chap98 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 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 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: 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 Figure 98–34 (b) A long handled adjuster tool is needed to turn the side bearing adjuster on this truck 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 SETTING SIDE BEARING PRELOAD After the correct backlash has been determined, the side bearing  must be correctly preloaded To accomplish the proper preload, thicker shims than were used to set proper backlash are placed between the housing and the  differential to provide for the proper preload on the side bearings Always follow the procedures specified for the axle being  serviced A typical axle may require the installation of a shim 0.004 thicker  on both sides. After setting the preload, double­check that the  backlash is within specification. See Figure 98–35 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 98–35 On many axles, it is necessary to use a special tool to install steel spacers (shims) to achieve the specified backlash and side bearing preload 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 What Do I Do About Drive Pinion Bearing Preload When I Replace Just the Pinion Seal? - Part To replace a pinion seal, the drive pinion nut and flange must be removed Before the nut is removed, make a mark on the pinion nut and on the axle housing After the new pinion seal is installed, tighten the pinion nut to the same position it was in before disassembly and then rotate the nut 1/16 inch (1.5 mm) further This extra rotation makes sure that the collapsible space (crush sleeve) is still able to maintain the proper preload on the pinion bearing CAUTION: Do not use an air impact wrench on the drive pinion nut.  The pinion bearings can be damaged by the impact of the wrench 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 What Do I Do About Drive Pinion Bearing Preload When I Replace Just the Pinion Seal? - Part Another method is to measure the rotating torque of the drive pinion using an inch-pound beam-type torque wrench after removing both rear wheels and brake drums After installing the replacement pinion shaft seal, tighten the drive pinion nut until the rotating torque is to in-lb more than the reading obtained before the pinion nut was removed 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 What Is a Spool Rear End? A spool is a solid piece of metal that takes the place of the side gears and pinion gears in a differential assembly A spool used in drag racing is not suitable for street driving because the spool does not allow for any differences in the speeds of the drive wheel during cornering Obviously, drag vehicles not turn corners while racing and the spool rear end is one of the reasons they bounce when turning around at the end of the strip to return to the pits Figure 98–36 A spool used in a rear end for drag racing only 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 REASSEMBLY OF THE DIFFERENTIAL ASSEMBLY After backlash has been checked to be within factory specifications,  the axle shafts can be installed. Install the retaining “C” clip or bolt the  retainer to the axle housing.  Clean and install the  differential cover and fill with the specified  differential lubrication Figure 98–37 Install the axle shaft, being careful to not damage the seal 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 DIFFERENTIAL LUBRICANT Because all differentials use hypoid gear sets, a special lubricant  is necessary because the gears both roll and slide between their  meshed teeth. Gear lubes (GL) are specified by the American  Petroleum Institute (API):  GL­1 Straight mineral oil GL­2 Worm gear lubricant GL­3 Mild EP lubricant (will not protect hypoid gears) GL­4 Mild EP lubricant suitable for manual transmissions/  transaxles GL­5 EP lubricant OK for hypoid gears  (military Mil­L2150B) 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 NOTE: EP additives contain sulfurized esters and organic sulfur  phosphorous compounds. These ingredients give the lubricant a very  strong ­pungent smell. To avoid possible skin irritation, always wear  protective gloves or wash your hands thoroughly with soap and water if  exposed to differential lubricant Most differentials require: SAE 80W­90 GL­5 SAE 75W­90 GL­5 SAE 80W GL­5 Figure 98–38 A container of GL-5 SAE 80W-90 gear lubricant 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 NOTE: Always check the exact specification before adding or replacing  rear axle lubricant Limited­slip differentials (often abbreviated LSD) usually use an  additive that modifies the friction characteristics of the rear axle  lubricant to prevent chattering while cornering HINT: If chattering becomes noticeable while cornering, replace the old  differential lubricant with the correct lubricant and add limited­slip  additives if specified by the vehicle manufacturer. After refilling the  differential, drive the vehicle in a figure­eight pattern at least four times to  help all of the lubricant and additives get into the clutch plates. This  usually stops the chattering­while­cornering problem 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 I Didn’t Know It Would Fit the Wrong Way! An automotive student changed the differential lubricant by removing the housing cover The cover was reinstalled and filled with correct lubricant When the student drove the vehicle it made a grinding sound that was not there before the differential service When the cover was removed, it was discovered that the cover had been installed with the raised area on the right side of the housing instead of on the left side and the ring gear had rubbed a groove in the cover Installing the cover correctly stopped the grinding sound See Figure 98–39 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 I Didn’t Know It Would Fit the Wrong Way! Figure 98–39 The beginning automotive student did not realize that the axle housing cover could fit the wrong way The only problem was that the ring gear scraped against the cover 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 A differential allows the drive wheels to rotate at different  speeds while traveling around a corner or over bumps and dips  in the road The drive pinion transfers torque to the ring gear, which is  attached to the differential case. The case revolves with the  ring gear. The case is equipped with pinion gears that mesh  with side gears. The side gears are splined to the axles When one wheel is rotating faster than the other, the pinion  gears “walk around” the side gears The gear ratio of a differential is determined by dividing the  number of teeth of the drive pinion into the number of teeth 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 SUMMARY (cont.) Most axle assemblies have numbers and/or letters stamped into  the axle housing as an identification A tooth contact pattern test is important to determine if the  relationship between the drive pinion and ring gear is correct The depth of the drive pinion in the differential housing is  critical to the proper operation of the differential A shim pack or a collapsible spacer is used to provide the  proper drive pinion shaft bearing preload Backlash should be about 0.005 to 0.008 inch for most  differentials 10 Many limited­slip differentials use clutches to limit the amount  of slip­page that can occur between the two drive axles 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 ... gear ratio between the drive pinion gear and the driven ring gear The ratio? ?of? ?the final drive (differential) is called the axle ratio.  To determine the axle ratio, divide the number? ?of? ?teeth? ?of? ?the ring  gear (driven gear) by the number? ?of? ?teeth? ?of? ?the drive pinion gear ... lock smoothly without jerking. The pack, lying between? ?at? ?least one? ?of? ?the backs? ?of? ?the side gears and  the case, consists? ?of? ?two types? ?of? ?alternatively stacked steel discs with holes through their middle  sections The first is coated with friction material and the second is not. The interior splines? ?of? ?the friction disc ... gear (driven gear) by the number? ?of? ?teeth? ?of? ?the drive pinion gear  (driving gear): The higher the axle ratio number, the faster the engine rotates for  each rotation? ?of? ?the drive wheels.  Continued Automotive Technology: Principles, Diagnosis, and Service,