio is determined... RATIO CHART See the chart on Page 1277 of your textbook Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc